Fisheries and Aquaculture by Abdul Hameed Korai ( Tehsildar )

Fisheries
and
Aquaculture
Compiled by: Hameed Korai

All praise to Almighty Allah who enabled me to present this
piece of work in a precise and illustrative manner. This book has
been compiled according to the syllabus of Fisheries prescribed
by Universities Grants Commission and University of
Balochistan, Quetta, Thus it covers the syllabi of all the
universities of Pakistan. This book has been furnished by all the
required material and diagrams in a simple but elaborative
manner.I hope this manual will prove useful to both teachers
and students equally.
My heartiest gratitude is for my teachers, whom I owe the
concept of subject. I would like to thanks all of my colleagues,
friends and well wishers who inspired and practically helped me
to complete this prestigious work. I am specially thankful to my
friend Tahir Habib, Shahnawaz Silachi, Taimoor Shakeel,
Shoaib Ahmed, Altaf Hussain, Aftab hussain, Saddam Hussain,
Wajid Hussain, Akhtar Hussain, Zahid Ali and Abdul Qadeer
who encouraged to do this work.
Fisheries
and
Aquaculture

Fisheries notes by Abdul Hameed Baloch Ph. 0306-3707078
3
Some Culturable fishes of Pakistan with their
scientific and common name

4

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LECTURE NO. 1
INTRODUCTION TO ICHTHYOLOGY
Outline:
� Diversity of Fishes
� Definition of fish
� Habitat
� Distribution
� Origin of fishes
� Size extremes
� Shapes
DIVERSITY OF FISHES:
� Vertebrates make just 5%
of the total living species of
Animal kingdom and have 55
thousand species.
� Out of these 55 thousand species more than half the number of species are of
fishes.
� Fishes have an estimated 30 thousand species and make a wonderful world of
animals.
� Numerically, valid scientific descriptions exist for approximately 27,977 living
species of fishes in 515 families and 62 orders (Nelson 2006).
� The study of fish is called Ichthyology and the person who studies ichthyology
would be known as ichthylogy.
� Peter Artidi is known as the father of ichthyology.
� fishes are placed in the large group of animals called peices.
� A question may arise in the mind of a zoologist that what is a fish!!!
DEFINITION:
Fish is an aquatic cold blooded chordate having atleast following features:
� 1. Gills for respiration
� 2. Fins for locomotion
� 3. Scales for protection
� 4. Two chambered for blood circulation

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External anatomy of fish
The head
Mouth Shape/ Position
Superior Mouth
Also known as an undershot or upturned mouth
Eats food above the fish
May eat at the water‟s surface
Terminal Mouth
Eats food in front of it
Inferior Mouth
Also known as an underslung mouth
Eats food below it
May eat off of the bottom
Gills
Allows gas exchange for the fish
Through the gills, fish are able to absorb oxygen and give off carbon dioxide
Operculum
The gill cover
Barbels
Also known as whiskers
located under the mouth of a fish
are tactile and taste organs used for locating food in dark or muddy waters
The body
The body covering
covered with scales, which protect the body
Most fish get extra protection from a layer of slime that covers their scales called
mucus.
Scales
Made of calcium, they are outgrowths of the skin

7
They overlap like shingles on a roof so that the skin of the fish is not exposed
The scales of a fish lie in pockets in the dermis and come out of the connective
tissue.
Scales do not stick out of a fish but are covered by the Epithelial layer.
The ridges and the spaces on some types of scales become records of age and
growth rate.
Types of Scales
Cycloid scales
Have a smooth edge on the backside
Found on soft-rayed fish
Ctenoid scales
Have teeth-like projections along the backside
Found on spiny-rayed scales
Placoid scales
Are similar to teeth
Made of dentin covered by enamel
Ganoid scales
Flat and basal looking
They overlap very little
Lateral line
It is a series of fluid-filled ducts located just under the scales
picks up vibrations in the water
fish are able to detect predators, find food, and navigate more efficiently
help the fish detect water pressure changes
It can detect minute electrical currents in the water
It runs in a semi line from the gills to the tail fin. It can be easily seen in fish as a
band of darker looking scales running along the side.
Peduncle
The edge of the tail fin that lies on the end or outside of the caudal fin
Fins
Paired and Unpaired

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Paired fins
Pectoral and the pelvic fins are the paired fins
Pectoral fins
A paired fin
located near the gill cover
used for manoeuvring the fish
Sometimes the pectoral fins are equipped with spines for defence
Related to the front legs or arms
Pelvic or ventral fins
A paired fin
located forward of the anal fin
are used to provide further stability in swimming
times these fins are modified as long, thread-like fins used as a tactile organ
Relate to the hind legs
HABITATS:
� Fishes live in aquatic environment ( called hydrospere part of earth).
� Today, and in the past, fishes have occupied nearly all major aquatic habitats,
� from lakes
� and polar oceans that are ice-covered,
� to tropical swamps, temporary ponds, intertidal pools, ocean depths,
� and all the more benign environments that lie within these various extremes.
(Helfman)
DISTRIBUTION:
� When broken down by major habitats,
� 41% of species live in fresh water,
� 58% in sea water,

9
� and 1% move between fresh water and the sea during their life cycles (Cohen
1970). � Geographically, the highest diversities are found in the tropics.
ORIGIN OF FISHES:
� The exact origin of fishes is still unknown
� however scientists believe that fishes may have originated about 500 million
years ago in the early devonian period.
SIZE:
� fishes have variety of sizes.
�The worlds smallest fishes and vertebrates mature at around 78 mm
� and include an Indonesian minnow, Paedocypris progenetica,
� and two gobioids, Trimmatom nanus from the Indian Ocean
� and Schindleria brevipinguis from Australias Great Barrier Reef (parasitic males

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of a deepsea anglerfish Photocorynus spiniceps mature at 6.2 mm, although
females are 10 times that length).
�The worlds largest fish is Whale shark (rhyncodon typus) which has a
tremendous length of 12.5 meters.
SHAPE.
Diversity in form includes relatively fishlike shapes such as minnows, trouts,
perches, basses, and tunas, but also such unexpected shapes as boxlike trunkfishes,
elongate eels and catfishes, globose lumpsuckers and frogfishes, rectangular ocean
sunfishes, question-mark-shaped seahorses, and flattened and circular flatfishes
and batfishes, ignoring the exceptionally bizarre fishes of the deep sea.

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THE MAIN CULTURABLE FISHES OF
PAKISTAN
Outline:
1. Labeo Rohita
Geographical Distribution
Morphological Characters
2. Catla catla
3. Miragal Carp
4. Hypophthalmichthys
molitrix
5. Ctenopharyngodon idella
6. Oncorhynchus mykiss
7.Aristichthys nobilis
Morphological Character
1. Labeo Rohita
Rohu (Labeo rohita)
This fish is commonly found in Pakistan, India, Nepal, Bangladesh, Burma,
Thailand, China, Kampuchea and Sri Lanka.

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Its body is deep and dorsal profile is more concave than abdomen. Snout is obtuse
and compressed, projecting beyond the jaws. Lips are thick and fringed with
distinct inner fold. Generally one pair of small maxillary barbells is present and
sometimes a second rostral pair is present. Lateral line scale are 40-42. Color of the
body is bluish or brownish along the back and silvery on the sides and beneath.
Usually a red mark is present on each scale.
2.
Thaila (Catla catla)
Pakistan, India, Nepal,
Bangladesh, Burma,
Thailand, China, Kampuchea
and Sri Lanka.
It possesses elongated body,
curved on ventral and dorsal
sides. There is pair of small
barbells on upper jaw. Mouth
is small. Body is scaled
except mouth and head. Red spot on each scale. Dorsal side of body is bluish and
silvery on the side
3. Mrigal (Cirrhinus mrigala)
This fish is commonly found in Pakistan, India, Russia, Nepal, Bangladesh,
Burma, Thailand, China, Kampuchea and Sri Lanka.
A large fish, body oblong and
moderately compressed.
Width of head equal to length
behind the eyes which is
located in the anterior half of
the head. One pair of barbells
present. Scales of moderate
size; lateral line scales 40 to

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45. caudal fin deeply forked. Color of the body is silvery, dark gray along the back,
sometimes coppery. Pectoral, ventral and anal fins are tinged with black. Eyes are
golden
4. Silver carp (Hypophthalmichthys molitrix)
It is native of south, central and northern China and Russia, transplanted in Europe
south Asia, south east Asia and Africa.
This fish has elongate and
moderately compressed body.
Head is short and rounded snout.
Upper jaw is slightly longer than
the lower. Barbells are absent.
Caudal fins is forked and lateral
line is curved. Scales on the body
are of moderate size. The color of
the body is silvery and fins are
slightly blackish.
5. Grass carp (Ctenopharyngodon idella)
It is native of south, central and northern China and Russia, transplanted in Europe
south Asia, south east Asia and Africa.
This fish has elongate and
moderately compressed body,
broad head with short and
rounded snout. Upper jaw is
slightly longer than the lower.
Barbells are absent. There are
two rows of compressed,
comb-like teeth in throat.
Scales on the body are of

14
moderate size. The fish is dark gray above and silvery on the belly.
6. Rainbow Trout
(Oncorhynchus mykiss)
It is famous game fish all over the world. It inhabits cold water and lives higher
altitude all over the world. It is cultured in northern area like Kagan, Chitral, Swat
of N.W.F.P and Quetta of Balochistan and Muree of Punjab. It is regarded as very
good angling fish. It is native of south, central and northern China and Russia,
transplanted in Europe south Asia, south east Asia and Africa.
This head, upper region of the body and dorsal fins of the fish are mottled with red
and black spot. Small black spots are also present under the lateral line of the body.
Ventral surface of the body is dark gray in color. Body is short and stout. Male and
female can be distinguished during the spawning season. In the male the lower jaw
is triangular in shape and is longer than the upper jaw; while this is not the case in
female. Male become much darker in color during the spawning season but the
female looks more bright.
7. Aristichthys nobilis (Big Head)

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LECTURE NO. 2
HISTORY OF ICHTHYOLOGY
ARISTOTLE
Outline
Aristotle
Guillaume Rondelet—De Piscibus Marinum
George Markgraf's
John Ray & Francis Willoughby
Carolus Linnaeus
Peter Artedi
� (384-322 B.C.)
� first scientific description of fish� (118 spp.)
Guillaume Rondelet—De Piscibus Marinum
� (1500 )
� He described (244 spp.)
George Markgraf's
� (1686)
� Naturalis Brasilae (100 spp.)
John Ray & Francis Willoughby
� ( 1686)
� Historia Piscium (<400 spp.).
Carolus Linnaeus
� (1670-1738)
� Carolus (Karl) Linnaeus
�“father of taxonomy”(1670-1738)
� develops binomial nomenclature
� (two name, genus species)
� Genus Species
� Oncorhynchus mykiss

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� Common name: Rainbow trout
Peter Artedi
� (1732)
�“The father of ichthyology"
� a student of Linnaeus
� who identified five orders of aquatic and marine animals
� (including cetaceans) and divided those into genera.
� In 1732 both left Uppsala:
� Artedi for England, and Linnaeus for Lapland;
� before parting they reciprocally bequeathed to each other their manuscripts and
books in the event of death.
� How fortunate for them! In an untimely demise,
Artedi got drunk
� and drowned in Amsterdam canal!
� Linnaeus published his manuscripts
posthumously.
Marcus Elieser Bloch
� (1780)
� Ichthyologia as a series of volumes of plates.
� Johann Gottlob Schneider pub. M. E. Blochii
Systemae
� Ichthyologiae (1,519 spp.)
Georges Cuvier
� (1800)
� Regne animal distribué d’après son
organisation (key step forward for fish
classification).
� Cuvier also worked with his student Achille
Valenciennes
� to produce the 22-volume Histoire Naturelle
des Poissons (never completed)
� yet 4,514 spp.
Albert Günther
�(1800s)

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� Catalogue of the Fishes of the British Museum�<6,800 d (another 1,700
mentioned).
Charles Darwin
� (1859)
� Origin of the Species,
� animals placed within a common genus
� shared ancestral lineage.
David Starr Jordan
� (1900)
� (greatest ichthyologist at the time)
� wrote 650 articles and books on fish.
� He was also president of Indiana and Stanford Universities.
B. W. Evermann
� (1896-1898)� Fishes of North America described
� ALL fish known in N. America and Panama at the time (4 volumes).
Leo Berg (1947)
� Russian paleoichthyologist
� who combined study of fish and fossil records,
� Classification of Fishes,
� Recent and Fossil.
� First introduced the concept of “iformes” to endings of fish orders,
eliminated confusion.
Greenwood et al.
�(1966) � produced the first modern classification of the majority of present day
fishes.
Balon et al.
� (1994) � compilation of contributions to ichthyology by women scientists.
Many resources for fish information.
Texts: Moyle and Cech 1996, Bond 1996, Bone 1994.
Journals: Copeia, Transaction of the American Fisheries Society, North American
Journal of Fisheries Management, Aquaculture, Journal of the World Aquaculture
Society, North American Journal of Aquaculture, Journal of Fish Biology, Journal

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of Ichthyology, etc...
Internet: www.fishbase.org, www.aquanic.org, www.afs.org

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LECTURE NO. 3
CLASSIFICATION OF LIVING FISHES
Subphylum Vertebrata (ver te-bra tah)
“Agnathans” (ag-nath ans)
� Lack jaws and paired appendages;
� cartilaginous skeleton;
� persistent notochord;
� two semicircular canals.
� (Hagfishes have one semicircular canal
that may represent a fusion of two
canals.)
Class Myxini (mik s˘ı-ne)

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� Mouth with four pairs of
tentacles;
� olfactory sacs open to mouth
cavity;
� 5 to 15 pairs of pharyngeal slits.
� Hagfishes.
Class Cephalaspidomorphi (sef-
ah-las pe-do-morf e)
� Sucking mouth with teeth and
rasping tongue;
� seven pairs of pharyngeal
slits;
� blind olfactory sacs.
� Lampreys.
“Gnathostomes” (na tho-
stomes )
� Hinged jaws and paired appendages;
� vertebral column may have replaced notochord;
� three semicircular canals.
Class Chondrichthyes (kon-drik thi-es)
� Tail fin with large upper lobe (heterocercal tail);
� cartilaginous skeleton;
� lack opercula and a swim bladder or lungs.
� Sharks, skates, rays, ratfishes.
Subclass Elasmobranchii (e-laz mo-bran ke-i)
� Cartilaginous skeleton may be partially ossified;
� placoid scales or no scales.
� Sharks, skates, rays.
Subclass Holocephali (hol o-sef a-li)
�Operculum covers pharyngeal slits;
� lack scales;
� teeth modified into crushing plates;
� lateral-line receptors in an open groove.

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� Ratfishes.
Class Osteichthyes (os-te-ik-the-es)
� Most with bony skeleton;
� operculum covers single gill opening;
� pneumatic sacs function as lungs or swim bladders.
� Bony fishes.
Subclass Sarcopterygii (sar-kop-te-rij e-i)
� Paired fins with muscular lobes;
� pneumatic sacs function as lungs.
� Lungfishes and coelacanths (lobe-finned
fishes).
Subclass Actinopterygii (ak tin-op te-rig-e-i)
� Paired fins supported by dermal rays;
� basal portions of paired fins not especially muscular;
� tail fin with approximately equal upper and lower lobes (homocercal tail);
� blind olfactory sacs. Ray finned fishes.
(Zoology by miller and harley)
Chondrichthyes and vs Osteichthyes
Cartilaginous fishes (Chondrichthyes)
Examples:Sharks, rays and Skates
Characteristics of cartilaginous fish

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1. Cartilaginous endoskeleton.
2. Gills are exposed to the outside.
3. Mouth on the ventral side of the head.
4. Swim bladder absent.
5. Placoid scales.
6. Fertilization is internal.
Bony fishes (Osteichthyes) fishes
Examples: Salmon, Flying fish, Sea horse, Rohu, trout
Characteristics of Bony fishes
1. Bony endoskeleton.
2. Gills covered by operculum.
3. Mouth at terminal end of the head.
4. Swim bladder present.
5. Cycloid and ctenoid scales.
6. Fertilization is external.

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HARD ANATOMY

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LECTURE NO. 4 FISH BODY FORMS
External Form
� Provides a quick appraisal of its way of life
� Most fish can be put into
one of several body categories
� There are exceptions for
specialized lifestyles
Fusiform (streamlined)
� Often called rover-predators
� Constantly on the move
� Always searching for prey
� Pointed head
� Terminal mouth
� Narrow caudal peduncle
� Forked tail
� Fins evenly distributed l
� Characteristic of stream fish
Compressiform (laterally
compressed)
� Capable of quick bursts of
speed
� Not in constant motion
� Predatory fish
Depressiform (flattened
dorsoventrally)
� Bottom-dwelling fish
� A few are adapted to swim
in open water
� Large pectoral fins for
movement
� Rays and skates
Anguilliform (eel-shaped)
� Blunt or wedge-shaped

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heads
� Tapering or rounded tails
� Fins are small to absent
� Adapted to moving through crevices
� Many are predators of small invertebrates
Filiform (thread-shaped)
� Extreme version of eel-shape
� Largest part of body is the head
Taeniform (ribbon-shaped)
� Eel-like, but compressed
Sagittiform (arrow-shaped)
� Often lie-in-wait predators
� Most are piscivores
� Use quick burst of speed to emerge from hiding place
� Dorsal fin near caudal peduncle
Globiform (round)
� Body has length about equal to width Rattail
� Caudal area is narrowed to posterior point
� Usually found in deep-sea
� Mostly scavengers
Odd-Shaped
� A few fish do not easily fit into a category
� Usually highly specialized fish

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FISH MOVEMENTS FOR SWIMMING
� Move by a variety of means
� Passive drift
� Burrow
� Walk
� Crawl
� Glide
� Fly
� SWIM !! �forward and backward
How Do Fish Swim?
� Undulations of body
� Movement of fins
� The water around the fish is relatively incompressible
� Fish �push off� from surrounding water
� Body bends from side to side and does not shorten
Lateral Flexures of Body
� Propel fish forward
� Body makes a propulsive wave posteriorly
� More waves = faster swimming
� Shape of body decreases drag (resistance to movement)
Swimming Modes of Fish
� Because of different fish body shapes there are different forms of body
movements for swimming
� Four distinct modes are found
� Anguilliform
� Subcarangiform
� Ostraciform
� Carangiform
Anguilliform Swimming

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� Found in flexible long-bodied fish like eels
� Whole body is flexed into lateral waves
� Also used by some shorter bodied fish when swimming slow
Carangiform Swimming
� Involves throwing the body into a shallow wave
� These fish usually have a long forked caudal fin
� Includes thunniform
� Fish with low drag
� Fastest of all fish
Subcarangiform Swimming
� Like Carangiform, with exceptions
� Undulate body less than one full wavelength
� Speeds greater than one body length per second
Ostraciform Swimming
� Only body flexing is at the caudal peduncle
� Can not generate speed
Swimming with fins
� Some fish can swim at high speed using only fin muscle movement
� Allows for coordinated movements

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29

30

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LECTURE NO. 5.
MOUTH POSITIONS
� Often tells the
� where and what
� of feeding
Four distinct mouth positions
� Superior
� Terminal
� Subterminal
� Inferior
Superior Oriented Mouth
� Mouth opening points upwards
� Surface oriented fish
� Usually feed on objects on the water�s surface
� Commonly found in oxygen poor water
� The surface layer tends to have the highest concentration of O2
Terminal Mouth
� Mouth is at the extreme anterior
� Feeding on what is directly in front
� Often predators
Subterminal Mouth
� Mouth is mostly ventral
� Bottom feeders
� Many also have barbels (whiskers)
� Many are scavengers or herbivores
Inferior Mouth
� Mouth is used to suck things off the bottom � Most are scavengers

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� Most are scavengers

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LECTURE NO. 6 SKELETON
There are two different skeletal types:
�the exoskeleton, which is the stable outer shell of an organism, and
the endoskeleton, which forms the support structure inside the body.
�The skeleton of the fish is either made of cartilage (cartilaginous
fishes) or bones (bony fishes).
�The main features of the fish, the fins, are bony fin rays and,
except the caudal fin, have no direct connection with the spine.
�They are supported only by the muscles.
�The ribs attach to the spine.
�Bones are rigid organs that form part of the endoskeleton of
vertebrates.
�They function to move, support,
�and protect the various organs of the body,
�produce red and white blood cells and store minerals.
�Bone tissue is a type of dense connective tissue.
�Because bones come in a variety of shapes
�and have a complex internal and external structure
�they are lightweight, yet strong and hard, in addition to fulfilling
their many other functions.
�Fish bones have been used to bioremediate lead from contaminated soil.

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LECTURE NO. 7.
FISH FINS
� Structure supports an independent evolutionary history of cartilaginous and
bony fishes
� Most fish have two sets of paired fins and four unpaired fins
� Fins are used to propel, stabilize and maneuver
Internal Support for Fins
� Supports have independent evolutionary history in bony & cartilaginous fish
� Fin rays are internal supports for fins
� Ceratotrichia (cartilaginous)
� Stiff, unbranched, unsegmented
� Lepidotrichia (bony fish)
� Flexible, branched, segmented
� True spines may occur that emerge into fins
Paired fins
� Pelvic fins
� Most variable in position
� Ancestral, = ventral, toward posterior
� Derived = thoracic
� Rarely in front of pectoral
� Pectoral fins

35
� Usually on sides
Pelvic Fin Placement
Pelvic Fin Modifications
Pectoral Fin Modifications
Dorsal & Anal Fins
� High degree of differences in size
� Dorsal varies in position considerably
� Some fish have more than one dorsal fin
� Dorsal may have
spinous and soft-rayed portions
Dorsal Fin Modifications
Caudal Fin
� Shape related to normal swimming speed
� Two general types
� Homoceral
� Upper & lower lobes about equal
� Vertebral column ends at peduncle
� Found in most bony fish
� Heteroceral
� Upper lobe significantly longer than lower
� Vertebral column extends into upper caudal fin
� Isoceral (considered heteroceral evolutionarily)
� Lacking lobes
Adipose Fin
� Fleshy dorsal appendage
� Lacking in many fish
� Between dorsal & caudal fins
� Lacks rays
� Function not well understood
Spines
� May be present or absent in fins
� Usually on dorsal, anal, & pectoral fins
� Common in many bony fishes
� Evolved many times independently
� Some also associated with poison glands

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Caudal Fins
�Heterocercal
�vertebral column extends into the upper lobe of the tail.
�Eg. Bowfins
�Amiidaehave an intermediate abbreviate heterocercalcaudal fin.
�Protocercal
�undifferentiated caudal fin
�vertebaeextends to the posterior end of the fish.
�Diphycercal
�similar to protocercal
�dorsal and anal fins joined with caudal fin at the posterior part of the
fish.
�This is thought to be a derived character
�Homocercal
�hypuralbones support most of the branched fin rays.
�Epuralbones turn upward and support the upper procurrentrays .
�Gephyrocercal–caudal fin can be 2olost –sunfishes (Molidae)
Types of caudal (tail) fin:
(A) - Heterocercal, (B) - Protocercal,
(C) - Homocercal, (D) - Diphycercal

37

38
LECTURE NO. 8.
FISH SCALES
� Type, size, and number tell a lot about a fish's way of life
� Evolved independently in cartilaginous and bony fish
� Scales offer a trade-off between protection and movement
� All fish scales are one of four types
� Some fish lack scales
Placoid Scales
� Found in cartilaginous fish
� Tooth-like structures
� Include basal plate containing some bone
� Have pulp cavity and dentin
� Outer layer is vitrodentin (similar to enamel)
� The spine of a sting ray is a modified placoid scale
Ganoid Scales
� Has a typical rhomboid shape
� Anterior peg-like extension overlapped by preceding scale
� One outer layer is bone
� Non-flexible
� Ganoine (enamel-like)
Cycloid Scales
� Round, flat, and thin
� Flexible bony layer
� Covered with epidermis

39
� Includes mucus glands
� Curculi (growth ridges) are present
� Enamel layer present
Ctenoid Scale
� Structure like cycloid
� Sometimes these two types are called elasmoid scales
� Have comb-shaped projections on posterior, called ctenii
� Improve swimming efficiency
� Have minute exposed spines
� Makes the fish feel rough
Cosmoid Scales
� Found only in extinct lobe-finned fish
� Contained layer of non-cellular cosmine
� Below cosmine was vascularized bone
� Living coelacanth may have simplified cosmoid scales
� No cosmine
Composition
�As with fish skin, the chemical composition of scales ispoorly known.
�About 41–84% is organic protein,
�Mostlyalbuminoids such as collagen (24%)
�and ichthylepidin (76%).
�Up to 59% is bone, mostly Ca3(PO4)2 and CaCO3.

40
LECTURE NO. 9.
FISH DENTITION
Agnathans (hagfish and lampreys)
� horny cones
� beneath cones are papillae of the mesoderm covered with ectoderm which
resemble the covered with ectoderm which resemble the dental papillae and
enamel organs although no calcification occurs
Gnathostomes (vertebrates with a jaw) Chondricthyes ( cartilagenous fishes)
� teeth are arranged in several rows
� when front row fall a new row takes their place
� some times triangular sharp as in the sharks
� sometimes flattened and arranged like a pavement for crushing as in rays.
� These teeth only represent the crowns of human’s teeth ‐ not
embedded in sockets except in the case of the teeth in the saw of the
saw‐ fish (Pristis).
� These teeth are largely composed of dentine, but they resemble bone and
fill up the whole pulp cavity.
Actinoptergyii (ray fin fishes)
� Continuously replaced , sometimes in blocks or rows (characids = sides
of a jaw)
� Variable no
teeth (strgeon)
to all bon •
Variable – no
teeth (st u
rgeon) to all
bon y plates in
the mouth
(monkfish)
� Hinged teeth pike and the hake where teeth
� Hinged teeth
� pike and the hake where teeth bend backward during the passage of

41
prey down the throat but are re‐ erected by elastic down the throat , but are re
erected by elastic ligaments.
Types of teeth
� Canine: large conical teeth often at the corners of the mouth corners of the
mouth
� Molariform – pavement like or molar like crushing teeth (rays
musselcracker )– hard crushing teeth (rays , musselcracker ) – hard prey
items eg. gastopods.
� Villiform– small fine teeth
� Cardiform– fine pointed teeth arrangged closely together
places for teeth
� Jaws
� Pharyngeal teeth – modified 6 th gill arch
� Gill rakers
� Mouth bones
Development
� Development of teeth similar to the development of scales development of
scales evolve from epidermal eruptions in the skin of the j aws j The basic
structure of a tooth consists of three main regions:
� 1. Enamel ‐ the surface layer of the tooth that is hard and protective
(1% protein = enamelin + 99% calcium p hos p hate pp (apatite) crystals).
Arranged in prisms perpendicular to dentines)
� 2 . Dentine ‐ makes up the bulk of the tooth (matrix of collagen and
hydroxyapatite crystals)
� 3. Pulp cavity ‐ contains the blood vessels and nerves that feed and
innervate the tooth
Teeth can vary in their permanence, their attachment and their structural their
attachment , and their structural differentiation.
� Polyphyodont‐ continuous succession of teeth throughout life (shark) ••
� Diphyodont‐ replacement of milk or Diphyodont‐ replacement of milk or
deciduous teeth by permanent teeth (mammals)
� Monophyodont‐ single set of teeth retained throughout life (whales,

42
marsupials) marsupials)
Attachment
� Acrodont‐ simplest teeth that Acrodont simplest teeth that have no roots
and may break off easily from jaw (fish and easily from jaw (fish and
amphibians) • Pleurodont‐ teeth attached by
� Pleurodont‐ teeth attached by one side to the inner surface of the jaw
bone (lizards) the jaw bone (lizards)
� Thecodont‐ teeth set into sockets and relatively immobile.
Structural differentiation:
� Homodont ‐ teeth essentially all alike
� Heterodont‐ teeth differentiated into a variety of uses

43
SOFT ANATOMY

44
TOPIC NO. 10.
ECOPHYSIOLOGY&BODY COMPOSITION OF
FISH
Topic no. 1 Ecophysiology
Ecophysiology ,environmental physiology or physiological ecology is a biological
discipline that studies the adaptation of an organism's physiology to environmental
conditions. It is closely related to comparative physiology and evolutionary
physiology.
The body composition of fish
Water
The main constituent of fish flesh is water, which usually accounts for about 80 per
cent of the weight of a fresh white fish fillet. Whereas the average water content of
the flesh of fatty fish is about 70 per cent, individual specimens of certain species
may at times be found with a water content anywhere between the extremes of 30
and 90 per cent.
The water in fresh fish muscle is tightly bound to the proteins in the structure in
such a way that it cannot readily be expelled even under high pressure. After
prolonged chilled or frozen storage, however, the proteins are less able to retain all
the water, and some of it, containing dissolved substances, is lost as drip. Frozen
fish that are stored at too high a temperature, for example, will produce a large
amount of drip and consequently quality will suffer. In the living fish, the water
content usually increases and the protein content decreases as spawning time
approaches; thus it is possible, with cod for example, to estimate the condition of
the fish by measuring the water content of the muscle.
In cod, the water content of the muscle is slightly higher at the tail than at the head;
this slight but consistent increase from head to tail is balanced by a slight reduction
in protein content.
Protein
The amount of protein in fish muscle is usually somewhere between 15 and 20 per
cent, but values lower than 15 per cent or as high as 28 per cent are occasionally
met with in some species.
All proteins, including those from fish, are chains of chemical units linked together
to make one long molecule. These units, of which there are about twenty types, are
called amino acids, and certain of them are essential in the human diet for the

45
maintenance of good health. Furthermore, if a diet is to be fully and economically
utilized, amino acids must not only be present but must also occur in the correct
proportions. Two essential amino acids called lysine and methionine are generally
found in high concentrations in fish proteins, in contrast to cereal proteins for
example. Thus fish and cereal protein can supplement each other in the diet. Fish
protein provides a good combination of amino acids which is highly suited to
man’s nutritional requirements and compares favourably with that provided by
meat, milk and eggs.
Fat
Taking all species into account, the fat content of fish can vary very much more
widely than the water, protein or mineral content. Whilst the ratio of the highest to
the lowest value of protein or water content encountered is not more than three to
one, the ratio between highest and lowest fat values is more than 300 to one.
The term fat is used for simplicity throughout this leaflet, although the less familiar
term lipid is more correct, since it includes fats, oils and waxes as well as more
complex, naturally-occurring compounds of fatty acids.
There is usually considerable seasonal variation in the fat content of fatty fish; for
example a starved herring may have as little as ½ per cent fat, whereas one that has
been feeding heavily to replenish tissue may have a fat content of over 20 per cent.
Sardines, sprats and mackerel also exhibit this seasonal variation in fat content. As
the fat content rises, so the water content falls, and vice versa; the sum of water
and fat in a fatty fish is fairly constant at about 80 per cent. Although protein
content falls very slightly when the fat content falls, it nevertheless remains fairly
constant, somewhere between 15 and 18 per cent.
The fat is not always uniformly distributed throughout the flesh of a fatty fish. For
example in Pacific salmon there may be nearly twice as much fat in muscle from
around the head as there is in the tail muscle.
In white fish of the cod family, the fat content of the muscle is always low, usually
below 1 per cent, and seasonal fluctuations in fat content are noticeable mainly in
the liver, where the bulk of the fat is stored.
The minor components of fish muscle
Carbohydrates
The amount of carbohydrate in white fish muscle is generally too small to be of
any significance in the diet; hence no values are given in the tables. In white fish
the amount is usually less than 1 per cent, but in the dark muscle of some fatty
species it may occasionally be up to 2 per cent. Some molluscs, however, contain

46
up to 5 per cent of the carbohydrate glycogen.
Minerals and Vitamins
These include a range of substances widely different in character that must be
present in the diet, even if only in minute quantities, not only to promote good
health but also to maintain life itself.
Although fish is very unlikely to be the only source of an essential mineral in the
diet, fish does provide a well balanced supply of minerals in a readily usable form.
The table of mineral constituents of fish muscle gives values averaged from a large
number of species and is intended to serve only as a rough guide. It would be
impracticable in this short note, and of limited value, to give a detailed analysis for
individual species.
Composition tables for fish often include a value for total ash. Since ash consists
largely of a number of different minerals, and the total rarely exceeds 1-2 per cent
of the edible portion, this figure has also been omitted, except from the table of fish
products.
Vitamins can be divided into two groups, those that are soluble in fat, such as
vitamins A, D, E and K, and those that are soluble in water, such as vitamins B and
C. All the vitamins necessary for good health in humans and domestic animals are
present to some extent in fish, but the amounts vary widely from species to species,
and throughout the year.
The vitamin content of individual fish of the same species, and even of different
parts of the same fish, can also vary considerably. Often the parts of a fish not
normally eaten, such as the liver and the gut, contain much greater quantities of
oil-soluble vitamins than the flesh; the livers of cod and halibut for example
contain almost all of the vitamins A and D present in those species. In contrast, the
same two vitamins in eels, for example, are present mainly in the flesh.
Water-soluble vitamins in fish, although present in the skin, the liver and gut, are
more uniformly distributed, and the flesh usually contains more than half the total
amount present in the fish. The roe, when present, is also a good source of these
vitamins.
In general the vitamin content of white fish muscle is similar to that of lean meat
and, with the exception of vitamin C, can usually make a significant contribution to
the total vitamin intake of man and domestic animals.
The mineral and vitamin content of fish is not markedly affected by careful
processing or by preservation, provided storage is not very prolonged.
Extractives
These substances are so called because they can easily be extracted from fish flesh

47
by water or water-based solutions. Unlike the proteins, substances in this group
have comparatively small molecules; the most important extractives in fish include
sugars, free amino acids, that is free in the sense that they are not bound in the
protein structure, and nitrogenous bases, which are substances chemically related
to ammonia. While many of these extractives contribute generally to the flavour of
fish, some of them, known as volatiles, contribute directly to the flavours and
odours characteristic of particular species; as the name suggests, volatiles are given
off from the fish as vapours. Most of the extractives are present at very low
concentrations but, because of their marked flavour or odour, are nonetheless
important to the consumer. Detailed analyses of these substances have not been
given because of the large variation existing both between and within species. An
additional complication is the way in which the concentrations of these compounds
change during storage and spoilage.
Factors affecting the composition of fish
The composition of a particular species often appears to vary from one fishing
ground to another, and from season to season, but the basic causes of change in
composition are usually variation in the amount and quality of food that the fish
eats and the amount of movement it makes. For example, fish usually stop feeding
before they spawn, and draw on their reserves of fat and protein. Again, when fish
are overcrowded, there may not be enough food to go round; intake will be low
and composition will change accordingly. Reduction in a basic food resource,
plankton for example, can affect the whole food chain. An example of how
abundance of food supply can markedly change the composition of a species is
shown by the sheepshead, an American freshwater fish: when taken from certain
small lakes that were overstocked, the sheepshead had an average fat content of 1
per cent, compared with 6-10 per cent for those taken from rivers or lakes where
food was plentiful.

48
LECTURE NO. 11
WEBERIAN APPARATUS
�Fishes of the superorder Ostariophysi possess a structure called the Weberian
apparatus ,
�a modification which allow them to hear better.
�This ability which may well explain the marked success of otophysian fishes.
�The apparatus is made up of a set of bones known as Weberian ossicles ,
�a chain of small bones that connect the auditory system to the swim bladder of
fishes.
�The ossicles connect the gas bladder wall with Y-shaped lymph sinus that abuts
the lymph-filled transverse canal joining the sacculi of the right and left ears.
�This allows the transmission of vibrations to the inner ear.
�A fully functioning Weberian apparatus consists of the swim bladder,
�the Weberian ossicles, a portion of the anterior vertebral column, and some
muscles and ligaments.

49
LECTURE NO. 12SKIN
�The epidermis of fish consists entirely of live cells,
�with only minimal quantities of keratin in the cells of the
superficial layer.
�It is generally permeable.
�The dermis of bony fish typically contains relatively little of the
connective tissue found in tetrapods.
�Instead, in most species, it is largely replaced by solid, protective
bony scales.
�Apart from some particularly large dermal bones that form parts
of the skull,
�these scales are lost in tetrapods, although many reptiles do have
scales of a different kind, as do pangolins.
�Cartilaginous fish have numerous tooth-like denticles embedded
in their skin, in place of true scales.
�Sweat glands and sebaceous glands are both unique to mammals, but
other types of skin glands are found in fish.
�Fish typically have numerous individual mucus-secreting skin cells that
aid in insulation and protection,
�but may also have poison glands, photophores, or cells that produce a
more watery, serous fluid.
�Melanin colours the skin of many species, but in fish the epidermis is
often relatively colourless.
�Instead, the colour of the skin is largely due to chromatophores in the
dermis, which, in addition to melanin, may contain guanine or carotenoid
pigments.
�Many species, such as flounders, change the colour of their skin by
adjusting the relative size of their chromatophores.[12]

50
LECTURE NO. 13. SWIMBLADDER
� Major organ for buoyancy control
� Allow for precise control of total body specific gravity
� Normally 5% of marine fish
body, 7% of freshwater body
Types of Swimbladders
� Physostomous
� Have a connection between
the swimbladder and gut
(Pneumatic Duct)
� Mostly ancestral, soft-rayed
teleosts
� Physoclistous
� No connection between
swimbladder and gut
� Swimbladder is a closed
structure
Physostomous Swimbladders
� Fish must swallow air to
deliver it to the swimbladder
� Requires these fish to live in
shallow water
� They cannot take in enough air
to be buoyant at deep water and
actually move to deep water
Control of Physostomous
Swimbladder
� Air is controlled by a
pneumatic sphincter muscle
� Deflation is a gas-spitting
reflex (gas-puckerflex)
Physoclistous Swimbladder
� Swimbladder is inflated via
circulatory system

51
� Rete mirabile (wonderful net)
� Gas gland
� Fish are able to live away from the surface
Rete Mirabile
� Blood flows through rete capillaries
� Materials enter the gas gland from the capillaries
� Gas gland tissues produce acid
� Glycolitic transformation of glucose (produces HCO3-)
� HCO3- dehydrates to CO2
Filling the Swimbladder
� CO2 diffuses from gas gland into swimbladder
� Partial pressure from depth of fish regulates the amount of gas that diffuses
Modified Swimbladders
� Many size modifications occur
� Some fish have more than one swim bladder
� Often fish with great vertical movements
� Allows them to gain or lose air more quickly
Bottom Dwellers
� Swimbladder is not needed
� Reduced
� Vestigial
� Absent
� Neutral buoyancy is not an advantage
� Negative buoyancy is desired
Species Living in Flowing Water
� Usually have reduced swim bladders
� Less buoyancy helps them to maintain a given area
� Their buoyancy requirement is met by other means than the swimbladder
Mola mola
� Has no swimbladder
� Commonly a surface dweller � sometimes floats on the surface
� Large amounts of body fluid that are about ½ the specific gravity of seawater

52
LECTURE NO. 14
PHOTOPHORES
�Photophores are light-emitting organs which appears as
luminous spots on some fishes. The light can be produced from
compounds during the digestion of prey, from specialized
mitochondrial cells in the organism called photocytes, or
associated with symbioticbacteria, and are used for attracting
food or confusing predators.
KIDNEYS
�The kidneys of fish are typically narrow, elongated organs, occupying a
significant portion of the trunk.
�They are similar to the mesonephros of higher vertebrates
(reptiles, birds and mammals).
�The kidneys contain clusters of nephrons, serviced by collecting ducts
which usually drain into a mesonephric duct.
�However, thesituation is not always so simple.
�In cartilaginous fish there is also a shorter duct which drains the
posterior (metanephric) parts of the kidney, and joins with the duct at the
bladder or cloaca.
�Indeed, in many cartilaginous fish, the anterior portion of the kidney may
degenerate or cease to function altogether in the adult.[12]
�Hagfish and lamprey kidneys are unusually simple.
�They consist of a row of nephrons, each emptying directly into the
mesonephric duct.

53
LECTURE NO. 15
BLOOD COMPOSITION
• � Erythrocytes
• � Leukocytes
• � Structure of Hemoglobin
•
• Formation of Fish Blood Cells
• � Formed from hemocytoblast
• � Blood forming site differs
• � Agnatha
• � Mesodermal envelope around gut in hagfish
• � Fatty tissue dorsal to nerve cord in lampreys
• � Elasmobranchs
• � Leydig organ (near esophagus)
• � Epigonal organ (around gonads)
• � Spleen
•
• Formation of Fish Blood Cells continued
• � Teleosts
• � Kidney
• � Spleen
• � Cranium
• � Thymus
• � Fish bone has no marrow
•
• Erythrocytes
• � Most abundant fish blood cells
• � Nucleated
• � Size range exists (elasmobranchs usually larger, but fewer)
• � More active species have more red blood cells
•
• Hemoglobin of Fish Erythrocytes
•
• � Primary means for transporting oxygen
• � In some fish up to 15% may be in plasma
• � A few fish have no hemoglobin (rare situation)

54
• � Environmental oxygen high
• � Low metabolic requirements
• � Special cardiovascular adaptations
•
• Fish Hemoglobin Characteristics
• � Structure is different in different fish
• � Monomeric
• � Single-heme peptide molecules
• � Much like myoglobin
• � Found in Agnatha
• � Tetrameric
• � Four peptide chanis
• � May differ in many features
• � Composition of amino acids
• � Affinity for oxygen
• � Elecrophoretic ability
• � Some salmonids have up to 18 different hemeglobins

55
•
• Having Different Hemoglobin Types
• � Different Hemoglobins have different responses to temperature and
oxygen absorption
• � Allows fish to deal with changing conditions
• � Important for migratory species
• � Some fish gain or lose types as they age
•
• Blood Oxygen Affinity
• � pH
• � Decreasing pH decreases affinity
• � Often associated with carbon dioxide
• � Carbon dioxide
• � Increase in CO2 drives off O2 (Bohr effect)
• � Decrease in blood pH magnifies Bohr effect
• � Temperature
• � Increase in temperature depresses oxygen affinity and capacity
• � Results in fish having narrow temperature tolerances
• � Organic phosphate
• � ATP depresses O2 affinity
• � Urea increases O2 affinity
•
• Leukocytes
• � Less abundant than erythrocytes
• � Provide a mechanism for blood clotting
• � Rid the body of foreign materials
• � Several different types
•
• Lymphocytes
• � Can vary in size
• � Cell dominated by nucleus
• � Important for immune system via antibody production
• � There may be some phagocytic activity
•
• Monocytes
• � Cell outline may be quite irregular
• � Phagocytes of foreign particles
• � Attracted to foreign substances

56
• � Use pseudopods to engulf antigens
•
• Granulocytes
• � Leukocytes with cytoplasmic granules
• � Neutrophil
• � Migrate to sites of bacterial infection
• � Phagocytic or bacteriocidal
• � Basophil
• � Not found in all fish
• � Phagocytic
• � Eosinophil
• � phagocytic
•
• Non-Specific Cytotoxic Cells
• � Equivalent to natural killer cells
• � Lyse tumor cells
• � Lyse protozoan parasites
•
• Thrombocytes
• � Function in blood clotting
• � Cytoplasm spreads into long threads
• � Cell shape varies, but often has spikes
•
•
•
•
•
•
•
•
•
•

57
LECTURE NO. 16.
FISH MUSCLE
� In almost all fish, the large muscles of the body and tail comprise the
majority of the body mass, although many other muscles are associated with the
head and fins.
� The body muscles are divided vertically along the body length into sections
called the myomeres (or myotomes), which are separated by sheets of
connective tissue.
� The myomeres are shaped like a W on its side, so that they fit into one
another like a series of eones.
� The myomeres on the right and left halves of the body are separated by a
vertical septum.
� A horizontal septum separates the muscle masses on the upper and lower
halves of the body.
� The upper muscles are called the epaxial muscles and the lower muscles the
hy-paxial muscles.

58
� On inspection, fish muscles can often be divided into red (slow), white (fast),
and pink (intermediate) müscle
Muscle types
� Fish have the same three basic types of muscles as other vertebrates:
skeletal, smooth, and cardiac.
� Skeletal: Voluntary, used for locomotion, comprises the majority of the
fish’ s muscle mass.
� Smooth: Involuntary such as intestine, many organs, and the circulatory
system.
� Cardiac: Heart
� On inspection, fish muscles can often be divided into red (slow), white (fast),
and pink (intermediate) müscle
Skeletal Fish Muscle
� Essentially three types of fish muscle: red, white, pink.
� Red muscle (oxidative): Highly vascularized, myoglobin containing tissue
used during sustained swimming. Small diameter and high blood volume = rich
O2 supply! Presence leads to strong flavor in some fishes (tuna).
� White muscle (glycolytic): Little vascularization. Used during “burst”
swimming. Large diameter fibers.
� Pink muscle: This one is sort of in between red and white. Serves in
sustained swimming, but not to the extent that red muscle is used.

59
•
•
•
•
•
•
•
•

60
LECTURE NO. 17
FISH DIGESTIVE SYSTEM
Esophagus
� Usually short & distensible
� Many fish swallow large objects
� For all the teeth, there is very little chewing
� Walls have circular & longitudinal muscles
� Most swallowing is by esophagus
� Taste buds
� Gastric glands in some fish
Modifications of Esophagus
� Butterflyfish
� Muscular sacs lined with teeth
� Grind & crush food in esophogeal sacs
� Some fish have the esophagus modified for respiration
Stomach
� Differs greatly depending on diet
� Various shapes
� Bag-like
� U-shaped
� V-shaped
� Stomach is absent in some fish
� Lampreys, hagfish, minnows, & others
Intestine
� Length is quite variable
� Corresponds to amount of indigestible material in diet
� Carnivores � short
� Herbivores � several times body length
� Some fish have a spiral intestine
� Increases absorptive surface

61
Modifications of Intestine
� Parasitic fish like lampreys
� Intestine is very thin and
expandable
� Hagfish
� Intestine with extensive
folding
� Ingest large food
� No stomach
Cloaca
� Some fish have a
posterior gut that is a
common canal for urinary
& reproductive systems
� Sharks

62
� Rays
� lungfish
Digestive Accessory Organs
� Organs associated with the intestine
� Pyloric caeca
� Liver
� Pancreas
� Swimbladder (in some fish)
� Spleen (associated but not digestive)
Pyloric Caeca
� Attaches beyond pyloric end of stomach
� One to many blind sacs
� Absent in some fish
� Functions
� Digestion
� Absorption
Liver
� Very large in all fish
� Up to 30% of shark body mass
� Lies over or surrounds the stomach
� Most commonly bi-lobed
� Most fish have bile duct & gall bladder
� Function
� Bile secretion
� Glycogen storage
� Other biochemical processes
Pancreas
� Diffuse tissue in some fish
� Combined with liver in some derived fish (hepatopancreas)
� Hagfish have several pancreatic ducts that empty into bile duct
� Secretes enzymes & insulin
Spleen
� Usually on or behind stomach

63
� Function
� Red blood cell formation
� Destruction of old blood cells
� Agnatha have diffuse spleenlike tissue
� Lungfish lack a spleen
Digestion in Fish
� Breakdown by acidic secretions & enzymes
� Many enzymes
� Many food differences between species
� Most digestion starts in stomach when present
Guidelines for Rate of Digestion
� Carnivores have slow food passage
� 14-32 hours
� Motility is very slow
� Herbivores pass more food faster
�<3 � 8 hours
� A few species use fermentation for up to 20 hours
Absorption
� Much the same as for mammals
� Diffusion
� Membrane transport proteins
Metabolism and Nutrition
� Different species need different amounts of nutrition because there is great
variation in metabolism
�General rule: Metabolism is directly influenced by temperature
Physiology of Digestion
Different fishes have differernt mechanisms to digest
their food.

64
In all fishes, their is no digestion in buccal cavity
which lacks salivary glands.
Their food then moves down the oesophagus
through the wave of muscular contractions called
peristalsis.
Their is no digestion in the stomach.
The gastric juice in stomach contains pepsin and
hydrochloric acid.
Which converts proteins into peptides and
polypeptides.
Bile makes the semidigested food alkaline in
intestine while pancreas secretes trypsinogen,
amylase and lipase for digestion of proteins, starches
and fats, respectively.
Scroll valve or typhlosole in the intestine of sharks
serves to retard movement of food and increases
surface area for absorption of the products of
digestion manyfolds.

65
FEEDING BEHAVIOUR IN FISHES
Most fish feed in their natural environment, the larger fish eating the smaller ones,
and the smallest sea creatures feeding on marine plants. A fish's mouth gives many
clues about its feeding habits. Large, strong teeth indicate a diet of shellfish or
coral; pointed teeth belong to a hunting fish; and a large mouth that is open while
the fish swims is that of a filterer. Some species can also trap food that lives
outside the water: trout, for example, hunt flies.
Predators
These are fish that feed on other species. They have teeth or fangs that help them to
wound and kill their prey or to hold it fast after the attack. Predators use their sight
to hunt, although some nocturnal species such as moray eels use their senses of
smell and touch and those of their lateral line. All predators have highly evolved
stomachs that secrete acid to digest meat, bones, and scales. Such fish have a
shorter intestinal tract than herbivorous species, so digestion takes less time. e.g.
PIRANHA; Pygocentrus sp
Filterers
Some species have evolved to the point of being able to take from the water only
those nutrients they need for feeding. They filter the nutrients out using their
mouths and gills. These species include whale sharks (Rhincodon typus), herring
(Clupea sp.), and Atlantic menhaden (Brevoortia tyrannus).
Symbiosis
is the interaction between two organisms that live in close cooperation. One type of
symbiosis is parasitism, in which one organism benefits and the other is harmed.
An example of a parasite is the sea lamprey (Petromyzon marinus), which sticks to
other fish and sucks their body fluids to feed itself. Another type of symbiosis is
commensalism, in which one organism benefits and the other is not harmed. An
example is the remora (Remora remora), or suckerfish, which sticks to other fish
using suction disks on the end of its head.
Grazers
This group of fish eats vegetation or coral in small bites. Parrotfish (Scaridae) have
a horny beak made of fused teeth. They scrape the fine layer of algae and coral that
covers rocks and then crush it into powder using strong plates in the back of the
throat.

66
Suckers
Species that live in the depths, such as sturgeons (Acipenseridae) and suckerfish
(Catostomidae), spend their days sucking the mud on the seafloor. When they are
cut open, large amounts of mud or sand are found in the stomach and intestines.
Digestive mechanisms process all this material and absorb only what is needed.
DIFFERENCES
Grazers This group of fish eats vegetation or coral in small bites. Parrotfish
(Scaridae) have a horny beak made of fused teeth. They scrape the fine layer of
algae and coral that covers rocks and then crush it into powder using strong plates
in the back of the throat. CORAL Parrotfish feed on corals. WHALE SHARK
Rhincodon typus
Carnivorous fish eat all sorts of species, even though their basic diet consists of
meat. They have terminal-type mouths, muscular stomachs, and short intestinal
tracts. Herbivores feed on aquatic vegetation. They have a long intestinal tract
compared with other fish.

67
LECTURE NO. 18
RESPIRATORY SYSTEM
�Efficient O2 uptake is vital to fish because of its low water solubility.
�Solubility decreases with increased temperature & salinity!
�Also, metabolic rate (demand for O2 ) increases as temperature rises. (How
does this affect nutrition?)
Gills
�Gills are the main site of gas exchange in almost all fishes.
�The gills consist of bony or stiffened arches (cartilage) that anchor pairs of
gill filaments.
�Numerous lamellae protrude from both sides of each filament and are the
primary sites of gas exchange.
�Microscopic gill structure: showing gill filament and lamellae (Red blood
cells evident.)
�How can fish remove 80 - 90% of O2 available from water?
�Short diffusion distance at gill site
�Large surface area for diffusion at gill site
�Counter current exchange of gases at gill site
�Large volume of water passes over gills
•
Oxygen Exchange in Fish
�Fish employ the countercurrent system to extract O2 from the water.
�This system moves water flowing across the gills, in an opposite direction to
the blood flow creating the maximum efficiency of gas exchange.
Countercurrant* Close-up!
�Blood flow through lamellae is from posterior to anterior.
�Water flow over lamellae is from anterior to posterior.
�Counter-current allows for diffusion from high O2 in water to low O2 in blood
across entire length of lamella.
�When he blood and water flows in the same direction, the co-currentsystem,
it will initially diffuses large amounts of oxygen but the efficiency reduces

68
when the fluids start to reach equilibrium.
Let’s Do the Math...
�4gill arches on each side of body
� 2rows of gill filaments on each arch (demibranchs)
� 100‟s filaments per demibranch - closely spaced
�1000‟slamellae per gill filament
� gill area = 10 to 60 times that of body surface area, depending on species!
�HUGE potential to extract Oxygen from water!
Auxiliary Respiratory Structures
�Skin - diffusion of oxygen from water into dense network of capillaries in
skin (eels), Thin skin (larval fish) supplies 50% of O2 needed.
�Swim bladder - vascularized physostomous swim bladders (gars)
�Lungs - modified swim bladder (lungfishes)
�Mouth - vascularized region in roof of mouth (electric eel, mudsuckers)
�Gut - vascularized stomach or intestinal wall (armored catfish, loaches)
Branchial vs. Ram Ventilation
Branchial
�Mouth
�Pharynx
�Operculum
�Branchiostegals (filaments, lamella)
Ram
�Uses same parts, but not the pumping energy required. Sharks primarily.
Once swimming speed is achieved...no need to actively vent buccal cavity.
However, this can only be used consistently by strong swimmers (sharks, tuna).

69

70
Physiology of respiration.
When the water pass over the gills, the gill lamella extracts oxygen from it through
its vast number of blood vessels.
Each gill lamella has an extensive system of sinusoids which recieve blood from an
afferent brancial artery and pass it on to an efferent brachial artery.
During the passage of blood through this network, it becomes oxygenated.
This oxygen passes by diffusion thin membranous and permiable walls of
capillaries into blood.
At the same time carbondioxide of venous blood passes out diffusion into outgoing
water current.
The oxygenated blood circulates through the body, its oxygen is used by tissues to
oxidise food-stuffs and carbondioxide thus formed enters into the blood which
again becomes venous.

71
LECTURE NO. 11.
FISH CIRCULATORY SYSTEM
� Primary circulation
� Closed system
� Heart
� Arteries
� Capillaries
� Veins
� Secondary circulation
� Collects blood that is outside the primary
� Originally thought to be lymphatic
� No lymph or lymph nodes
Divisions of Primary Circulation
� Branchial circulation
� Blood from heart through gills
� Systemic circulation
� Blood from gills to body to heart
� Blood flow is continuous from heart, to lungs, to body, back to heart
Proximity of Heart & Gills
Exceptions to Normal Circulation
� Hagfish have accessory inline hearts
� Lungfish have pulmonary circulation
� There are also many small adaptations in some species
Structure of the Fish Heart
� Four chambered heart
� All four chambers are in line
� The heart pumps only venous blood
� Except for a few air breathing fish, all blood is pumped to the gills
Chambers of the Fish Heart
� (1) Sinus venous
� Collects blood from venous ducts

72
� (2) Atrium
� Accelerates blood flow
� (3) Ventricle
� Large muscled chamber
� Provides propulsive flow for circulation
� (4) Bulbus arteriosus (bony)
Conus arteriosus (cartilagenous)
� Changes blood from a pulse to continuous flow
Conus Arteriosus vs. Bulbus Arteriosus
� Conus Arteriosus
� Contractile
� Cardiac muscle
� More than one valve
� Bulbus Arteriosus
� Elastic
� Mostly connective tissue
� One valve dividing it from ventricle
Regulation of the Fish Heart
� Self-regulating
� Timing can be modified by
brain
� Pace is set by pacemaker
cells
� Many areas show
pacemaker activity
The Hagfish Heart
� Most primitive
� Sinus venous well
developed
� Divided into two parts to
receive different veins
� Bulbus arteriosus
� Have 3 additional hearts
� Caudal heart in head

73
� Brachial heart near gills

74
� Portal heart � pumps blood through liver
Lamprey Heart
� Largest of fish hearts
� Atrium overlies ventricle
� Bulbus arteriosus
� Right common cardinal vein empties into atrium
Elasmobranch Heart
� Conus arteriosus
� Sinus venosus with almost no cardiac muscle
� Ventricle has two muscle layers
� Compacta = compact outer layer
� Spongiosa = inner layer
Teleost Heart
� Variation exists across the group
� Sinus venous is thin walled
� Most have bulbus arteriosus
� Some have conus arteriosus (usually more primitive)
Lungfish Heart
� Atrium is divided into two parts by an incomplete septum
� Functional 3 chamber heart
� Like amphibians
� Right atrium larger than left
� Right = deoxygenated from sinus venosus
� Left = oxygenated from pulmonary vein

75
LECTURE NO. 20
CENTRAL NERVOUS SYSTEM
� Great variation in fish brain morphology
� Size varies
� Senses account for most size variation
� Range from 0.1% of body weight (coelacanth) to over 1% (Mormyridae)
Brain Development
� First develops into 3 sections
� Forebrain = prosencephalon
� Midbrain = mesencephalon
� Hindbrain = rhombencephalon
Brain Structure
� Cerebrum = Telencephalon
� Thalamus = Diencephalon
� Tectum = Mesencephalon
� Cerebellum & Pons = Metencephalon
� Medulla Oblongata = Myelencephalon
� The major portion of the telencephalon deals
with olfaction
� Diencephalon
� Nerve tracts
� Pituitary
� Pineal gland
� Light sensitive
� Parapineal gland
� Optic chiasm crosses externally
� Tectum
= optic tectum
= midbrain
= mesencephalon
� Optic lobes are prominent feature
� Size of optic lobes is associated with how visual the fish is
� Metencephalon
� Cerebellum is involved in muscle coordination

76
� Nerve conduction tracts in pons
� Also some autonomic reflex centers
� Metencephalon
� Medulla has many reflex centers
� Example = startle reflex
There is Great Variation in Fish Brains
Freezing Resistance in Fish
� Most fish are not subject to freezing if their environment does not freeze
� Body fluids are hyperosmotic or isoismotic
� Marine teleosts are a different story
� Environment has a higher salt concentration than body
� Their environment could stay unfrozen, but their body could freeze
Dealing with Below Freezing Temperatures
� A few teleosts increase osmolality
� Example: rainbow smelt
� Increases gycerol and urea concentrations
� Depresses body freezing point
� Some fish develop antifreeze
� Glycopeptides or Peptides
� Interferes with ice crystal growth
� There are still limits
� Best case is not quite to �2 degrees C
Adaptations to Living in Extreme Cold
� Antifreeze
� Aglomeular kidney
� Conserves instead of filters glycopeptides
� Syntheis of antifreeze peptides in liver
� Also some in skin, scales, & gills
Acid-Base Balance
� Homeostasis requires a very narrow range
� Changes in temperature or CO2 content can alter blood pH
Ways to Maintain Proper pH
� A large amount of CO2 can bind to Hemoglobin

77
� Many heme groups are not filled with O2
� Most CO2 in red blood cells is then easily converted to HCO3-
� CO2 easily leaves blood plasma & diffuses at gills
Ways to Maintain Proper pH
� Hyperventilating washes blood of CO2
� Used when there is an excess accumulation
� Bicarbonate also acts as a buffer in blood
� Maintenance of the correct pH restricts most fish to a narrow, preferred water
pHBUOYANCY & THERMAL REGULATION
� Why do we study these two functions together
� Swimbladders of some fish and heat-exchange organs of others are
morphologically very similar
� Both deal with exchange across blood vessels
Buoyancy
� Fishes have two means of maintaining buoyancy
� Neutral buoyance
� Regulation by swimbladder
Neutral Buoyancy
� Many fish are functionally weightless in water
� This allows them to save energy while staying in a certain area
What is Required for Neutral Buoyancy?
� Specific gravity must equal that of surroundings
� Fresh water sp. gr. = 1
� Salt water sp. gr. = 1.026
� Different regions may have slight specific gravity differences due to dissolved
materials
Strategies to Maintain Neutral Buoyancy
� Body made of large quantities of low density compounds
� Fins are shaped and angled to generate forward lift
� Reduction of heavy tissues like bone
� Having a swimbladder filled with an appropriate amount of air

78
Low Density Bodies
� Many fish have large quantities of lipids
� Specific gravity < 1
� Large livers filled with squalene
� Hydrocarbon sp.gr. 0.8
� A few fish have trigliceride oils in bones
Fins Designed for Lift
� Leading edges of fins help maintain position
� Small amount of energy gives large amount of lift
� Also, body drag is eliminated by shape of fins and body
Reduction of Heavy Tissue
� Bones are thin
� Living in water does not require as much support
� Sp. gr. of bone = 2.0
� Cartilage is less dense than bone
� Sp. gr. = 1.1
� Many fish do not have a bony skeleton
Oddities for Maintaining Neutral Buoyance
� Deepsea Acanthonus armatus has enlarged cranial cavity filled with �light�
water
� Oilfish, Ruvettus sp. have around 15% of body weight in was esthers

79
TOPIC NO. 21
HORMONES
The endocrine system Ongoing research has rapidly expanded knowledge of the
endocrine systems of fi shes, and it is not surprising that there is great diversity in
the hormones and their functions among various groups of fi shes. Therefore, it is
not possible given the space available to provide a complete synopsis of f i sh
endocrine tissues, their hormones, and their effects. Instead, we will provide a brief
summary of some of the hormones important to homeostasis, but will not address
the many other physiological functions of hormones in fishes. Many endocrine
functions are ultimately controlled by the hypothalamus of the brain regulating the
many functions of the pituitary which, in turn, helps regulate many other endocrine
tissues in the body. The pituitary has two main functional regions. The posterior
pituitary , or neurohypophysis , is continuous with the hypothalamus and consists
primarily of the axons and terminals of neurons that originate in the hypothalamus.
The anterior pituitary , or adenophypophysis , lies in contact with the posterior
pituitary, and in the actinopterygians the tissues fuse. The hypothalamus controls
the anterior pituitary by releasing hormones delivered via blood vessels in some fi
shes, such as chondrichthyans, or by direct innervation as seen in some
actinopterygians. Some fi shes also have an intermediate lobe of the anterior
pituitary, and elasmobranches have a ventral lobe below the anterior pituitary
(Takei & Loretz 2006).
POSTERIOR PITUITARY
The posterior pituitary is primarily the storage and release site of chemical
messengers of the hypothalamus. Neuroendocrine cells (neurons that function as
endocrine cells) begin in the hypothalamus and extend into the neurohypophysis
where they release their chemicals, some of which are hormones that are released
into blood vessels and trigger effects elsewhere in the body. Vasopressin (also
called arginine vasotocin), for example, plays an important role in osmoregulation
(Takei & Loretz 2006). Other chemicals released by the posterior pituitary regulate
the function of cells of the adjacent anterior pituitary and intermediate lobe, and
are sometimes referred to as releasing factors or releasing hormones. Some of these
diffuse to the intended target cells in immediately adjacent sections of the pituitary,
whereas others travel the short distance to their target cells via blood vessels.
ANTERIOR PITUITARY
The anterior pituitary, largely under the control of the hypothalamus,

80
manufactures and releases hormones that control many physiological functions
elsewhere in the body, including many other endocrine tissues. For example, the
anterior pituitary releases adrenocorticotropic hormone (ACTH), which infl
uences the production and release of cortisol from the interrenal tissue, and
thyroid-stimulating hormone (TSH), which stimulates the thyroid gland to release
thyroxin, gonadotropins (which stimulate the gonads), and growth hormone (GH)
which affects various tissues throughout the body (Takei & Loretz 2006).
Fishes are the only jawed vertebrates known to possess a caudal neurosecretory
system. Located at the caudal end of the spinal cord, this region of neuroendocrine
cells, the urophysis , is most highly developed in the ray-fi nned fi shes and
produces urotensins that help control smooth muscle contraction, osmoregulation,
and the release of pituitary hormones (Takei & Loretz 2006).
THYROID GLAND
The thyroid tissue of most fishes is scattered as small clusters of cells in the
connective tissue of the throat region, as opposed to the rather discrete gland found
in tetrapods. When stimulated by TSH from the anterior pituitary, these cells
produce thyroxin , which plays an important role in growth, development, and
metabolism in many fishes. Thyroxin is quite important in development, including
the sometimes extreme morphological and physiological changes associated with
metamorphosis – such as the transformation of fl ounder from larvae with an eye
on each side of the head to flatfish with both eyes on one side of the head. It also
initiates seaward migratory behavior and the accompanying osmoregulatory
adaptations of juvenile salmonids during their seaward spawning migration (Takei
& Loretz 2006; see Chapter 10, Complex transitions: smoltif i cation in salmon,
metamorphosis in flatfish). Maintaining proper calcium balance, including
regulating calcium uptake at the gills, involves several hormones, including
stanniocalcin from the corpuscles of Stannius embedded in the kidney, calcitonin
produced by the ultimobranchial bodies in the back of the pharynx, and prolactin
and somatolactin from the anterior pituitary (Takei & Loretz 2006).
ADRENAL GLAND
The interrenal tissues of fishes are homologous with the distinct adrenal glands of
the tetrapods, but are somewhat scattered in their location. The interrenal consists
of two different types of cells, each of which produces different hormones. The
chromaffi n cells are located in the wall of the posterior cardinal vein in the
pronephros of agnathans, along the dorsal side of the kidney in elasmobranchs, and
in the anterior, or head, kidney of teleosts. Chromaffi n cells produce and release
the catecholamines epinephrine (adrenaline) and norepinephrine (noradrenaline)

81
(Takei & Loretz 2006). The catecholamines maintain or enhance the delivery of
oxygen to body tissues by increasing gill ventilation rates and blood fl ow, and
increasing oxygen transport capability by increasing the release of red blood cells
from the spleen and increasing the intracellular pH of red blood cells (Hazon &
Balment 1998). This increased blood fl ow to the gills may lead to increased ion
exchange, which may explain why stressed fi shes can experience signifi cant
osmoregulatory imbalances (discussed later in this chapter).
The second group of interrenal cells is that of the steroid producing cells, located
primarily in the pronephric or head kidney region. These manufacture and release
corticosteroids, including cortisol , which is important in energy metabolism and
maintaining electrolyte and water balance (Takei & Loretz 2006). Many other
hormones also are involved in osmoregulation. For example, prolactin from the
anterior pituitary, along with cortisol, is important in freshwater adaptation.
Seawater adaptation involves cortisol, GH from the anterior pituitary, vasopressin
from the posterior pituitary, urotensins from the urophysis, atrial natriuretic peptide
from the heart, and probably others (Takei & Loretz 2006).
PANCREAS
Glucose metabolism is influenced by insulin , glucagon , and somatostatin from
cells within the pancreas. Insulin enhances the transport of glucose out of the
blood, promotes glucose uptake by liver and muscle cells, and stimulates the
incorporation of amino acids into tissue proteins. Glucagon and related glucagon-
like proteins seem to function in opposition to insulin, promoting the breakdown of
glycogen and lipids in the liver and increasing blood glucose levels. Somatostatin
also helps elevate blood glucose levels by promoting metabolism of glycogen and
lipids, and by inhibiting the release of insulin (Takei & Loretz 2006).
PINEAL GLAND
Melatonin , produced by the pineal gland (near the top of the brain) and the retina
of the eye, is secreted during the dark phase of daily light–dark cycles and helps
regulate f i sh responses to daily and annual cycles of daylight. This hormone infl
uences many physiological processes and behaviors through its role in the
maintenance of circadian activity cycles (see Chapter 23, Circadian rhythms), daily
changes in temperature preference, and changes in growth and coloration
associated with changes in photoperiod and temperature (Takei & Loretz 2006).
LECTURE NO.22
MALE REPRODUCTIVE

82
Gonads
� As in tetrapods, the sexes in fishes are usually separate (dioecious),
� with males having testes that produce sperm,
� and females having ovaries that produce eggs.
� “Fishes as a group exemplify almost every device known among sexually
reproducing animals;
� indeed, they display some variations which may be unique in the animal
kingdom” (Hoar 1969, p. 1).
� Only basic anatomy is treated here; other aspects of reproduction are discussed
in Chapters 9, 10, and 21.
Testes
� The testes are internal, longitudinal, and usually paired.
� They are suspended by lengthwise mesenteries known as mesorchia.
� The testes lie lateral to the gas bladder when one is present.
� Kidney tubules and ducts serve variously among different groups of fishes to
conduct sperm to the Chapter 4 Soft anatomy 53 outside
� Testes may constitute as much as 12% of body weight in some species at sexual
maturity, although this proportion is usually smaller.
Hagfishes and lampreys
� Hagfishes and lampreys have a single testis.
� Sperm is shed into the peritoneal cavity
� and then passes through paired genital pores into a urogenital sinus
� and out through a urogenital papilla.
Chondrichthyes
� Among Chondrichthyes, internal fertilization is universal,
� males using modified pelvic fins, termed claspers, to inseminate females.
� Sperm leave the testis through small coiled tubules, vasa efferentia,
� which are modifi ed mesonephric (kidney) tubules.
� Sperm pass through Leydig’s gland, whichconsists of small glandular tubules
derived from the kidney.
� Secretions of Leydig‟s gland are involved in spermatophore production.
� The sperm then go through a sperm duct,
� which is a modified mesonephric duct, and into a seminalvesicle,
� a temporary storage organ that is also secretory.

83
Actinopterygii
Among Actinopterygii, the situation is similar, but no true seminal vesicles or
sperm sacs are present.
� Marine catfishes (Ariidae), gobies (Gobiidae), and blennies (Blenniidae)
have secondarily derived structures that have also been called seminal vesicles,
� but these are glandular developments from the sperm ducts and are not
comparable to
structures with the same names in tetrapods.
� These vesicles provide secretions that are important in sperm transfer or other
breeding activities.
Lungfishes, sturgeons, and gars
� Lungfishes, sturgeons, and gars make varying use of kidney tubules and
mesonephric (Wolffian) ducts (Fig. 4.10).
� In the Bowfi n (Amia), vasa efferentia bypass the kidney
� and go to a Wolffi an duct. In Polypterus and the Teleostei,
� there is no connection between the kidney and gonads at maturity.
� The sperm duct is new and originates from the testes.
� Thus the sperm duct of more primitive fi shes such as the Chondrichthyes
� and Chondrostei is not homologous with that in the Teleostei.
� The tubular structure of the teleost testis has two basic types distinguished by
the distribution of spermatogonia,
� the sperm-producing cells.
teleosts
� In most teleosts, spermatogonia occur along the entire length of the tubules,
but in atherinomorphfishes the spermatogonia are confi ned to the distal end of the
tubules (Grier 1981).

84
FECUNDITY
� Fecundity, the number of eggs released by a female during a spawning bout
or breeding cycle, varies
� from one to two in some sharks
� to tens of millions in the Tarpon, Megalops atlanticus, and European Ling,
Molva molva, to 300 ×106 in the Giant Ocean Sunfish, Mola mola; seasonal
and lifetime fecundities can also be calculated.
� Mouth-brooders such as sea catfishes and some cichlids produce only about
100 eggs at a time, and live-bearers such as the Four-eyed
� Fish, Anableps, contain about a dozen embryos. The relationship between
egg number and body size is usually proportional to the mass of the female,
reflecting the volume of a female‟s body that can carry the eggs.
Fecundity
� egg size and number inversely related
� egg number directly related to female size (within species)
� Hence egg number generally increases in relation to the cube, fourth, or fifth
power of the length of the female. In addition to producing more eggs, larger
females of many species produce bigger, better eggs that result in higher larval
survival (e.g., in salmons, cod, haddock, Striped Bass, flounder) (Trippel 1995).
Fecundity
� fractional spawners produce eggs continuously,
spawn frequently
� batch spawners – single reproductive season
release all eggs in a short period
Frequency of reproduction
� semelparity - spawn and then die
- huge investment in egg production
� iteroparity - repeated reproduction
allows compensation for a “bad” year
more common in more unstable environments
may not spawn every year (sturgeon)

85
hagfish, lamprey: single gonads
no ducts; release gametes into body cavity
sharks: paired gonads
internal fertilization
sperm emitted through cloaca, along grooves in claspers
chimaeras, bony fishes: paired gonads
external and internal fertilization
sperm released through separate opening
most teleosts:
ova maintained in continuous sac from ovary to oviduct
exceptions: Salmonidae, Anguillidae, Galaxidae, non-teleosts
- these release eggs into body cavity when ripe

86
SPERMATOGENESIS
Spermatozoa are formed from the sperm mother cells or spermatogonia
through a series of cytological stages collectively referred to as
"spermatogenesis."
Spermatogonia---Spermatozoa or mature sperm
This process involves a proliferation of spermatogonia through repeated mitotic
divisions and growth to form primary spermatocytes; these then undergo reduction
division to form secondary spermatocytes;
the division of the secondary spermatocytes produces the spermatids which then
metamorphose into the motile and potentially functional gametes-spermatozoa,
spermia or sperm.
This process of spermatid metamorphosis is often called "spermiogenesis."
The process goes in this direction.
Spermatogonia--Primary spermatocyte--secondary spermatocyte--Spermatid-
-Sperm or Spermatozoa
Details of the cytological changes are similar in all vertebrates as described in
standard textbooks of histology and embryology.
Physiologists are interested in the factors both environmental and hormonal-which
trigger waves of spermatogenesis at different seasons and control the essential
steps of meiosis (division of primary to secondary spermatocytes) and the
metamorphosis of the spermatid with eventual release of mature sperm.
In some species -particularly the elasmobranchs and viviparous teleosts-sperm
produc tion involves the packaging of sperm into sperm balls or spermatophores
which are transferred to the female.
Spermatogenesis occurs within testicular units which may take the form of small
sacs, ampullae, lobules, or tubules;
In many groups of fishes these differ radically from the familiar seminiferous
tubules of the mammalian testis. seminiferous
In the cyclostome, spermatogenesis occurs within small bladders, follicles, or
ampullae. These are separated by a delicate connective tissue; a number of units
may be grouped together and bounded by somewhat thicker connective tissue to
form lobules (D odd et aZ., 1960; Walvig, 1963). connective
Spermatogenesis is almost synchronous throughout the many follicles and just
prior to spawning the follicles filled with mature sperm rupture to release their
contents into the body cavity.
Walvig (1963) summarizes the cytological details of spermatogenesis in Myxine.
In elasmobranchs, spermatogenesis occurs within a mass of ampullae arranged in a
manner which seems to be unique among the vertebrates. The testis of the basking
shark, Cetorhinus maximus, carefully described by L. H. Matthews (1950), is
divided by connective tissue trabeculae into many lobules each of which

87
corresponds to the entire testis of the dogfish, Scylliorhinus canicula, as described
by Fratini (1953) and Mel linger (1965). The structure of the dogfish testis is
shown diagram matically in Fig. 4. The spermatogenetic units, usu ally called
"ampullae," are proliferated from a mesoventral area of the testis referred to as the
"tubulogenic zone." Within this zone, nests of cells-somewhat like primary
ovarian follicles-arise and proliferate to form small tubules or ampullae which
gradually shift toward the dorsal side of the organ while spermatogenesis occurs
within them. By the time the ampullae reach the dorsal surface of the testis, the
sperm (a constant number in each am pulla : Stanley, 1962; Mellinger, 1965) are
ready for discharge into the efferent ducts which emerge from the testis at this
point. At this stage, the Sertoli cells surround the ampullae and are clearly
associated with packets of sperm. According to L. H. Matthews (1950), the
ampullae shrink after sperm are discharged into these collecting tubules and the
Sertoli cells are resorbed. It is of interest that all of the gonocytes within any one
ampulla are in the same stage of spermatogenesis and that within the testis,
distinct zones are evident from ventral to dorsal surface with all the tubules of a
particular zone in a similar stage of development. Thus, in studies of the pituitary
regulation of spermatogenesis, Dodd and his colleagues (1960) were readily able
to spot a distinct zone of de generation in the primary spermatocytes when it
appeared following hypophysect omy. The cytology of the elasmobr anch testis,
including spermatogenesis, the development of the Sertoli cells, and the formation
of spermatophores, has been detailed by L. H. Matthews (1950) and Fratini (1953).
There are now good descriptions of the testicular histology of several species of
teleosts. Among the early papers, the following are particu larly helpful: C. L.
Turner's description (1 919 ) of the spermary of the perch, Craig-Ben nett's account
(1 931 ) of the stickleback, S. A. Matthews'
report (1 938 ) on Fundulus, and Cooper's study (1 952 ) of the crappies. Many
other investigations are cited in the bibliographies of these papers and in the
reviews by Hoar (1 957 ) and Dodd (1 960a ). More recent descriptions are
available for the minnow Couesius (A hsan, 1966a,b ), the rockfish Sebastodes (M
oser, 1967a ), the sea perch Cymatogaster (W iebe, 1968b ), and the guppy Poecilia
(P andey, 1969a ,c ). Testes of different species vary in complexity; the brief desc
ription which follows is a gener alized one. The main sperm duct (v as defe rens )
arises from the posterior meso dorsal surface of the elongated testis and leads to
the urin ogenital papilla. It may be traced anteriorly for a variable distance in a
connective tissue groove of the testis along with the spermatic blood vessels and
nerves. In many teleosts, the paired testes fuse posteriorly and the vasa deferentia
are combined into a single sperm duct. Within the body of the testis, the main
sperm ducts give rise to smaller ducts (v asa efferentia ) which pene trate ventrally
and laterally to form a drainage system of variable com plexity. In some species

88
these tubules are extremely short (p oeciliids, for example ), while in others they
form an extensive system of seminiferous tubules which can be followed almost to
the periphery of the organ (Fundulus, the rockfish es, and the cottids ). Testes of
the poeciliid type are sometimes referred to as "acinar" (F ig. 5) while those with
the extensive duct systems are called "tubular." This difference is one of degree
rather than kind.
It is to be noted that the seminif erous tubules of the teleost-in contrast to those of
the higher vertebrates-lack a permanent germinal epitheli um. 'Whether the testis
is acinar or tubular, nests of spermatogonia proliferate from the resting germ cells
near the margin of the organ. In the acinar typ e, these nests of cells or cysts
undergo the various stages of maturation as they are displaced toward the sperm
ducts into which they eventually discharge their contents (F ig. 5). In the tubular
testis, the resting germ cells are particularly ev ident and packed together at the
blind ends of the tubules near the periphery, but many of them migrate or are
displaced along the walls of the tubules. In active spermatogenesis, nests of
spermatogonia proliferate both from the ends of the tubules and from the resting
germ cells along their walls. Thus, at the end of spermio genesis, the seminiferous
tubules are packed with sperm as the masses of gametes from a multitude of
matured cysts combine within the tubules. During maturation all of the cells within
one of the cysts are in approxi mately the same stag e of development; the degree
of synchrony among the many cysts varies in different species.

89
LECTURE NO. 23
FEMALE REPRODUCTIVE
Ovaries
The ovaries are internal,
� usually longitudinal,
� and primitively paired
� but are often variously fused and shortened.
� Sometimes only one ovary is present in adults, as in some needlefishes
(Belonidae).
� The number or relative lengths of the ovaries are a useful taxonomic character
in some fishes, such as the needlefishes.
� The ovaries are suspended by a pair of lengthwise mesenteries, the mesovaria.
� The ovariesare typically ventral to the gas bladder.
� Kidney tubules and ducts are not used to transport eggs.
� Ovary mass can be as high as 70% of body weight and tends to increase with
body size of individual females.
hagfishes and lampreys
� Ovaries of hagfi shes and lampreys have the same basic structure as do the male
testes.
� There is a single ovary,
� and the eggs are shed into the body cavity
� and then pass through paired genital pores
� and out through a urogenital papilla.
Chondrichthyes
In Chondrichthyes, the ovarian capsule is not continuous with the oviduct so eggs
are shed into the body cavity, the gymnovarian condition.
� The eggs enter the funnel of the oviduct,
� which is a Müllerian duct, not a modified mesonephric duct;
� it develops as a posterior continuation of the ovarian tunic.
� The anterior part of the oviduct is specialized to form a nidamental or shell
gland where fertilization takes place.
� The nidamental gland secretes a membrane around the fertilized egg.

90
� In oviparous (egg-laying) taxa, the membrane is horny, composed of keratin.
� The nidamental gland may function as a seminal receptacle
where sperm are nourished before fertilization.
� In viviparous (live-bearing) species, the posterior part of the oviduct is modifi
ed to form a uterus,
� which houses the developingembryo.
osteichthyan fishes
� In osteichthyan fi shes, the primitive gymnovarian condition is found in lungfi
shes, sturgeons, and the Bowfi n. Ingars and most teleosts, the lumen of the hollow
ovary is continuous with the oviduct, termed the cystovarian condition.
� In trouts and salmons (Salmonoidei) and some other teleosts,
� the oviducts have been secondarily lost in wholeor in part,
� so the eggs are shed into the peritoneal cavity and reach the outside through
pores.

91
LECTURE NO. 24. EYE STRUCTURE
� Structure very much like other vertebrates
� Cornea
� Sclera
� Lens
� Conjunctiva
� Iris
� Choroid layer
� Retina
� Vitreous & aqueous chambers
Visual Cells of Fish Eyes
� Rods
� Dominate in deep dwelling fish
� Cones
� Sometimes long & short
� Double cones
� Maximum absorbance range of fish eyes
� Some down to 360nm (UV)
� Some up to 625 nm (red)
Problems Associated with Aquatic Vision
� Less light enters water
� Water disturbances change angle of incidence
� Some species rely on seeing out of the water to locate prey
Protection for Eyes
� Eyelids are well developed in some elasmobranchs
� Eyes can not bulge
� Cornea is often made of four layers
� Multicellular epithelium
� Collagenous stroma
� Descemet�s membrane
� Endothelium
Differences Among Fish Eyes
� Placement

92
� Sides of head
� Most common
� Wide lateral fields of vision
� No binocular vision
� Eyes set forward
� Eyes set upward
� Extra eye monitors area below
� Stalked eyes
� A few fish have eyes capable of terrestrial and/or aquatic viewing
� Some fish have vestigial eyes or lack eyes
Importance of Eyes
� Some fish are very visual
� In many fish, vision is not the primary sense
� Some fish are blind

93
LECTURE NO. 25. HEARING IN FISH
Ear
In almost all fishes, there is no external and middle ears.
Only an internal ear is present which is called membranous labyrinth.
It is a delicate membranous sac found embedded in the cartilaginous olfactory
capsule, one on either postero-lateral side of cranium.
The main body or vestabule of membranous labyrinth is laterally compressed and
made of a dorsal utriculus from which projects a ventral and posterior lobe, the
sacculus.
A posterior outgrowth of sacculus is called lagena cochleae.
An anterior outgrowth of utriculus is known as recessus utriculi.
Arising from vestibule are three tubes, known as the semicircular canals.
They are at right angles to one another and one end of each bears a swelling or
ampulla.
Endolymph
The cavity of membranous labyrinth contains a fluid, the endolymph, in which
float minute calcareous particles known as the otoliths.
From the endolymphatic cavity of sacculus arises a slender tube called the ductus
endolymphaticus.
It opens to outside on the top of cranium by its aperture lying in the parietal fossa.
Perilymphatic space
The space between auditory capsule and membranous labyrinth is the
perilymphatic space.
Perilymph
The fluid present in the perilymphatic space is known as the perilymph.
The large external opening of perilymphatic space, called fenestra also lies behind
the small aperture of endolymphatic duct on the top of cranium.
Auditory nerve
Membranous labyrinth is innervated by the auditory nerve.
Group of receptors or sensory cells bearing stiff hairs are confined to definite spots,
those of utriculus and sacculus called maculae and those of ampullae of
semicircular canals called cristae.
Physiology of ear
Ear of fishes are also called stato-acoustic organs because of their two important
functions, as follows.

94
a) Static function
Internal ears are primarily concerned with balance or equilibrium. Movements of
endolymph and otoliths stimulates sensory nerve endlings in ampullae and
vestibule, thus informing the animal about its position in water. The animal can
detect changes in speed, direction and orientation and adjust accordingly.
(b) Accoustic function
Sacculus and lagena perhaps recieve auditory stimuli forming organs of hearing
Gills

Fisheries and Aquaculture by Abdul Hameed Korai ( Tehsildar )

Fisheries and Aquaculture by Abdul Hameed Korai ( Tehsildar )

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