Fish are the gill-bearing aquatic craniate animals that lack limbs with digits. They form a sister group to the tunicates, together forming the olfactores. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups.

2. PiscesPisces
• L. piscis, fish
• Exclusively aquatic, cold-blooded, oviparous and
ovoviviparous vertebrates
• Paired and unpaired fins and supported by dermal fin rays
• Skin usually moist and scaly
• Exoskeleton of dermal scales, denticles or bony plates
• Endoskeleton cartilaginous or bony
• Respiration by gills
• L. piscis, fish
• Exclusively aquatic, cold-blooded, oviparous and
ovoviviparous vertebrates
• Paired and unpaired fins and supported by dermal fin rays
• Skin usually moist and scaly
• Exoskeleton of dermal scales, denticles or bony plates
• Endoskeleton cartilaginous or bony
• Respiration by gills

3. Types of fins
1. Unpaired median fins
2. Paired lateral fins
Uses of fins:
 Caudal fin or tails are used for swimming
 Others fins are used as steering and rudders
 When the body is at rest, the paired lateral fins serve to maintain
equiibrium
 Lungfishes use them legs in walking
 The flying fish use their large and extended pectoral fins for glding
 Pelvic fins of Chondrichthyes male modified into claspers
 In remoras, anterior dorsal fin forms an adhesive disc or sucker on head

4. Types of Caudal fin

6. Types of scales
Scales are external coverings that grows out of an
animal’s skin to provide protection
Two types-epidermal and dermal
Dermal scales are small, thin, cornified, calcareous
and bony plates which fit closely together or
overlap each other on the body of fish

7. Cosmoid Scales:
Do not found in living fishes
Found in ostracoderms, placoderms and extinct
sarcopterygians (lobe finned fishes and lung fishes)
4 distinct layers-
Upper layer is thin enamel-like ganoine
Second layer is thick, dentine like cosmine
Third layer is spongy bone
Lowest layer is compact bone
This scales grow along with the fish

9. Placoid scales:
 Found in elasmobranch fishes-shark, skate and rays
 Each placoid scale consists of a backwardly directed spine
arising from a rounded or rhomboidal basal plate embedded in
dermis
 Spine is made of enamel-like and basal plate of dentine-like
bony material
 A pulp cavity inside spine opens through basal plate
 This scale donot grow with the fish. When the shark gets longer,
new scales grow to fill the gaps between the scales

11. Ganoid scales:
 Found in the chondrosteans such as gars, bichirs and reed fishes
(Polypterus, Acipencer, Leipidosteus)
 They are thick, flat and diamond-shaped scales
 They closely fitted side by side like tiles or pieces of jigjug puzzles,
instead of overlap each other.
 They provide a bony armour to the fish
 In Polypterus, This scales composed of 3 layers-
 Upper layer is enamel like ganoine
 Middle layer is dentine-like cosmine
 Inner layer is bony isopedine
 In Leipidosteus, two layers-
 Upper layer is enamel like ganoine
 Inner layer is bony isopedine

13. Cycloid scales:
 These type of scales are found in lung fishes, some
holosteans (Amia), and the most of the teleostean fishes
which have soft fin-rays such as carp, Hilsha, salmon etc.
 The word cycloid comes from the Greek word cyclo
meaning circle
 These scale are roughly circular in outline with smooth
outer edge
 Cycloid scales increase in size with the increasing the size
of that fish
 They are marked with several concentric lines of growth
which are called circuli, used for the determining the age of
the fish

14. During the cooler months of the year the scale grows more slowly and the
circuli are closer together leaving a band called an annulus. By counting the
annuli it is possible estimate the age of the fish.

15. Ctenoid scale:
 Found in those fishes with spiny fin rays such as perch, bass etc.
 Their outer edge (exposed part) have numerous small comb-like
teeth or spines.
 The word ctenoid comes from the Greek word cteno meaning comb
and refers to the comb-like ctenii on the margin of the scale
 Cycloid and ctenoid scale overlap each other which gives the fish
greater flexibility than those species with ganoid and cosmoid scale
 Some species of flatfishes such as soles, flounders bear two types,
ctenoid scale dorsally and cycloid scale ventrally

17. Functions of scales:
 Form a protective covering of exoskeleton on the body
 The age of the fish is also determined from the growth rings of the
scales
Modifications of scale:
 In eels, scales are minute and deeply embedded in dermis
 In some fishes (chimaeras), they become localized
 In globe fish (Tetradon) and porcupine fishes (Diodon), they
develop it into large protective spines making it difficult to be
swallowed.
 Shark teeth are modified large placoid scale
 Sting (barb) of a sting ray is a modified large placoid scale
 The teeth on the elongated rostrum of sawfish (Pristis) are formed
by placoid scales

19. PlacodermiPlacodermi
• Several early primitive jawed fishes
• Bony head shield movably articulated with
trunk shield
e.g. Dinichthyes
• Several early primitive jawed fishes
• Bony head shield movably articulated with
trunk shield
e.g. Dinichthyes

20. • Gr. Chondros, cartilage; ichthys, fish
• Mostly marine
• Cartilaginous endoskeleton
• Skin with placoid scales
• Mouth ventral and teeth are modified placoid scales
• Gill slits not covered by operculum
• Pelvic claspers in male
• Sexual reproduction with internal fertilization
e.g. sharks, rays, skates
• Gr. Chondros, cartilage; ichthys, fish
• Mostly marine
• Cartilaginous endoskeleton
• Skin with placoid scales
• Mouth ventral and teeth are modified placoid scales
• Gill slits not covered by operculum
• Pelvic claspers in male
• Sexual reproduction with internal fertilization
e.g. sharks, rays, skates
Class: ChondrichthyesClass: Chondrichthyes

21. Classification
Subclass Elasmobranchii
 Cylindrical or flattened body
 5-7 pairs of gill slits
 An upper jaw not fused to the cranium
 Have placoid scales
Superorder Selachii (Gr., selachos, a shark)
 Multiple gill slits on either side protected by individual skin flaps
 A spiracle behind each eye
 Cloaca present

22. Order 1. Squaliformes or Pleurotremata (Gr., pleuro-side+trema-
opening)
 Body typically spindle-shaped.
 Gill-slits lateral, 5-7 pairs
 Spiracles small
 Pectoral fins moderate, constricted at base
 Tail heterocercal
e.g. Dogfish shark (Scoliodon)

23. Order 2. Rajiformes or Hypotremata (Gr., hypo-below+ trema-
opening)
 Body depressed, flattened dorso-ventrally
 Gill-slits ventral, 5 pairs
 Spiracles large, highly functional
 Pectoral fins enlarged, fused to sides of head and body
e.g. Skate (Raja), Electric ray (Torpedo), Sawfish (Pristis)

24. Subclass 2. Holocephali (Gr., holos-entire+ kephale-
head)
 Single gill opening on either side covered by a fleshy operculum
 Upper jaw fused to the cranium
 No spiracles, cloaca and scales
 Jaws with hard, flat plates instead of tooth
 Single nasal opening
e.g. Rat fishes or chimaeras

25. Shark
 About 300 living species
 Most of them are marine with a few exceptions such as the bull shark and the river shark which
can live both in seawater and freshwater
 They are distinguished by their muscular strength, agility of movements, well-developed sense
organs and powerful jaws
 Largest living vertebrates, after whales, reaching up to 12 m in length
 A mature whale shark (Rhincodon typicus) may reach 15-17 m in length

26. No anal fin
Body flattened, ray-like
and mouth terminal
Snout elongated,
saw-like
Body not flat, ray-like and
mouth ventral
Snout short , not
saw-like
Squatiniformes
Triassic
Pristiophoriformes
Jurassic
Squaliformes
Jurassic
Hexanchiformes
Permian
Anal fin
6-7 gill slits,
1 dorsal fin
5 gill slits, 2
dorsal fins
No fin
spines
Dorsal fin
spines
Mouth behind
front of eyes
Mouth in
front of eyes
Nictitating eyelids,
spiral intestinal valve
No Nictitating eyelids,
ring intestinal valve Lamniformes
Jurassic
Orectolobiformes
Jurassic
Heterodontiformes
Triassic
Carcharhiniformes
Jurassic

27. Orders of Shark
Squatiniformes - Angel sharks
Pristiophoriformes - Sawsharks
Squaliformes - Dogfish shark, Bramble shark
Hexanchiformes: Cow sharks and Frilled sharks
Carcharhiniformes – Tiger shark, Bull sharks, Hammerhead shark,
Milk shark
Lamniformes-- White shark, Basking shark, Great white shark
Orectolobiformes—Carpet shark, Whale sharks, Zebra shark
Heterodontiformes: Bullhead or Horn sharks.

28. Angel shark
Dogfish shark

29. Sharks

30. More Sharks

31. External features
 Body is divisible into three regions- head, trunk and tail
 Head is dorso-ventrally flattened and produced in front into a
pointed rostrum or snout.
 Trunk is almost oval and gradually tapers to the tail
 Tail forming the posterior half of the body is slightly bent
upwards
 Body surface is rough due to backwardly projecting spines of
placoid scales

32. Body Structures of a Shark

33. Fins:
 Fins are flap-like outgrowths of bodywall and internally supported by
cartilaginous rods and horny finrays.
Median fin- 1st
and 2nd
dorsal, anal, caudal fin
Lateral fin- Pelvic fin, Pectoral fin
Eyes
Body apertures
Mouth:
 Mouth is a crescentic opening lying ventrally on head near its anterior
end
 Each jaw bears one or two rows of sharply pointed and backwardly
directed teeth adapted for holding and tearing.
 Teeth are polyphyodont
Nares or nostrils: Olfactory organs

34. External gill slits:
Cloacal aperture:
Abdominal pore:
Caudal pits:
 At the base of caudal fin, one
ventral and dorsal caudal pits
Lateral line
Ampullae of Lorenzini

35. Feeding
 Most sharks are carnivorous
 Sharks such as Whale shark (Rhincodon), Basking shark
(Cetorhinus maximus) are filter feeder and have reduced or
nonfunctional teeth.
 Sharks those eat mollusks and crustaceans have dense flattened
teeth for crushing
 Those eat larger preys have pointed lower teeth for gripping and
triangular upper teeth with serrated edges for cutting

36. Digestive system
Alimentary canal:
 Mouth
 Buccal cavity
 Pharynx
 Oesophagus
 Stomach
 Intestine
Glands of alimentary canal:
 Liver
 Pancreas
 Rectal gland
 Spleen

37. Digestion
Food is swallowed without mastication
No digestion occurs in buccal cavity which lacks salivary
glands.
The gastric juice in stomach contains pepsin and
hydrochloric acid
Proteins into syntonin, proteoses and peptones, but cannot
digest chitin
Liver secretes bile which makes the semidigested food
alkaline in intestine
Pancreas secretes trypsinogen, amylopsin and lipase for
digestion of proteins, starches and fats
Spiral valve in intestine serves to delay the passage of
food and offers a large surface for absorption of the products
of digestion.

38. Male reproductive organ
 Testes-attached to the bodywall by
a peritoneum fold called
mesorchium
 Fine tubules-Vasa efferentia
 Vas deferens or Wolffian duct
 Seminal vesicle- storage of
spermatozoa
 Opens separately into urogenital
sinus

39. Female reproductive
organ
A pair of ovaries
Mesovarium
Oviducts
Oviducal funnel
Shell gland
Uterus

40. Reproduction and development

41.  Sharks may be oviparous, ovoviviparous and
viviparous
 Oviparous sharks deposit their eggs in the ocean
that will hatch later
 Parents does not guard the eggs
 Tough leathery membrane covers shark eggs which
are called mermaid’s purse
e.g. Cat shark, Horn shark, Leopard shark

42. Viviparous shark:
 These give birth to live young
 The eggs hatch inside the female’s body
and get nourishment from the mother
through the placenta (via an umbilical
cord which is connected to the pup
between the pectoral fins)
e.g. Bull shark, Hammerhead shark, Mako
shark

43. Ovoviviparous shark:
 Most sharks are ovoviviparous
 The eggs hatch inside the female body but they don't nourish
through the placenta
 The pups are nourished from the egg’s yolk and fluids secreted
by glands in the walls of the oviduct
 The pups have cannibalistic behaviour
e.g. Great white shark, Saw shark, Tiger shark

44. Senses
• Olfactory organs can detect chemicals
diluted 1/10 billionth their original
concentration
• Lateral line senses low frequency
vibrations of prey over large distances
• Excellent vision, even in dim water,
used at close range
• At close range, sharks are guided to
prey by electric fields surrounding all
animals
• Buoyancy

45. Shark Attacks
• Only 32 species ( of 350) have been documented
to attack humans with another 36 considered
potentially dangerous; these typically are the larger
size sharks; 80 % of sharks are harmless
• Great white, tiger, and bull sharks are the more
aggressive species
• 50-75 attacks occur each year, with 8-12 fatalities;
in contrast 30-100 million sharks are killed every
year
• Attacks usually occur by sandbars, steep drop offs,
or by river inlets and are associated with mistaken
identity,territorial behavior, or feeding behavior

46. Economic importance of Shark

47. Skates and Rays
Make up half of all species of Elasmobranchii
Order Rajiformes—skates
Order of Rays
 Order Myliobatiformes- Dasyatis (Stingrays), Mobula (Devil rays),
Himantura (Haushpata) etc.
 Order Torpediniformes- Torpedo (Electric rays)
Order Pristiformes- Pristis pristis ( Common sawfish)

49. Form and Function
• Specialized for benthic life
• Flattened dorso-ventrally; enlarged pectoral fins are used as swimming
wings
• Water used in respiration enters large spiracles in head
• Teeth adapted to act as rollers to crush invertebrates and sometimes
small fish
• Stingrays have whip-like tail with spines and venom glands
• Electric rays have electric organs on sides of head
• Skates look like kites with a sharp tail.

52. Economic importance of ray
Flesh of ray is delicious food.
The oil produced from liver of ray is good food
They are also used for producing fish meal,
fish flour for the poultry feeds
The fins of Blue-spotted string ray are sun-
dried and exported to other countries for used
in much relished soups.

53. Class Osteichthyes
–Endoskeleton chiefly of bone except sturgeons
–3 types of scales
–Fin are supported by bony fin rays
–Lung or swim bladder
–Bony operculum
–Jaws usually with teeth. Cloaca lacking

54. SubClass Sarcopterygii
 Greek, sarcos-fleshy and pterygium-fin
 Only 4 species alive today; 3 lungfishes
and 1 coelacanth
 Popularly called as lobe-finned or air-
breathing fish
 Paired fins are lobed with a fleshy central
axis covered by scales; sometimes used
as leg
 2 dorsal fins, heterocercal caudal tail;
 South American and African lungfishes
can survive out of water or long periods of
time
 Divided into orders-Crossopterygii and
Dipnoi
e.g. Latimeria, Protopterus

55. Order Crossopterygii
 Greek, crossoi-a fringe, pteryx-fin
 Paired fins lobate. Caudal fin 3-lobed
 Spiracles present
 Air bladder vestigial
e.g. primitive fleshy-finned extinct fishes. Single
living genus, Latimeria

56. Order Dipnoi
 Greek, di-double and pnoe-breathing
 Median fins continuous to form diphycercal tail
 Air bladder single or paired, lung-like
e.g. lung fishes. Only 3 living genera. Protopterus

57. Subclass Actinopterygii
Greek, actis-ray and pteryx-fin
Popularly called ray-finned fishes
Paired fins thin, broad, without fleshy basal lobes and
supported by dermal finrays.
Caudal fin without epichordal lobe
Divided into 3 superorders: Chondrostei, Holostei and
Teleostei

59. Superorder 1. Chondrostei
 Primitive ray-finned fish or cartilaginous ganoids
 Scales usually ganoid
 Mouth opening large
Order 1. Polypteriformes
 Rhomboid ganoid scales and lobed pectoral fins
 Ossified skeleton
e,.g. Polypterus (Bichir)
Order 2. Acipenseriformes
 Scaleless except for bony (ganoid) scutes
 Skeleton largely cartilaginous
e.g. Acipenser (Sturgeon), Polyodon (Paddle fish)

60. Superorder 2. Holostei
Greek, holos-entire andosteon- bone
Mouth opening small
Ganoid or cycloid scales
Intermediate ray-finned fish, transitional between Chondrostei and Teleostei
Order 1. Amiiformes
Thin, overlapping cycloid scales
Long dorsal fin
Snout normal, rounded
e.g. Amia (bowfin)
Order 2. Semionotiformes
Ganoid scales
Snout and body elongated
e.g. Lepidosteus (garpike)

62. Superorder 3. Teleostei
 Greek, Teleos-complete and osteon-bone
 Mouth opening terminal, small
 Scales cycloid, ctenoid or absent
 Tail fin mostly homocercal
 A hydrostatic swim bladder usually present
 Advanced or modern ray-finned fishes
e.g. Anabas testudineus, Polynemus paradiseus

63. Order Osteoglossiformes

64. Order Elopiformes
Order Anguilliformes
Order Clupeiformes

65. Order Cypriniformes
Order Gonorhynchiformes
Order Channiformes

66. Order Characiformes
Order Siluriformes
Order Syngnathiformes

67. Order Cyprinodontiformes
Order Synbranchiformes
Order Perciformes

68. Order Scorpaeniformes
Order Beloniformes
Order Pleuronectiformes

69. Order Mastacembeliformes
Order Tetraodontiformes
Order Scopeliformes

70. Order Lophiiformes
Order Echeneiformes

71. Specialized auditory structure
One of the most notable
complex system in teleost fish
especially in the order
cypriniformes
It is a mechanical device
improving audition, consisting of a
double chain of ossicles joining to
the air bladder to the inner ear
Comprises four bony elements-
claustra, scaphia, intercalarium
and tripus
Weberian apparatus

72. Accessory Respiratory Organ
 Skin or integument- Common eel, Mudskippers
 Bucco-pharyngeal epithelium
 Gut epithelium
 Pelvic fin-American Lung fish
 Pharyngeal diverticula- Amphipnous, Channa
 Branchial diverticula-
 Heteropneustes as long tubular air sac
 Anabas as labyrinthine organ
 Clarias as tree-like arborescent organ
 Air bladder

74. Parental care in fish
 Nest building- Stickleback, Bowfin, African lung fish, American
lung fish
 Coiling round eggs
 Attachment to body
 Integumentary cups
 Shelter in mouth
 Brood pouches
 Mermaid’s purses
 Viviparity

77. Swim Bladder
• Fish are slightly heavier than water
• A shark has a very fatty liver that makes it a little buoyant; must also keep
swimming to move it forward and angle itself up
• Bottom dwelling fishes also lack swim bladder
• Fish can control depth by adjusting volume of gas in swim bladder
• Gas gland removes or adds gases from blood to remove or add gas to
bladder
• Some fish gulp air to fill swim bladder
Function:
 Act as accessory respiratory organ
 Act as hydrostatic organ
 Produce sound
 Help in audition

79. Teeth
 The size of the teeth of fish depends on the feeding habits of fish
 Some fishes have sharp-edged cutting teeth called incisors located in
the forward part of mouth
 Some possess some conical teeth known as canines
 Some have molariform teeth that are well-adapted for crunching food
 Some have volariform teeth that are slender and form velvety bands
 Fishes like carp, minnows and suckers have teeth in their throat
called pharyngeal teeth.

81. Economic importance of fish