physiology of fishes

1. PHYSIOLOGY OF
FISHES
BY SAFIAAFRIDI

2. LOCOMOTION
 Fishes move through water their fins and body
wall to push against the incompressible
surrounding water.
 Muscles bundles of fishes are arranged in zig
zag manner thats why contraction of each
muscle bundle can effect relatively large portion
of body wall.
 Fast swimming fishes are suplemented with a
vertical caudal fin that is tall and forked (e.g in
tuna).

3. NUTRITION AND DIGESTION
 Most modern fishes are predators, some
feeds on invertebrates, many feeds on
vertebrates.
 Fishes usually swallow whole prey.
 Fish ingest food through the mouth and
break it down in the oesophagus.
 In the stomach, food is further digested and,
in many fish, processed in finger-shaped
pouches called pyloric caeca, which secrete
digestive enzymes and absorb nutrients.

4. NUTRITION AND DIGESTION
 Organs such as the liver and pancreas add
enzymes and various chemicals as the food
moves through the digestive tract.
 The small intestine is the part of the digestive
tract following the stomach and followed by
the large intestine, and is where much of
the digestion and absorption of food takes
place. In fish, the divisions of the small intestine
are not clear, and the
terms anterior or proximal intestine may be used
instead of duodenum.

5. NUTRITION AND DIGESTION
 The large intestine is the last part of
the digestive system normally found in
vertebrate animals. Its function is to absorb
water from the remaining indigestible food
matter, and then to pass useless waste
material from the body.
 As with many aquatic animals, most fish release
their nitrogenous wastes as ammonia. Some of
the wastes diffuse through the gills. Blood
wastes are filtered by the kidneys.

6. CIRCULATION
 Fish have a closed-loop circulatory system.
 In most fish, the heart consists of four parts,
including two chambers and an entrance and
exit.
 The first part is the sinus venosus, a thin-
walled sac that collects blood from the
fish's veins before allowing it to flow to the
second part, the atrium, which is a large
muscular chamber.

7. CIRCULATION
 The atrium serves as a one-way
antechamber, sends blood to the third
part, ventricle. The ventricle is another thick-
walled, muscular chamber and it pumps the
blood, first to the fourth part, bulbus
arteriosus, a large tube, and then out of the
heart. The bulbus arteriosus connects to
the aorta, through which blood flows to
the gills for oxygenation

8. CIRCULATION
 In fish, the system has only one circuit, with
the blood being pumped through the
capillaries of the gills and on to the capillaries
of the body tissues. This is known as single
cycle circulation.

9. RESPIRATION
 Most fish exchange gases using gills on
either side of the pharynx (throat). Gills are
tissues which consist of threadlike structures
called filaments. These filaments have many
functions and "are involved in ion and water
transfer as well as oxygen, carbon dioxide,
acid and ammonia exchange

10. RESPIRATION
 Fishes lives in environment that contain less
than 2.5% oxygen present in the air.
 To maintain adequate amount of oxygen in their
bloodstream they must pass large amount of
water across their gill surface and extract small
amount of oxygen present in the water.
 Some elasmobranch and bony fishes maintain
water flow by holding their mouth open wahile
swimming, this method is called ram vantilation.
 Other move water over their gills.

11. RESPIRATION
 The gills of vertebrates typically develop in the walls
of the pharynx, along a series of gill slits opening to
the exterior.
 Most species employ a countercurrent
exchange system to enhance the diffusion of
substances in and out of the gill, with blood and water
flowing in opposite directions to each other, which
increases the efficiency of oxygen-uptake from the
water.
 Fresh oxygenated water taken in through the mouth
is uninterruptedly "pumped" through the gills in one
direction, while the blood in the lamellae flows in the
opposite direction, creating the countercurrent blood
and water flow, on which the fish's survival depends.

12. BUOYANCY
 The body of a fish is denser than water, so
fish must compensate for the difference or
they will sink.
 Many bony fishes have an internal organ
called a swim bladder, or gas bladder, that
adjusts their buoyancy through manipulation
of gases.
 Another adaptation is the reduction of heavy
tissues in fishes.

13. BUOYANCY
 Unlike bony fish, sharks do not have gas-filled
swim bladders for buoyancy. Instead, sharks
rely on a large liver filled with oil that
contains squalene, and their cartilage, which is
about half the normal density of bone.
 Their liver constitutes up to 30% of their total
body mass.
 The liver's effectiveness is limited, so sharks
employ dynamic lift to maintain depth when not
swimming.

14. NERVOUS AND SENSORY FUNCTION
 Most fish possess highly developed sense
organs.
 Many fish also have chemoreceptors that are
responsible for extraordinary senses of taste
and smell.
 Most fish have sensitive receptors that form
the lateral line system, which detects gentle
currents and vibrations, and senses the motion
of nearby fish and prey.
 Sharks can sense frequencies in the range of
25 to 50 Hz through their lateral line

15. NERVOUS AND SENSORY FUNCTION
 Vision
 Fish eyes are similar to those
of terrestrial vertebrates like birds and mammals, but
have a more spherical lens. Their retinas generally
have both rod cells and cone
cells (for scotopic and photopic vision), and most
species have colour vision.
 Some fish can see ultraviolet and some can
see polarized light. Amongst jawless fish,
the lamprey has well-developed eyes, while
the hagfish has only primitive eyespots.
 Fish vision shows adaptation to their visual
environment, for example deep sea fishes have eyes
suited to the dark environment.

16. NERVOUS AND SENSORY FUNCTION
 Hearing
 Fish can sense sound through their lateral
lines and their otoliths (ears). Some fishes, such
as some species of carp and herring, hear
through their swim bladders, which function
rather like a hearing aid.
 Hearing is well-developed in carp, which have
the Weberian organ, three specialized vertebral
processes that transfer vibrations in the swim
bladder to the inner ear.

17. NERVOUS AND SENSORY FUNCTION
 Chemoreception
 Sharks have keen olfactory senses, located
in the short duct (which is not fused, unlike
bony fish) between the anterior and posterior
nasal openings, with some species able to
detect as little as one part per million of blood
in seawater.

18. NERVOUS AND SENSORY FUNCTION
 Electroreception
 Some fish, such as catfish and sharks, have
organs that detect weak electric currents on the
order of millivolt.
 Other fish, like the South American electric
fishes Gymnotiformes, can produce weak
electric currents, which they use in navigation
and social communication.
 Electric fish are able to produce electric fields by
modified muscles in their body.

19. NERVOUS AND SENSORY FUNCTION
 Electroreception
 In sharks, the ampullae of Lorenzini are
electroreceptor organs
 hey number in the hundreds to thousands.
Sharks use the ampullae of Lorenzini to
detect the electromagnetic fields that all
living things produce.

20. NERVOUS AND SENSORY FUNCTION
 Electroreception
 The shark has the greatest electrical
sensitivity of any animal.
 Sharks find prey hidden in sand by detecting
the electric fields they produce. Ocean
currents moving in the magnetic field of the
Earth also generate electric fields that sharks
can use for orientation and possibly
navigation

21. REPRODUCTION
 Over 97% of all known fish are oviparous, that is, the
eggs develop outside the mother's body. Examples of
oviparous fish include salmon, goldfish, cichlids, tuna,
and eels.
 In the majority of these species, fertilisation takes place
outside the mother's body, with the male and female fish
shedding their gametes into the surrounding water.
 However, a few oviparous fish practice internal
fertilisation, with the male using some sort of intromittent
organ to deliver sperm into the genital opening of the
female, most notably the oviparous sharks,
 such as the horn shark, and oviparous rays, such
as skates. In these cases, the male is equipped with a
pair of modified pelvic fins known as claspers.

22. REPRODUCTION
 In ovoviviparous fish the eggs develop inside
the mother's body after internal fertilisation
but receive little or no nourishment directly
from the mother, depending instead on
the yolk. Each embryo develops in its own
egg. Familiar examples of ovoviviparous fish
include guppies, angel sharks,
and coelacanths

23. REPRODUCTION
 Some species of fish are viviparous. In such
species the mother retains the eggs and
nourishes the embryos.
 Typically, viviparous fish have a structure
analogous to the placenta seen
in mammals connecting the mother's blood
supply with that of the embryo.
 Examples of viviparous fish include the surf-
perches, splitfins, and lemon shark.

24. OSMOREGULATION
 Two major types of osmoregulation are
osmoconformers and osmoregulators.
 Osmoconformers match their body osmolarity
to their environment actively or passively. Most
marine invertebrates are osmoconformers,
although their ionic composition may be different
from that of seawater.
 Osmoregulators actively control salt
concentrations despite the salt concentrations in
the environment. An example is freshwater fish.