Physiology of fishes

physiology of fishes

1. PHYSIOLOGY OF FISHES by SAFIA Afridi

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.