Fish_Gill.pptx

Fish gill

1. Fishes are aquatic vertebrate. They utilize oxygen for respiration dissolved in water. Gills are the primary respiratory organ in fishes and they are borne in series of gill pouches. The gills are well designed for gas exchange between blood and water. Fish Gill

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3. Gills in agnathous lamperys and hagfishes are in pouches ( Marsipobranch /pouch gills). Each pouch has an internal opening from the pharynx and one that leads to or towards the outside. Other parts of the water route in lamprey and hagfishes include oral vestibule, the mouth and the pharynx. In the hagfishes a pituitary duct connects the exterior with the pharynx dorsally. In the adult lamprey, the pharynx becomes divided from the dorsal food pathway anteriorly by a shelf of tissue, the velum. The ventral respiratory tube thus formed leads to the gill pouches via the internal branchial apertures. Lampreys have seven pairs of external gill openings. Some hagfishes have numerous gill pouches (5-14 in Eptatretus ) on each side, each with an internal and external aperture. In other hagfishes (e.g. Myxine ), the six pairs of gill pouches open on each side into a common duct, which in turn opens to the outside near the level of sixth pouch. Functionally this arrangement parallels the opercular gill covers in Chimaeras and the bony fishes.

4. Every hagfish has a tube ( esophageocutaneous duct) aft of the gill pouches on the left side only. The gill in gnathostomes are carried on branchial arches. In shark and relatives ( Elasmobranch ) the gill are in chambers resembling those of the pouch gill of lampreys and hagfish. The interbranchial septa that separate the chambers in Chondrichthyes which are variously reduced in Osteichthyes where gills of all arches lie in a more or less common chamber. The septa are thus either complete ( Chondrichthyes ) or variously partial ( Osteichthyes ) and each typically bears a hemibranch on each side. Gill filaments in Chondrichthyes are ridge-like folds on the interbranchial septa (Giving name Elasmobranch meaning Plate gill).

5. 6 Hagfish gill pouch

6. Fig. Generalized schematics of gills and associated pouches/arches in hagfishes ( A  and  E ), lampreys ( B  and  F ), elasmobranchs ( C  and  G ), and teleosts ( D  and  H ). All schematics are oriented anterior to posterior, with oral opening at top.

7. Gills in Lampreys and Hagfish The seven paired gill sacs or branchial pouches The gill sacs open toward the lumen of the alimentary canal. Each is divided from the next by a thin diaphragm

8. Gills in Shark and Rays Five, more rarely six or seven external gill slits exist ventrally in a series on each side in rays and their relatives but laterally in sharks. An anterior addition to this series of openings in both shark and rays is the spiracle, corresponding to a vestigial gill slit. Internal to the spiracle, gill lamellae may persist as a hyoidean pseudobranch . In shark, respiratory water typically enters through the mouth, in the bottom dwelling rays the spiracle admits most of water that flows subsequently over the gills. Well developed septa with cartilaginous supports and individual gill-arch. Both primary and secondary gill filament are present in each hemibranch . The primary end s of primary gill filaments are detached from the septum.

9. 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 .

10. Gill rakers Four paired holobranchs tongue

11. OMNIVOROUS In the omnivorous fishes like Puntius sarana, gill rakers are short and stumpy. HERBIVOROUS: Like Labeo rohita,Cirrhina marigala, gill rakers form a broad sieve like structure across the gill slits for filtering the water in order to retain the food in the bucco-pharynx

12. Carnivorous Fishes : Gill rakers are normally long, hard and teeth like forming rasping organs as in Wallago attu, Mystus seenghala, Channa striatus.

13. Gills in Bony fishes Bony fishes have a single external branchial aperture on each side of the head, beneath a gill-covering operculam . Loss of spiracle, reduction of gill slits to four, and deep indentation between the two hemibranch of each holobrance form a transition from lower ( Chondrostei ) to higher ( Teleostei ) rayfin bony fishes. The forked efferent branchial artery of each aortic arch of sharks ( Chondrosteans ) is replaced by a single efferent vessel in teleost . In all bony fishes muscles move the bases of the hemibranchs so that the pressure in and the flow of water from, the oral cavity is regulated. Strong adductions of the two hemibranchs of a holobranch toward one another occur in “coughing”. Coughing is a violent sweeping of water over the gill lamellae to free them from accumulated detritus.

14. Pseudobranch : Although lacking of spiracle, rayfin bony fishs retain a hyoidean pseudobranch that is free in some fishes but skin-covered in others. This portion of gill region is the first to develop in the embryo and probably has an early respiratory function. In adult bony fishes, pseudobranch receives oxygenated blood through a secondarily established blood supply from the aorta and related blood vessel and also has direct connect to the choroid gland of the eye. Pseudobranch is absent in the eels and their relatives, elephant fishes, the cat fishes, featherbacks and other specialized group in which choroid gland missing.

15. Each filament of a pseudobranch has a thin cartilaginous supporting rod and blood vessels in its core, around which are arranged layers of pseudobranch cells and sinusoidal blood spaces. The large granular pseudobranch cells which dominate the epithelium, are covered at the outer edge by squamous pavement epithelial cells. The blood space is supported by pilaster cells, whose thin extensions form the endothelial lining of blood space. Within the pseudobranch cells are large numbers of mitochondria and tubular membrane arrays in close proximity to them. These tubules are extensions of the plasma membrane and display secretory activity. This tubules may the site of production of carbonic anhydrase , which facilitate the formation of carbonic acid from CO 2 and water.

16. The gill comprises of gill rakers , gill arch, gill filaments (Primary gill lamellae and lamellae) (Fig. 5.3a & b ). Each gill filament bears many subdivisions or lamellae that are the main seat of gas exchange. In some fishes, (e.g., eel) acidophilic secretory cells occur at the bases of the lamellae. The free edge of the lamellae are very thin, covered with epithelium and contain a vast network of capillaries supported by pilaster cells. A complete gill is known as holobranch . It consists of a bony or cartilaginous arches. The anterior and posterior part of each gill arch possesses plate-like gill filaments. Each holobranch consists of an anterior (oral) and a posterior ( aboral ) hemi-branch.

17. In teleost fishes, five pairs of branchial arches are present of which first four bear gill lamellae (Fig. 5.4a, b) but the fifth is devoid of gill lamellae and transformed into the pharyngeal bone for mastication of food. It does not play any role in respiration . The gill arch is an important unit and bears primary (gill filament) and secondary lamellae. The branchial arch typically consists of paired pharyngobranchials , epibranchials , ceratobranchials , hypo- branchials and a median unpaired basibranchial . The epibranchial and the ceratobranchial elements of each branchial arch bears two rows of gill filaments of the two hemibranchs of the holobranch , which are the seat of gaseous exchange. It encloses afferent and efferent branchial arteries and veins (Fig. 5.4a and Fig. 5.6a, b, c). It is also provided by nerves. The branches of 9th ( glossopharyngeal ) cranial nerve innervate the first gill, while II, III, & IV arches are supplied by the branches of vagus (10th cranial nerve). It also contains abductor and adductor muscles. Inside it contains gill rakers , taste buds, mucous gland cells and sensory papillae.

18. Gill Raker : It occurs in two rows on the inner margin of each gill arch. Each gill arch is short stumpy structure supported by bony elements (Fig. 5.3a & b). The gill arch projects across the pharyngeal opening. They are modified in relation to food and feeding habits . The mucous cells of the epithelium help to remove sediments from the covering epithelium in order to enable the taste buds to function effectively and to sense the chemical nature of food passing through the gill sieve . Gill Filaments (Primary Gill Lmellae ): Each hemi-branch consists of both primary and secondary lamellae (Fig. 5.5) The primary gill filaments remain separated from the branchial septum at their distal end making two hemi-branch in opposition which direct the water flow between the gill filaments. Amongst dual breathers the heterogeneity in the gill system is more pronounced particularly in the swamp eel, Monopterus , Amphipnous cuchia and climbing perch, Anabas testudineus .

19. Fish Gills Fish gills are arranged for countercurrent flow

20. Lamellae (Secondary Lamella): The each gill filament is made up of secondary gill lamellae which are actual seat of exchange of gases. They are generally semicircular and lined up along both sides of the gill filaments. The lamellae frequency is directly proportional to the dimension and resistance of the gill sieve. The secondary lamellae are having two sheets of epithelium which are separated by space and through these spaces blood circulates. The epithelial sheets are separated by a series of pillar cells. Each cell consists of central body and is provided with extensions at each end (Fig. 5.6d).

21. Branchial Glands: These are specialized cells of the epithelium. They are glandular in nature and perform different functions in normal and experimental conditions. The most common specialized branchial glands are the mucous glands and acidophilic granular cells (chloride cells).

22. Mucous Glands: These gland cells are unicellular. They may be oval or pear shaped with a neck through which they open outside the epithelium. The nucleus lies at the bottom of the cells. They are typical goblet cells. They are present throughout the epithelium, i.e., gill arch, gill filament and secondary lamellae. They secrete mucus which is glycoprotein, both acidic and neutral. According to Ojha and Mishra (1987), acidic and neutral glycoproteins are secreted by same cells suggesting that they undergo transformation from each other. Protective 2. Friction reducing 3. Anti-pathogen 4. Help in ionic exchange 5. Help in gas and water exchange.

23. These cells contain granules, which take acidic stain, hence called acidophlic . They are provided with a large number of mitochondria. These cells are also known as ioncytes because they help in the ionic regulation in the euryhaline and stenohaline fishes. Chloride Cells: Taste Buds: They are flask shaped multicellular structure and distributed in the epithelium of the gill arch region. There are two distinct type of cells, sensory and supporting, and can be distinguished under phase contrast microscope. They help the fish to sense the nature of food particles contained in the water flowing through the gill during ventilation.

24. Respiratory Mechanism: The continuous undulational flow of water over gill surface is accomplished by respiratory pump. It is now unanimously accepted that the respiratory pumps of a teleost consist of buccal cavity and two opercular cavities, caused by movements of bone of arches and operculi , resulting in the pumping action of the system. In the beginning, the water enters into the mouth by expansion of buccal cavity. The water is then accelerated over the gill by the simultaneous contraction of buccal cavity and cavity contracts, expelling the water out through the opercular opening, the cycle begins again

25. Teleost Fishes V P

26. Inspiration:   Muscular contraction exerts in the floor of the pharynx and buccal cavity resulting in buccal cavity expanding. The buccal cavity pressure decreases. Mouth valve opens leading to opening of the mouth and water with dissolved oxygen enters from the outside because of reduced pressure. * At the same time the operculum bulges outwards leading to the opercular cavity expanding. The opercular cavity acquires a negative pressure i.e. pressure reduces therefore opercular valve closes. The expansion of the opercular cavity leads to pressure falling below that of the buccal cavity which has began to contract as a result water is sucked into the opercular cavity from buccal cavity and flows over the gills where gaseous exchange takes place.

27. Expiration: Muscular contraction leads to floor of pharynx raising and buccal cavity continuing to contract. The buccal cavity acquires positive pressure i.e. pressure increases, mouth valve closes and water in then forced from buccal cavity to opercular cavity. There is inward movement of the operculum. The opercular cavity contracts and acquires a positive pressure, opercular valve opens and water containing carbon dioxideis expelled. The pressure in the buccal cavty is higher than that in the opercular cavity. Also a continous stream of water is maintained over the gills throughout most of the breathing cycle by the combined action of the buccal cavity as a suction pump. Apart from the time when both the mouth and opercular valves are open, the pressure in the buccal cavity hence contionous flow of water from the buccal cavity to opercular cavity.

28. Fish employ the countercurrent system to extract O 2 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.

29. Blood flow through lamellae is from posterior to anterior ( back to front ). Water flow over lamellae is from anterior to posterior ( front to back ). Counter-current allows for diffusion from high O 2 in water to low O 2 in blood across entire length of lamella. Countercurrant Close-up!

30. When the blood and water flows in the same direction, the co-current system , it will initially diffuses large amounts of oxygen but the efficiency reduces when the fluids start to reach equilibrium. In the counter-current system, equilibrium is never reached! Result: Oxygen flow is always directed into the gills. % O 2 in water % O 2 in gills % O 2 in water % O 2 in gills

31. Ram ventilation is a simpler process in which a fish swims forward with its mouth open, taking in water that passes over the gills. The drawback to ram ventilation is that the fish has to swim continuously to be able to continue breathing. A lot of sharks breathe this way, as do some large bony fish swimmers like tunas and billfishes. Many fishes, including sharks like the sand tiger shark, can switch between buccal pumping and ram ventilation as the situation and their swimming speed dictates. Some sharks and bony fishes, on the other hand, can’t accomplish buccal pumping at all and have to swim continuously to maintain the water/blood gas exchange. This is obligate ram ventilation. The bony fishes include the aforementioned tunas and billfishes. Obligate ram-ventilating sharks include great whites, makos , salmon sharks and whale sharks. Ram ventilation

32. Respiratory structure other than gill Skin: In some fishes gas exchange takes place across the skin. Diffusion through the skin is known to play an important role in the respiration of larval fish-the larvae of Monopterus albus The skin of adult fish especially those without scale or embedded with small scales can function as respiratory surface- eels ( Anguilla ). 2. Arborescent organ: Clarias batrachus , the walking catfish has accessory respiratory organ which consists of the supra- branchial chamber, the two beautiful rosettes or air trees, the fans and the respiratory membrane are called arborescent organ.

33. 3. Labyrinth organ: Anabas, Trichogaster and Channa spp. possess a labyrinth suprabranchial organ that functions as an air breathing organ. The organ is the forms of highly vascularised plates which are derived from branchial tissue. Air taken in through the mouth passes through the labyrinth where oxygen is absorbed into the blood. 4. Air sac: In Heteropneustes fossilis air breathing organs are in the form of a pair, sac like structure that extends backwards from the region of the gills up to the middle of the caudal region. They are thin-walled, long, tubular structure with highly vascular walls and lie embedded between the myotomes of the body. The opening of the sac is guarded by valve like stucture and the gill lamellae on the arches are reduced. The air sac receive blood from a thick branch of the 4 th afferent branchial vessel of its won side and are drained by means of of the 4 th efferent branchial vessel of the corresponding side.

34. 5. Gut: In some species, parts of the gastrointestinal tract, notably the stomach or the small intestine, have modified to serve a role in respiration. These parts of the gut become highly vascularised which facilitated gas exchange between the blood and swallowed air. e.g. members of the families of armoured catfish, Callichthydae and loricaridae . 6. Gas bladder: The gas bladder is a long cylindrical bag like structure situated within the body cavity. In some species, it functions as an accessory respiratory organ. In these species bladder wall is highly vascularised . e.g. Giant redfish: Arapaima gigas ; Bowfin, Amia calva ; Gars Lepisoteus etc. 7. True lung: In lungfishes ( Dipnoi ) the gas bladder has evolved structurally to resemble a lung. The Australian lung fish Neoceratodus has one lung that lies dorsal to the gut. In the African ( Protopterus ) and South American lung fish ( Lepidosiren ) the lung is paired but ventral to the gut. Both are obligate air breather. Like the lung of higher vertebrates, the lung of these fishes are well sacculated and heavily vascularised .

35. Gas bladder The gas bladder, less precisely designated as the swim bladder or the air bladder is characteristics of true fishes and reaches its fullest development as a hydrostatic organ among spiny rayed fishes. The gas bladder functions also as an accessory breathing organ As a sound producer As a resonator in sound perception. In certain deep sea mouth fish relatives the bladder may also serve as a fat-storage organ of possible buoyant function. In its weight regulating (hydrostatic) function, gas secretion is accomplished through a special structure in the bladder wall, the gas secreting complex with its rete mirabile or wondernet of circulatory vessels and a gas gland.

36. Structure and location Swim bladders can be paired or unpaired gas-filled sacs. The pneumatic duct usually connects to the oesophagus ventrally in dipnoans and chondrostean while dorsally in garfishes, the bowfins, and modern bony fish. Sometimes this pneumatic duct is linked with the pharynx or stomach. Swim bladders are present above the coelomic lining of the peritoneal cavity, below the dorsal aorta and vertebral column, and lies close to the kidney . The walls are made up of elastic tissues and smooth muscles.

37. On the basis of the connection of the pneumatic duct with the gut, fish are divided into two groups: Physostomous fishes: These types of fishes have open pneumatic duct i.e., linked with the gut. E.g. dipnoans, chondrostean , holostean and few teleosts . Physoclistous fishes: These types of fishes have closed pneumatic duct i.e., it is not linked or any connection with gut. e.g., cat fish, carp, eels, herring and salmon. Gases in swim bladder: Different fishes contain different gases in their swim bladder. Some fishes have almost 99% pure nitrogen, while some fishes have 87% oxygen. The swim bladder of all fishes contains at least traces of four gases i.e., nitrogen, oxygen, argon, and carbon dioxide .

38. Basic Structure of Swim-Bladder: The swim-bladder in fishes varies greatly in structure, size and shape: It is essentially a trough sac-like struc­ture with an overlying capillary network . 2. Beneath the capillary system the wall of the anterior part of swim-bladder consists of the following layers outside to inside (Fig. 2.38A 1 ). (a) Tunica externa made up of dense collagenous fibrous material. (b) Sub-mucosa, consisting of loose connective tissue . (c) Muscularis mucosa, consisting of a thick layer of smooth muscle fibres . (d) Lamina propria , formed of thin-layer of connective tissue and (e) Innermost layer of epithelial cells . 3. In the posterior chamber of swim bladder, outside the layer of muscularis mucosa there is a glandular layer. This layer is richly supplied with blood capillaries from rete mirabile (Fig. 2.38A 2 ). 4. The swim bladder opens into the oesophagus by a ductus pneumaticus , which is short and wide in lower teleosts ( Chondrostie and Holostei ), while in others it is longer and narrower. The gas secreted by the swim- bladder is mostly oxygen. Nitrogen and little quantity of carbon dioxide are also present .

39. Functions of Swim bladder Hydrostatic organ: It is primarily a hydrostatic organ and helps to keep the weight of the body equal to the volume of the water the fish displaces. It also serves to equilibrate the body in relation to the surro­unding medium by increasing or decreasing the volume of gas content. In the physo­stomous fishes the expulsion of the gas from the swim-bladder occurs through the ductus pneumaticus , but in the physoclistous fishes-where the ductus pneumaticus is absent -the superfluous gas is removed by diffusion. Adjustable float: The swim-bladder also acts as an adjustable float to enable the fishes to swim at any depth with the least effort. When a fish likes to sink, the specific gravity of the body is increased. When it ascends the swim-bladder is distended and the specific gravity is diminished. By such adjustment, a fish can maintain an equilibrium at any level.

40. Maintain proper centre of gravity: The swim bladder helps to maintain the proper centre of gravity by shifting the contained gas from one part of it to the other and thus facilitates in exhibiting a variety of move­ment . Respiration: The respiratory function of the swim-bladder is quite significant . In many fishes living in water in which oxygen content is considerably low, the oxygen produced in the bladder may serve as a source of oxygen. In few fishes, specially in the dipnoans, the swim-bladder becomes modified into the ‘lung’. The ‘lung’ is capable of taking atmos­pheric air . Resonator: The swim bladder is regarded to act as a resonator. It intensifies the vibrations of sound and transmits these to the ear through the Weberian ossicles .