Respiration in Fishes PDF

Respiration in Fishes Respiration catabolic process in which the respired oxygen is used in the oxidation of food resulting in the release of energy. This energy is utilized for all the vital activities. Carbohydrates are mainly concerned with release of energy. Oxygen required for this...

Respiration in Fishes Respiration catabolic process in which the respired oxygen is used in the oxidation of food resulting in the release of energy. This energy is utilized for all the vital activities. Carbohydrates are mainly concerned with release of energy. Oxygen required for this process is obtained from the surrounding medium. Carbon dioxide formed in this process of respiration is expressed as follows. On the basis of availability or non-availability of oxygen, respiration is differentiated into two kinds: 1. Aerobic respiration involves utilization of oxygen from the environment and liberation of energy into carbon dioxide. This type of respiration takes place in most of the plants and animals. The organisms which exhibit this type of respiration are termed as aerobes. 2. In anaerobic respiration, glucose is metabolized to lactic acid, without the involvement of oxygen and there is no formation of carbon dioxide. This type of respiration occurs in certain bacteria, parasitic animals etc. Such organisms are known as anaerobes. Life in the absence of oxygen is called anaerobiasis.  The gaseous exchange of oxygen and carbon dioxide taking place between blood and water (or air) through the medium of respiratory organs, is called the external respiration to distinguish it from the internal respiration which refers to the essential transfer of gases between blood and tissues or cells of the body and brings about release of energy. The main respiratory organs in a fish are the gills.  The lateral walls of the pharynx are perforated by means of a series of slit-like apertures, the first of which is called the spiracle (in sharks), lying between the mandibular and the hyoid arches. The second or the hyoidean cleft lies between the hyoid arch and the first branchial arch, while the rest of the gill slits are situated between the proceeding branchial arches. The anterior and the posterior wall of each gill slit is raised in the form of vascular filamentous outgrowths to form the gills where exchange of dissolved oxygen and carbon dioxide takes place. Besides the gills, other structures as the skin, air bladder and accessory organs also function as respiratory structures in some fishes  Types of Gill 1. Holobranch A complete gills or a holobranch consists of a gill arch supported by cartilage or bone. Each arch bears gill rakers towards the inner side, and vascular plate-like filaments projecting towards the outside. Each row of these filaments forms a hemibranch or half gill. A holobranch carries two hemibranchs. In elasmobranches, five pairs of branchial clefts are usually present (first is the spiracle), but only four pairs of gill slits are present in the bony fishes, and the spiracle is also absent. Teleosts have a single external branchial apert you are on each side of the head due to the development of an operculum covering the gills. 2. Pseudobranch In many actinopterygians, a hyoidean pseudobranch consisting of a series of gill filaments is present anterior to the first gill, as in Catla catla. It receives oxygenated blood directly from the dorsal aorta and has a vascular connection with the internal carotid artery. It may serve to increase the oxygen concentration in the blood going to the brain and the eye through the internal carotid artery. The pseudobranch may also be useful in the filling of gas bladder and in the regulation of intraocular pressure. Structure of a teleostean gill – four pairs of gills. Each gill has: Gill rakers – project along the inner surface of the gill arch. ✓Prevent food particles from entering the gill slits or may be specialized for filtering the water in filter feeding fishes. ✓Developed in various degrees and may be soft, thin, thread-like or hard, flat and triangular, or even teeth-like, depending upon the food and feeding habits of the fish. ✓ The also has taste buds that help the fish in detecting the chemical nature of the water flowing through the gill slits.  Gill arch – cartilaginous or bony structure which support the gills. ✓ Bears 2 rows of slender fleshy projections called gill filaments. ✓ Each gill or branchial arch encloses an afferent and an efferent branchial vessel and nerves ✓Each gill arch bears two rows of gill filaments or primary gill lamellae. Gill filaments or Primary gill lamellae – two pairs of gill filaments per gill arch - rich supply of capillaries, contains rows of thin plates or dishes called secondary lamellae. Secondary lamellae – increase the surface area through which gas exchange can take place. The more active the fish is in swimming, the greater the number of lamellae. ✓The relative number and size of the gill lamellae determines the respiratory area of the gill in the fish. ✓The total respiratory area varies with the habits of the fishes generally, fast swimming fishes have more gill area and a larger number of gill lamellae per mm of gill filament, than the sedentary species. ✓The efficiency of the gill as a respiratory organ is also depends on the diffusion distance i.e., the barrier through which exchange of gases takes place between blood and water. ✓ The water breathing fishes have a higher diffusing capacity due to larger gill area and small diffusion distance, than the air breathing fishes which have smaller gill area and a larger diffusion distance Respiratory pathway and Non-respiratory or Nutritive pathway. The respiratory pathway is associated with respiration. Blood is oxygenated in teleosts by rhythmical inhalation and exhalation of water through the bucco-pharyngeal cavity. This is effected by suction of water into the cavity and its subsequent expulsion through the gill slits, during which the water bathes the highly vascular gill Iamellae. The bucco-pharyngeal cavity therefore applies both suction and pressure to propel water through the gills.  Cartilaginous fishes like sharks allow water in by opening the mouth, which is then closed. The rising of the floor of the mouth causes water to be pumped through the gills and deoxygenated water goes out by way of the separate gill slits. The spiracle also allow water to move in.  Bony fishes are more efficient because of the presence of operculum, which close as the ppharynx expands, sucking the water in. ✓The closing of the mouth and opening of the opercula force water through the gills and out. Fast swimming species may leave their mouth and opercular aperture widely open so that the gills are bathed by a continuous current of water produced by swimming. ✓In general, the gill cavities of fast swimmers are smaller than those of sedentary species.  Afferent branchial vessel brings oxygen deficient blood into the gill gill arch primary gill secondary gill lamella break up into capillaries where exchange of gases takes place countercurrent gas exchange from the water irrigated through the gills is transferred to deoxygenated blood oxygenated blood is collected by the efferent lamellar primary efferent vessel of the primary gill lamella efferent branchial vessel of the gill arch to the body  Countercurrent gas exchange - diffusion of oxygen from sweater to blood is enhanced because the water that flows across the lamellae in the opposite direction to that of the blood. ✓The concentration of oxygen (indicated by dots) is always higher in the water than in the blood. If circulation were not reversed, blood to the body would have less oxygen.  The non-respiratory pathway consists of a complex arrangement of sinuses and veins that carry the blood direct to the heart, by-passing the systemic circulation. ✓Its function is believed to provide nutrition and oxygen to the filament tissue, and may also be associated with the circulation of hormones. ✓This pathway cosists of the efferent filament artery, nutritive blood channel, central venous sinus, venules and the branchial veins.  Other organs for Respiration - fishes that actually leaves the water and breathe air are called bimodal breathers. Air-breathing fish in aquatic habitats often breathe synchronously, presumably to minimize individual by terrestrial predators. Following adaptive mechanisms called aquatic surface respiration: 1. modification of the gills labyrinth organ – suprabranchial accessory breathing organ that allows fish to take in oxygen directly from the air. Clarias batrachus. The walking catfish have thickened, widely spaced lamellae on the dorsal side of the filaments and branched bulbus dendritic structure dorsally emanating from the 2nd and 4th gill arches. 2. use of the skin cutaneous respiration – gas exchange across the water at capillaries located throughout the body Eels are the ones basically utilizing their skin for respiration in addition to their gills. By diffusion through a well-vascularized skin and to a lesser extent across the gills, they are able to use atmospheric air for respiration 3. Mouth Electric eels (Electrophorous electricus) in contrast to “true eels”, are among the obligate “air breathers”. It has a well- vascularized area in the buccal cavity where most of its required oxygen is taken up. ✓The buccal cavity has a large surface area from surface convolutions and pappilae, thus, the gills have generated over evolutionary time. Anabas has also modified its mouth parts for aerial respiration Obligate air breathers – must rise to the surface every 10 minutes or so to inhale before returning to the bottom, ~80% of oxygen is obtained this way Facultative air breathers – optional – use air breathing to supplement aquatic respiration 4. Gut catfish as in Haplosternum, Anicistrus and Plecostomus have parts of their gut specialized for oxygen uptake by actually swallowing air. While oxygen is taken by way of gut, carbon dioxide is released in the gills. 5. True lungs (Dipnoi) of South America and Africa are obligate air breathers. They survive an extremely dry period by aestivation and take air through a small vent made in the mud. They have well-acculated and heavily vascularized lungs (subdivided into air sacs maximizing surface area for gas exchange). Carbon dioxide is released through a vestigial gill. Eastivation or estivation – like hibernation but in dry conditions – become inactive and stop feeding in response to warm temperature 6. Swim bladders Bichir (Polyoterus), bowfin (Amia), gars (Lepisosteus) use swim bladders for gas exchange. Fish need energy to: a. move b. find food c. reproduce d. digest food e. maintain body and internal environment Factors affecting oxygen-consumption uptake or rate: 1. life stage ✓ fish eggs use very little oxygen until they hatch. 2. body weight ✓Among juvenile and adult fishes, larger fish use more total oxygen/hr than smaller fish do because of the greater total metabolic demands of more tissue mass 3. level of activity ✓ Swimming fish use more oxygen than resting ones because extra metabolic demands of exercising red swimming muscles. 4. environmental temperature ✓In waters with adequate dissolved oxygen, fish in warmer water generally have higher oxygen consumption rates than those in cooler waters, because warmer temperature typically increase the cellular nutrient and oxygen (metabolic) demands of ectotherm organisms. 5. feeding ✓Oxygen consumption rates increased 41% to 48% to 130% over resting rates after feeding in Pacific cod and juvenile northern pike, respectively. This extra energy (usually termed as specific dynamic action of SDA) is needed for digestion and growth.  LESSONS FROM RESPIRATION ✓Water severely limits oxygen solubility, yet fishes have evolved respiratory structures and mechanisms that allow them entry into virtually all aquatic and even some terrestrial-environments. ✓Most fish breathe water using efficient gills, and oxygen diffuses across respiratory membranes following the P02 gradient. ✓Fishes' requirements for oxygen vary with species, size, activity level, and important water conditions, including temperature. ✓ fishes have evolved the ability to breathe oxygen-rich air, thereby freeing them from hypoxic water constraints but also forcing them to deal with terrestrial predators when they breathe.