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General characteristics of Chondrichthyes and Osteichthyes, Classification up to order Migration Osmoregulation Swim bladder in Fish  What do you wonder about today’s topic?  CHALLENGES OF AQUATIC SYSTEM Ø How to Breathe Ø Adjustin...

General characteristics of Chondrichthyes and Osteichthyes, Classification up to order Migration Osmoregulation Swim bladder in Fish  What do you wonder about today’s topic?  CHALLENGES OF AQUATIC SYSTEM Ø How to Breathe Ø Adjusting Buoyancy Ø Regulation of Ions and Body fluids Ø Response To Temperature How to Breathe Aquatic vertebrates have specialized structures Gills, where oxygen and Carbon di oxide are exchanged. Gills are branching organs located on the side of fish heads that have many small blood vessels called capillaries. As the fish opens its mouth, water runs over the gills, and blood in the capillaries picks up oxygen that’s dissolved in the water. Then the blood moves through the fish’s body to deliver the oxygen, just like in humans. All bony fish also have a bony plate called an operculum, which opens and closes to protect the gills. HOW GILL WORKS  The arrangement of blood vessels in the gills maximizes oxygen exchange. Each gill filament has two arteries, an afferent vessels running from the gill arch to the filament tip and efferent vessels returning blood to the arch. Each secondary lamella is blood space connecting the afferent and efferent vessels. The direction of blood flow through the lamella is opposite to the direction of water flow across the gill. This arrangement is is called countercurrent exchange to assures as much oxygen as possible diffuses into the blood. Gills are made up of two rows of filaments, through which water continuously flows while lungs contains sacs connected to outside through a network of breathing tubes. Gill and lungs are two types of respiratory system in Vertebrates. Generally, they are responsible for the exchange of respiratory gases: oxygen in and carbon dioxide out. Moreover, blood vessels run near them to facilitate gas exchange. Which one is the more efficient system for capturing Oxygen from the surrounding Gills / Lungs ?  Accessory Respiratory Structures Some fishes supplement the oxygen they get from the gills with additional oxygen obtained from the air via the lungs or other accessory structures. Buccopharyngeal Epithelium Skin External Gills Labrinthiform Organs Opercular Lungs Swim Bladder https://www.notesonzoology.com/phylum-chordata/fishes/accessory-respiratory-organs-of-fishes-with-diagram-chordata-zoology/8057 Heteropneustes fossilis: A pair of long, tubular and dorsally situated air-sacs, arising posteriorly from gill-chambers and extending almost up to the tail. They are highly vascular. The air is drawn in and expelled out through pharynx. Anabas testudineus: spacious, suprabranchial cavities as dorsal outgrowths of the two gill-chambers. Each cavity contains a special labyrinthine organ formed of much folded, concentric bony plates developed from the first epibranchial bone and covered with thin vascular mucous membrane. Each branchial outgrowth communicates freely not only with the opercular cavity but also with buccopharyngeal cavity. Air is drawn through mouth into suprabranchial cavities and expelled through opercular opening. Air Bladder: Swim-bladder of higher bony fishes (teleosts) is essentially a hydrostatic organ. But in lower bony fishes (dipnoans and ganoids), the air-bladder acts like a lung to breathe air and is truly an accessory respiratory organ. The wall of bladder is vascular and sacculated with alveoli. Origin and Significance of Accessory Respiratory Organs During the Tertiary and Quaternary period of the Cenozoic era, the oxygen level of the atmosphere and of water was reduced. Due to depletion of oxygen in rivers and swamps, the gills were unable to cope with the requirements of the body. Hence, several teleostean species developed accessory respiratory organs to absorb oxygen from air. Most of the fishes possessing air-breathing organs or accessory respiratory organs are capable of living in highly deoxygenated water of the swamps and muddy ponds infested with weeds. Accessory respiratory organs are capable of maintaining life of the fish in oxygen deficient water. Adjusting Buoyancy The fish is able to rise or sink and maintain its equilibrium or position in water without any muscular effort. In most primitive fishes, the air-bladder serves as an accessory respiratory organ or lung which seems to have been its original function. In Amia and Lepidosteus, the air-bladder serves as both a respiratory organ (lung) and a hydrostatic organ. In the Dipnoi (lung-fishes), the air-bladder resembles closely with the lung of amphibians in structure as well as in Protoptenis and Lepidosiren. The air-bladder in higher teleosts or bony fishes is the most specialised, playing little or no part in respiration, and primarily serving as 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. The air-bladder arises as an outgrowth from the oesophageal region of the alimentary canal. It shows a great diversity in mode of development, structure and function in different fishes. It lies ventral to alimentary canal in Polyptens, laterally in Dipnoi and dorsally or dorsoventrally in teleosts https://www.biologydiscussion.com/wp-content/uploads/2016/07/clip_image002-328.jpg Depending on the presence of the duct (ductus pneumaticus) between the air-bladder and the oesophagus, the air-bladder in fishes can be divided into two broad categories- Physostomus and Physoclistous types. Respiration: In many species the amount of oxygen stored in the bladder would enable the fish to survive for a few minutes only, the air-bladder may be more important in deep water fishes where the amount of oxygen stored is much higher. Auditory Function: Air-bladder serves to transmit sound waves to the ear especially in the Ostariophysi, more efficiently than in the species in which a connection with the ear is missing. In Cypriniformes, a series of small bones, the Weberian ossicles, connect the air-bladder and perilymph cavity containing internal ear. Low frequency vibrations of the contained gas, induced by noises in water, are transmitted by the ossicles to the membranous labyrinth. Thus, these fishes can hear. Sensory function:When the fish is subjected to pressure changes by moving into different depths of water, compression of the wall of the air-bladder which functions as a pressure receptor like a manometer, barometer or a hydrophone. It has been suggested that the air-bladder serves as a sense organ enables a fish to maintain a steady depth. Regulation of Ions and Body fluids Osmoregulation in Marine Elasmobranchs: The common examples of marine elasmobranchs are sharks and rays. The salt concentration in their body fluid is roughly one- third the level of the sea-water, but they still maintain osmotic equilibrium. This is achieved by adding to the body fluids large amount of organic compounds primarily urea. Addition of different organic compounds in the body fluid/blood makes the osmotic concentration equal or slightly above the sea-water. Urea is the end product of protein metabolism in vertebrates. Generally it is excreted through kidney, but the shark kidney actively reabsorbs this. But urea can pose problems in the body functioning. It is known that urea destabilizes many proteins, especially enzymes. This problem is solved in elasmobranch by the presence of another organic substance trim-ethylamine oxide (TMAO). TMAO inhibits the effect of urea on enzymes.  In addition, ionic imbalance also observed with respect to sodium ions. Sodium enters into the body primarily through the thin epithelium of the gill and then through the ingested food. This enhances the sodium level in the body, which must have to be excreted or eliminated from the body. Part of the sodium excretion is undertaken in the kidney. Major excretion of Na+ is performed by a special rectal gland. A small gland opens into the posterior part of the intestine, the rectum. The gland secretes a fluid with high sodium and chloride concentrations, which is higher than the sea-water concentration. Osmoregulation in Freshwater Elasmobranchs: Their blood concentrations are lower than those of strictly marine forms. The urea concentration is reduced to less than one third of the value of marine sharks. The problem of osmotic regulation is reduced due to the low level of solutes in the blood. The osmotic inflow of water is diminished because lower salt concentration is easier to maintain. The reduced osmotic inflow of water gives less water to be eliminated by the kidney. Osmoregulation in marine Teleosts: Marine fishes are hyposmotic with the environment. Their main problem is losing body water to the more concentrated sea-water. The body water comes out through their body surfaces, in particular the large gill surfaces. These fishes compensate their inevitable water loss by drinking sea-water. Drinking of sea-water may impose large amount of salts to be ingested and absorbed through the intestine. So salt concentration of the body increases. So, salts must be excreted in a higher concentration than in the water taken in. Gills have dual function in these kinds of organism—one, participation in osmoregulation and second, gas exchange. The secretion of salt through gill is an active process, i.e., energy mediated. The ion transport is carried out, not by the general epithelial cells of the gills, but specifically by some large cells known as chloride cells. These cells are also present in the opercular cover of the fish. These cells actively transport chloride ions. Osmoregulation in Fresh Water Teleosts The osmotic concentration of the blood of freshwater teleosts is much higher than the surrounding water (~300 mOsm/litre). Therefore, their major problem is the osmotic water inflow. To compensate the problem Skin is less important in transporting water inside the body, because it is less permeable. The large volume of water is excreted as urine, which is very dilute and may be produced in quantities up to one-third of the body weight per day. So large urine volume also causes a substantial loss of solutes. This loss is replaced by the gills, which is also slightly permeable to ions. Some solutes are taken in with the food, but the main intake is by active transport in the gills. Large acidophilic cells, the chloride secreting cells or chloride cells are found in the gills and oral membrane of marine and freshwater teleost. Cl- is co-transported by Na+, K+ / Cl- co-transporters and secreted passively by these cells and rate of secretion is directly related to the number of chloride cells and Na+ also transported by active (Na+ K+ ATPase) and co transportation. In fresh water teleosts, Chloride cells work in reverse (Absorption of Na+ and Cl- ions ). Ammonia & bicarbonate ion exchange mechanisms occurs in Chloride cells of freshwater gills Gnathostomes Body Plan Possession of Jaws: It allow variety of new feeding behaviors, including the ability to grasp objects firmly, and along with teeth enable the animal to cut food to pieces small enough to swallow or to grind foods. New food resources only possible with the evolution of Jaws. A grasping movable jaws permits manipulation of objects like jaws are used to dig holes, to carry pebbles and vegetation to build nests, to grasp mates during courtship. Jaws and Teeth: Bony fishes and tetrapods have teeth embedded in the jawbones. However, because teeth form, from a dermal papilla they can be embedded only in the dermal bones and cartilaginous fishes lack dermal bone. Teeth in cartilaginous fishes form from the skin resulting in a tooth whor that rests on the jawbones bot not embedded within it. Developmental studies support the notion that first teeth were not oral structures but were located in the pharynx. Origin of Fins Fins acts as hydrofoils, applying pressure to the surrounding water. As water is incompressible, force applied by the fin in one direction against the water produces a thrust in the opposite direction. A tail fin increase the area of the tail, giving more thrust during propulsion and allow the fin to exert the force needed for rapid acceleration. Unpaired fins in the midline of the body control the tendency of fish to roll or to rotate around the axis of the body. The paired fins can control the pitch and acts as brakes and are specialized to provide the thrust daring swimming like the enlarged pectoral fin of Skates and Rays. The basic form of fin is for tribasal condition. This means that three main elements within the fin articulate with the limb girdles within the body. Fins are also used in defense, may become system to inject poison. Colourful fins are used as visual signals to potential mates, rivals and predators. Origin of Fins Types of Caudal fins or Tails https://biologyeducare.com/fish-fins-its-types-and-functions/ https://www.notesonzoology.com/phylum-chordata/fishes/fin-system-of-fishes-with-diagram-chordata-zoology/8041  Class Chondrichthyes: Cartilaginous Fishes Sharks, rays, skates, and ratfishes Endoskeleton of cartilage Paired fins, movable jaws, gill slits Rough sandpaper – like skin placoid scales pointed tip that is directed backward  Class Osteichthyes: Bony Fish Largest group of living vertebrates Gills covered by operculum Usually swim bladder Highly maneuverable fins Cycloid scales  Osteichthyes: Bony Fish Sub Class Sarcopterygii (lobed – fin finned) Sub Class Actinopterygii (ray – finned)  Sub Class Sarcopterygii (lobed – fin finned) Fins supported by main axis of bone Modified swim bladder – Breath air  Sarcopterygii (lobed – fin finned) Coelacanth – Were thought to be extinct but were rediscovered in West African waters – Coelacanth species are thought to be ancestors of amphibians