The bony fish possess the bony skeleton and are very different from the cartilaginous fish. It lives in both freshwater and marine habitats. There are three superclasses of fish species: Chondrichthyes (cartilaginous fish), Osteichthyes (bony fish), and Agnatha (jawless fish). Examples of Specific, sensible and latent heat. Chondrichthyes and osteichthyes are the main two taxonomic classes of the fishes, cartilaginous and bony fish respectively.
It arises from the dorsal wall of the esophagus which is used to maintain balance and to swim up and down.The exoskeleton is dermal in origin if present which is composed of cycloid, ctenoid or ganoid scalesThey possess a terminal mouth which is located at the anterior tip of the body.They have well developed lateral line system which runs through the body and consists of a series of sensory organs, called neuromasts that help to sense both water pressure and vibrations.Generally, their fertilization is external with direct development. Most of the fishes are oviparous but some are ovoviviparous.This subclass contains 6 extant species under two orders: Ceratodontiforms and Lepidosireniformes.The largest lungfish is the African lungfish which can reach up to 2 m (6.6 ft) in length and 50 kg (110 lb) in weight.They are omnivorous and their foods consist of fish, insects, worms, crustaceans, mollusks, amphibians and plant matter, etc.They have typically paired fins which act as support against the floor of the water body.The largest member of this subclass is the West Indian Ocean coelacanth which can grow up to 2 m (6 ft 7 in) in length and 110 kg (240 lb) in weight.The fins are supported by rays or spines which give the name ‘actinopterygians'.The unique features of the ray-finned fish is the swim bladder which helps them to move up or down in the water body.The gills are covered by an operculum and the fish perform respiration through gills.They inhabit a variety of environments such as marine and freshwater within 1 to 7000 m depth ranges.They have different types of scales such as ganoid and laptoid scales (cycloid and ctenoid).They have branchiostegal rays which are originated from the bones at the base of the branchial cavity.They have homocercal tail fin where the upper and lower lobes are the same length.They have a well-developed electroreceptive system.They have 5-7 pairs of gills for performing respiration with no operculum.They produce large-sized yolky eggs and their fertilization is internal with direct development.The fish bears one or two nostrils which never opens in the mouth cavity.The heart bears a contractile conus arteriosus with rows of valves.The members of the Elasmobranchii have no swim bladders.They have 5-7 pairs of gill clefts which open individually to the exterior.A tapetum lucidum tissue layer is present in the eyes.They have a thin and long tail with large pectoral fins.The front side of the dorsal fin bears an erectile spine.The body is rounded and tapered at the ends (fusiform body).They are found in either marine or freshwater habitats.Digestive tract leads into the anus with no cloaca.They have well-developed eyes with the nictitating membrane.They have an air-breathing organ which opens to the esophagus.They have long and tubular pelvic and pectoral fins.Its dorsal and anal fins are fused with caudal fin.The upper jaw is fused to the braincase with fused teeth.Their digestive tract contains an intestinal spiral valve.The caudal fin is either diphycercal or heterocercal types. They are cold-blooded animals but only the opah (There are two main groups of fish, namely Chondrichthyes and Osteichthyes based on the composition of the endoskeleton. Rays are viviparous while skates are oviparous. The world`s largest member of Chondrichthyes is the plankton-feeding whale sharks (It is the largest class of subphylum Vertebrata which contains approximately 28,000 known species that comprise 96% of all fishes. The endoskeleton of Chondrichthyes is made up of cartilages and they mainly live in marine habitats while the endoskeleton of Osteichthyes is composed of bones which are found in both marine and freshwater habitats.It is a diverse group which contains more than 700 species, found throughout the world's marine environments.
They have a cartilaginous skeleton with high compressed head and small narrow mouth which gives the head a parrot-like appearance.They have simplified gut with no stomach where the stomach is merged with the intestine.In nature, they inhabit close to the bottom and their foods mainly consist of mollusks and other invertebrates.They bear paired (pectoral and pelvic fins) and unpaired fins (dorsal, anal, and tail fins).They have 4 pairs of gills or breathing organs which are covered by the gill covers or the operculum on each side.They have sac-like outgrowth which is known as swim bladder or air bladder that also acts as a hydrostatic organ. It is also an important part of a healthy diet of all stages of people and controls many diseases. This group includes the sharks, rays, and skates, and their skeleton is made up by rubbery cartilage, which is very light and flexible.