Osteichthys - The Bony Fishes
The endoskeleton is cartilaginous in the embryonic stage, but in the adult forms more or less it is replaced by bones. They are ectothermic (cold blooded). Other characters are :
- Caudal fin usually homocercal.
- The exoskeleton, if present comprises cycloid, ctenoid or ganoid scales. Scales are mesodermal in origin.
- The mouth is terminal. Digestive tracts leads into an anus. Cloaca is absent in bony fishes.
- External nares lie on the dorsal surface of the snout. In lung fishes internal nares are also present.
- A swim bladder is usually present. It facilitates floating and may function as a respiratory organ. As a result a bony fish can stay at a particular depth without expending energy in swimming. Contrary to the cartilaginous fishes.
- Bony fishes use pectoral, pelvic, dorsal, anal and caudal (tail fin) in swimming.
- Indian fresh water fishes which are used as food are catla, rohu, mrigal, kalbasu and the marine fishes used in food are pomfret, Bombay duck and Indian Salmon.
- Neuromast organs are - Rheoreceptor (Sensitive or vibration).
- Gills are covered by an operculum.
- The heart is 2- chambered and has sinus venosus and conus arteriosus. Lung fishes have three chambered heart. (Two auricles and one venricle). They have well developed renal portal system.
- Kidneys are mesonephric. Ammonia is chief nitrogenous waste.
- There are present 10 pairs of cranial nerves.
- Lateral line system is well developed associated with internal ear.
- Fertilization is generally external.
- Bony fishes occur in all sort of waters - fresh, marine, brackish. There are about 25,000 species of bony fishes.
(a) Freshwater Species
- Labeo rohita (Rohu)
- Labeo calbasu (Calbasu)
- Catla catla (Catla)
- Cyprinus carpio (Carp)
(b) Marine Species
- Harpodon (Bombay Duck)
- Anguilla (Eil)
- Sardinella (Salmon)
- Hilsa (Hilsa)
Some air-breathing fishes, used their paired fins to move about on land, gave rise to the first land vertebrates. A living fossil of this group is Latimeria, a lobe-finned fish.
Examples: Anguilla-Eil fish, Labeo-Rohu, Hippocampus-sea horse, Anabas-climbing perch/koi, Gambusia-mosquito fish. Neoceratodus-Australian lung fish, Protopterus-African lung fish, Lepidosiren-American lung fish, Solea-flat fish. Exocoetus (flying fish) Hippocampus (horsefish), Clarius (Magur), Aquarium - Betta (Fighting fish), Pterophyllum (Angel fish)
Exocoetus (Flying Fish)
In fact, it does not fly but often leaps into the air up to about six meters high. It is an excellent food fish. The pectoral fins are modified into wing-like structures, with the help of which the fish glides. It is found in tropical and warmer parts of Atlantic and Indian oceans.
Hippocampus (Sea horse)
The neck and the head of the fish are horse-like and the tail is prehensile. The male bears a brood pouch in which the female lays eggs and the latter remain there till they hatch.
Labeo. Labeo rohita and Labeo calbasu are the common fresh water edible carps. It is covered by large overlapping scales. Head is scale less with sub terminal mouth and a pair of short barbles. The fish is herbivorous but in the juvenile stages it is carnivorous.
Cat Fish. Indian Cat Fish (Clarius batrachus) lives in ponds. It is carnivorous. The head bears sensory threads called barbels. The body is smooth and without scales. Other fresh water cat fishes of India are Mystis seengala (=singharee), Rita rita and Wallago attu (=Mullee).
Climbing Perch (Anabas testudineus). Head bears a number of small spines in front of eyes and along the opercular margins. Dorsal and ventral fins have stiff rays in the anterior region and soft rays in the posterior region. The fish can come out of water and creep on land by means of operculum and pectoral fins in search of small animals. Here it is often picked up by birds and taken to their nests (hence the belief of climbing). For remaining out of water, the fish gulps in air and stores it in accessory respiratory chambers.
Remora. The anterior parts of dorsal fin is modified into sucker for fixing to the undersurface of shark. Remora feeds on the left-over of shark's prey. The relationship is that of commensalisms.
Latimeria chalumnae (The coelacanth). It was first caught in 1938 off the east coast of South Africa. It swims by curious rotating movements of its pectoral fins. All its fins except the anterior dorsal are lobed (each fin is borne on a fleshy, lobe like, scaly stalk). The fish have many primitive features. It is the oldest living fish; and has survived till today without undergoing any change in it. It is therefore described as the living fossil. It belongs to the group crossopterygii from which amphibians are thought to have evolved.