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The below mentioned article provides biology notes on Class Osteichthyes.
1. The endoskeleton is cartilaginous in the embryonic stage, but in the adult forms more or less it is replaced by bones. Thus they have bony endoskeleton. They are ectothermic (cold blooded). There are about 25,000 species of bony fishes.
2. Caudal fin usually homocercal symmetrical (Gr. homos- alike).
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3. The exoskeleton, if present comprises cycloid, ctenoid or ganoid scales, which are dermal in origin.
4. The mouth is terminal. Digestive tract leads into an anus. Cloaca is absent in bony fishes.
5. External nares lie on the dorsal surface of the snout. In lung fishes internal nares are also present.
6. Bony fishes have a sac-like outgrowth, the swim bladder (also called air bladder), arising from the dorsal wall of the oesophagus, which is air-filled organ, used to maintain balance and to swim up and down. In some fishes, such as Heteropneustes, it helps in respiration.
7. They have 4 pairs of gills which are covered by an operculum on each side.
8. The heart is 2-chambered (one auricle and one ventricle) and also has sinus venosus and conus arteriosus. Lung fishes have three chambered heart. (Two auricles and one ventricle). Bony fishes have well developed renal portal system. RBCs are oval and nucleated.
9. Kidneys are mesonephric. Ammonia is chief nitrogenous waste.
10. There are present 10 pairs of cranial nerves.
11. The brain bears relatively small olfactory lobes and cerebellum.
12. Lateral line system is well developed.
13. They have internal ears which helps the fish keep its balance. The nictitating membrane in the eye of fish is well developed.
14. Fertilization is generally external. Most forms are oviparous, some are ovoviviparous. Development is direct except in Anguilla where development is indirect with a larva lepto- cephalus. Some bony fishes show parental care.
15. Bony fishes occur in all sort of waters— fresh, marine, brackish.
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Examples:
Marine Fishes — Exocoetus, Hippocampus, Solea, Echeneis (Sucker fish), Lophius (Angler fish).
Fresh Water Fishes — Labeo, Catla, Clarias (Magur), Anguilla, Anabas, Mystus,
Heteropneustes Wallago, Lung fishes.
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Aquarium Fishes — Betta (Fighting fish), Pterophyllum (Angel fish).
Carps:
Carps have toothless mouth with scales on the body; however, head is without scales. Barbels are normally absent, if present, are small or rudimentary. They are mostly herbivorous.
Carps are of two types:
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(i) Major Carps:
They are bigger in size and their growth rate is faster, e.g., Labeo rohita, Labeo calbasu, Cirrhinus mrigala, Catla catla, Ctenopharyngodon idella (Grass carp),
(ii) Minor Carps:
They are smaller in size and their growth rate is slower, e.g. Labeo bata.
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Cat Fishes:
They do not have scales but have well developed barbels. Teeth are mostly well developed. They are carnivorous, e.g., Mystus seenghala, Clarias batrachus (Magur), Heteropneustes fossilis (Singhi), Wallago attu (Fresh Water Shark), Rita rita.
Murrels (Snake-Headed Fishes)
They have snake-like head). Scales are present both on body and head. They are carnivorous, e.g., Ophiocephalus (- Channa) punctatus. Live fingerlings (2″ size) of Channa species are used in Hyderabad once every year (in June) to cure asthma free of cost. The mouth of fingerling is filled with some herb and the patient is made to swallow it. However, no scientific explanation of this fish therapy is known.
Labeo Rohita (Rohu):
It is found in clear and sluggish rivers and streams. The adults are chiefly herbivorous in diet. The young ones are planktivorous. Two short threads like structures, the barbels, are present. The tail is homocercal. This fish serves as a popular delicious dish.
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Catla Catla (Theila):
It is a fresh water fish inhabiting all the rivers in India. It feeds on plankton and decayed vegetables. The trunk and tail bear moderate sized scales. Barbels are absent. Catla catla is an excellent food fish.
Anabas— The Climbing Perch:
It can live out of water for some time, where it respires through accessory respiratory organs lying in-front of the gills. It is carnivorous predatory fish it is very fond of eating earthworms. It is unable to climb trees. Birds may pick it up from land and drop on trees. This has led to its common name— climbing perch. The climbing perch is a good food fish.
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Mystus: The Cat Fish:
Mystus seenghala is a common fresh water cat fish. It is carnivorous predatory fish feeding exclusively on small fishes, fish fry and prawns. Elongated body is without scales. The snout bears four pairs of barbels. This fish is also eaten.
Anguilla (Fresh Water Eel):
It has a long snake like body. Skin has rudimentary scales. Adult male and female fishes migrate from river to sea where they lay eggs and die. The young which hatches from egg is called leptocephalus (larva of eel). The larvae are so transparent that they are called glass fishes. They feed and grow in sea for 2 or 3 years, then enter the river and undergo metamorphosis to become adults.
Exocoetus (Flying Fish):
In fact, it does not fly but often leaps into the air up to about six metres high. It is an excellent food fish. The pectoral fins are modified into wing-like structures, with the help of which the fish glides.
Hippocampus (Sea Horse):
The neck and the head of the fish are horse-like and the tail is prehensile. The fish always swims upright in sea water. The sea-horse exhibits sexual dimorphism.
The male bears a brood pouch in which the female lays eggs and the latter remain there till they hatch. Thus, the parental care is performed by the male. The pelvic and caudal fins are absent. The dried skin of the sea horse is used for the preparation of some ornaments.
Solea (Flat-Fish):
It is interesting to note that in the early development of the embryo, the eyes of these fishes are laterally situated but being a bottom dweller they are shifted towards one side, as an adaptation to water pressure.
Gambusia Affinis (Mosquito Fish):
It feeds on the mosquito larvae; therefore, it is widely used to control mosquito larvae. Gambusia is also called larvicidal fish. It is a fresh water fish and shows sexual dimorphism.
Lung Fishes:
There are three genera of living lung fishes: Neoceratodus, Lepidosiren and Protopterus. All have three chambered heart (two auricles and one ventricle).
1. Lepidosiren (South American Lung Fish):
It is found in river Amazon and Paraguay basin in South America. Gills are weakly developed. Respiration is supplemented with two lungs. It undergoes aestivation during summer season.
2. Protopterus (African Lung Fish):
It lives in rivers and large lakes of tropical Africa. Gills are weakly developed. Respiration is supplemented with two lungs. It also undergoes aestivation.
3. Neoceratodus (Australian Lung Fish):
It is found only in the Burnett and Mary rivers of Queens-land in Australia. It respires exclusively by gills and uses its single lung only under stress.
Latimeria (Coelacanth):
It is a “living fossil” which was taken off from the eastern coast of South Africa, on December 22, 1938 by some fishermen. Fishermen brought the specimen to Miss Courtenary Latimer, Curator of the local museum. When she failed to identify it, she sent its sketch to Professor J.L.B. Smith, an eminent Ichthyologist of Rhodes University College at Grahams town.
He recognised it as surviving member of Crossopterygii (subclass of class Osteichthyes) and named it Latimeria chalumnii after the discoverer and locality.
Its discovery is of special interest, because it is believed that crossopterygians (fleshy finned fish) were the ancestors of the first amphibians. Latimeria is believed to be the oldest amongst living fishes. (Now this fish is not alive). It is a connecting link between fishes and amphibians.
