Osteichthyes is a class of jawed fishes having a bony endoskeleton. It is the largest class of vertebrates and includes a diverse group of marine and freshwater bony fishes.
The other group of jawed fishes are cartilaginous fishes, which are included in the class Chondrichthyes.
Osteichthyes is a class of fishes included in the division Gnathostomata, which includes all the vertebrates having jaws. Jawless fishes are included in the division Agnatha and the class Cyclostomata.
Gnathostomata is divided into two superclasses, viz. Pisces (having fins) and Tetrapoda (bear limbs).
Pisces is divided into two classes:
- Osteichthyes- Bony fishes
- Chondrichthyes- Cartilaginous fishes
Osteichthyes is subdivided into two subclasses:
- Sarcopterygii- lobe-finned fish
- Actinopterygii- ray-finned fish
- With more than 29,000 species of bony fishes, it is the largest class of vertebrates.
- It includes both marine and freshwater fishes, most of the commercially used fishes are included in this class.
- The size ranges from less than 8 mm in Paedocypris progenetica, which is also the smallest known vertebrate to 4 m and weigh about 1500 kg in the ocean sunfish (Mola mola).
- Their endoskeleton is made up of bones.
- Paired and median fins are present, which are supported by long rays of cartilage or bone. Fleshy lobed fins are present in sarcopterygians. These types of fins are supported by bones having joints. These are adapted to live at the bottom of the sea.
- The tail is mostly homocercal.
- They contain swim bladder or air bladder, which provides buoyancy to them and prevents sinking. Swim bladder also facilitates gaseous exchange.
- The mouth is terminal.
- Bony fishes contain four pairs of gills. A protective covering of bony flap known as the operculum protects the gills.
- The sarcopterygians, lungfishes and lobe-finned fishes contain lungs.
- The skin is covered by bony dermal scales known as ganoid, cycloid or ctenoid scales.
- They are poikilotherms or cold-blooded animals and lack the capacity to regulate their internal body temperature. Some of the larger marine fishes like tuna, swordfish, etc. show some level of endothermy.
- The heart is two-chambered, contains one auricle and one ventricle. Lungfishes have a three-chambered heart with two auricles and one ventricle.
- The brain has a small olfactory lobe and cerebellum. There are ten pairs of cranial nerves present.
- The lateral line organ contains hydrodynamic receptors. The sensory unit is called neuromasts. It helps in sensing vibration, water pressure, navigation and locate their prey.
- Cloaca is absent, different genital and anal openings are present.
- They are ammonotelic and have mesonephric kidneys.
- Sexes are mostly separate but some are hermaphrodites. They are mostly oviparous and lay a huge amount of eggs. Fertilisation is mostly external and direct development.
- In male Hippocampus, the brood pouch is present, where eggs incubate.
Some of the prominent examples of bony fishes are:
Marine bony fishes
- Hippocampus (Sea horse)
- Exocetus (Flying fish)
- Lophius (Angler fish)
Freshwater bony fishes
- Labeo rohita (Rohu)
- Labeo catla (Katla)
- Clarias (Walking catfish or Magur)
- Mystus (Catfish)
Aquarium bony fishes
- Betta splendens (Fighting fish)
- Pterophyllum (Angelfish)
Coelocanth Latimeria is a living fossil and the oldest known lineage of Sarcopterygii.
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