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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:

  1. Osteichthyes- Bony fishes
  2. Chondrichthyes- Cartilaginous fishes

Osteichthyes is subdivided into two subclasses:

  1. Sarcopterygii- lobe-finned fish
  2. Actinopterygii- ray-finned fish
Kingdom Animalia
Phylum Chordata
Subphylum Vertebrata
Division Gnathostomata
Superclass Pisces
Class Osteichthyes
  • 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 a swim bladder or air bladder, which provides buoyancy to them and prevents sinking. The swim bladder also facilitates gaseous exchange.
  • The mouth is terminal.
  • Bony fishes contain four pairs of gills. A protective covering of a 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 locating 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 the male Hippocampus, the brood pouch is present, where eggs incubate.

Some of the prominent examples of bony fishes are:

Ray-finned fishes

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)

Lobe-finned fishes


  • Lepidosiren
  • Neoceratodus
  • Protopterus

Coelocanth Latimeria is a living fossil and the oldest known lineage of Sarcopterygii.

This was all about Osteichthyes. For more such topics related to NEET, visit BYJU’S. Check NEET Biology Flashcards for the revision of important concepts.

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Frequently Asked Questions

Is Osteichthyes mouth terminal?

Yes, the mouth of Osteichthyes is terminal

Does Osteichthyes have teeth?

Yes, the presence of teeth is one of the characteristics of Osteichthyes.

Are sexes separate in Osteichthyes?

Males and females are born separately in Osteichthyes but there are some species that are hermaphrodites.

Does Osteichthyes have ventral mouth?

The mouth, gill slits and nostrils are found on the underside or ventral side of Osteichthyes.

How does Osteichthyes protect themselves?

The Osteichthyes have a layer of scales to protect themselves.

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