The document describes osteichthyes, or bony fish, which are characterized by their bony skeleton, paired fins, and gills for respiration, with approximately 26,000 species in various freshwater and marine environments. It details their reproductive methods, classification into different orders and subclasses, and their evolutionary history, which includes significant events in the Devonian period and the discovery of the coelacanth in 1938. Additionally, it outlines the key characteristics and adaptations of bony fish, including their skin, scales, heart structure, and buoyancy mechanisms.

1. Class: Osteichthyes
Fish are all members of the phylum Chordata, sub-phylum Vertebrata. Fish are generally
spindle-shaped, oval in section, and flattened either sideways or dorsal-ventrally. The skin is
covered in protective scales, with some exceptions (lampreys, ocean sunfish). All fins have fins
of some sort, all the size, number, and shape vary. Fish breathe through gills, and only a very
few have actual lungs. Most fish have a special organ known as a swim bladder that prevents
them from sinking, and, in some cases, aids in respiration. The common name "fish" refers to
four different classes, depending on the person classifying them(there are numerous different
ways to classify fish). Bony fish also have special adaptations that allow them to remain
buoyant. A special organ called a swim bladder housed under the bony skeleton is a gas filled
chamber that allows the bony fish to remain floating in the water. Some fish have a connection
between this organ and the digestive tract to allow the extraction of oxygen. Another special
adaptation is the operculum, a flap on each side of the fish that covers the chambers housing
the gills. A bony fish is able to breathe without swimming simply by moving the operculum.
Other hallmarks of these fish are paired fins, many teeth, dermal scales in the skin (in most
species), and numerous vertebrae. Most bony fish are ray-finned fish, meaning that they have
thin, flexible skeletal rays. Lobe-finned fish, the other type of bony fish, have muscular fins
supported by bones. Only one species of lobe-finned fish, the coelacanth, still lives. However, it
was the lobe-finned fish that made possible the colonization of land.
The class Osteichthyes is made up of 26000 species of bony fish. These are all the common fish
and eels found in both salt and/or fresh water. They fertilize their eggs in one of two ways:
externally (the male fertilizes the eggs after they have been laid), or internally. There are
generally two types of eggs: the kind that float (pelagic) or the kind that sink.
There are about 34 orders in two subclasses:
Subclass: Sarcopterygii (fleshy-finned fish)
Crossopterygii (coelacanth)
Ceratodiformes (Australian lungfish)
Lepidosireniformes (South American lungfish)
Subclass: Actinopterygii (ray-finned fish)
Polypteriformes (bichir, redfish)
Acipensiformes (paddlefish, sturgeon)

2. Amiiformes (bowfin, garpike)
Elopiformes (tarpon, tenpounder)
Anguilliformes (eel)
Notacanthiformes (spiny eel)
Clupeiformes (herring, anchovy)
Osteoglossiformes (arapaima)
Mormyriformes (elephant-trunk fish)
Salmoniformes (salmon, trout)
Gonorhynchiformes (milkfish)
Cypriniformes (carp, barbs, loach)
Siluriformes (catfish)
Myctophiformes (lantern fish, Bombay duck)
Percopsiformes (pirate perch)
Batrachoidiformes (toadfish)
Gobiesociformes (clingfish, dragonets)
Lophiiformes (anglerfish)
Gadiformes (cod, pollack)
Atheriniformes (flying fish)
Lampridiformes (opah, ribbonfish)
Beryciformes (squirrelfish)
Zeiformes (John Dory)
Gasterosteiformes (seahorse, stickleback)
Channiformes (snakeshead)

3. Synbranchiformes (swamp eels)
Scorpaeniformes (scorpionfish, gurnard)
Dactylopteriformes (flying gurnard)
Pegasiformes (sea-moth)
Pleuronectiformes (flatfish)
Tetraodontiformes (triggerfish, ocean sunfish, pufferfish)
Perciformes (perch, cichlid, gobies, wrasse, tuna, swordfish, ice fish)
Characteristics of Class Osteichthyes
Characteristics of Class Osteichthyes are given below:
1) Skin with mucus gland. Paired fins made of rays and spines, or lobed fins lacking the rays and
spines.
2) Various types of scales (ctenoid, ganoid, or cycloid).
3) Marine and fresh water species.
4) Gills used for respiration
5) External fertilization. Spawning. Oviparous.
6) No external ears
7) No eye lids.
8) Skeleton made of bone
9) Lateral line
10) Two chambered heart. Operculum covering the gills. Brain with large optic lobes and
cerebellum.
Example: Hippocampus

4. Fossil record Of Osteichthyes
1. Primitive fishes date back to the Cambrian period, about 550 million years ago. These jawless
fishes lived relatively unchanged over the following 100 million years.
2. Bony fishes and cartilaginous fishes (such as sharks and rays) arose from a common ancestor.
3. The Devonian period, about 360 to 400 million years ago, is known as the "Age of Fishes,"
because of the abundance and diversity of fishes that appear during this period.
a. In the Devonian, fishes began to develop jaws and paired fins. All four living classes of
fishes and the three major groups of Osteichthyes were establishedby the mid-Devonian.
b. Many of the groups of fishes that developed during the Devonian are now extinct.
(1) Until 1938, scientists thought that all Crossopterygians were extinct. In 1938,
however, a living member of this group, the coelacanth Latimeria chalumnae was
discovered off the coast of Southeast Africa.
(2) Experts theorize that extinct ancestors of the coelacanth gave rise to
amphibians, which appear in the fossil record at the end of the Devonian.
4. Bony fishes continued to evolve after the Devonian period.
a. Most orders of bony fishes probably evolved during the Triassic period, about 200
million years ago.
b. Today, the Actinopterygians are the dominant vertebrates in the oceans and in
freshwater systems.
c. The most recently evolved orders of bony fishes include the Pleuronectiformes
(flatfishes) and Tetraodontiformes (triggerfishes, pufferfishes, and molas).

5. SOME FISHES OF CLASS OSTEICHTHYES:
Clupisoma garua Chanda nama
Channa orientalis Labeo bata
Channa marulius Cirrhinus reba
Chanda ranga Chaca chaca

6. Botia lohachata Botia dario
Bagarius bagarius Sperata seenghala
Sperata aor Rohtee cotio
Rita rita Puntius ticto

7. Ompok pabda Puntius sarana
Ompok bimaculatus Notopterus notopterus
Notopterus chitala Nandus nandus
Monopterus cuchia Mystus cavasius