Fish Facts

  • Fishes are cold-blooded and they can't control their body temperature.
  • Fish can feel pain. They have a good sense of taste, sight and touch. Many fish taste without opening their mouth.
  • Whale shark is the largest fish and they can grow to 50 feet long.
  • Fish like Trigger fish can swim backwards.
  • If gold fish is kept in a dark room it will lose its color.

Classification of Fish:

Fish, the member of the Animalia Kingdom is classified into Phylum Chordata and Vertebrata Subphylum. Fishes poses notochord, tubular nerve chord, paired gills, segmentation of the body parts, post anal tail, ventral heart, and an endoskeleton to be the member of the Chordata. In order to be a vertebrate, it poses backbone. This back bone supports and protects the spinal cord.

All the species of the fish found in the world are classified into the following three groups. They are:

  • Agnatha - jawless fish
  • Chrondrichthyes - cartilaginous fish
  • Osteichthyes - bony fish
    • Ray finned group
    • Lobe finned group

About 50 species of Agnatha fish, 600 species of Chrondrichthyes fish and 30,000 species of Osteichthyes fish are found in the world. Most of the fishes in the bony group belong to the ray finned group. According to the biologist there are about 70 fish orders are found in the world.

Sharks and rays; sturgeon and gars; herring-like fishes; trout and salmon; eels, minnows, suckers, and catfish; flying fish and relatives; cod-like fish; flatfish; seahorses and relatives; mullets, silversides, and barracuda; and mackerels and tunas are the main group of fishes.


Phylum: chordate

Subphylum vertebrata

Agnathan are jawless fish and lack paired fins. They also lack the internal skeleton system. They have a circular tooth mouth (cyclostomic) by which they bore the body of their victim and suck their blood. These are classified in to two major types. They are Hagfish and Lampreys.

Characteristic of Agnatha

  • Jaws are absent
  • Paired fins are absent
  • Bony scales and skin plates were present in the ancient species but are absent in the living species
  • Gill pouches are present. They have seven or more pouches
  • Stomach is absent in the digestive system


Phylum: chordate

Subphylum vertebrata

Fearsome predators and harmless mollusc eaters are the members of the Chrondrichthyes. The member of the cartilaginous fish poses true bone and also poses a skeleton made up of cartilage. Only the teeth of this species and rarely the vertebrae are calcified. Sharks, Skates, and Rays make up the group of chrondrichthyes


Phylum: chordate

Subphylum vertebrata

About 30000 species of bony fish are found in this class. Fishes that belong to this species are spindle shaped, oval in section and flattened. Skins are protected by protective scales. Some fishes of this category have actual lungs to breathe and also have sharp eyesight. These bony fishes have a special gas filled chamber called airbladder housed under the skeleton to allow them to remain buoyant. Another adaptation is operculum, a bone on the sides of the fish to protect the chambers that house the gills.

Bony fish are again classified into ray finned and lobe finned fish. Ray finned fish have thin, flexible skeleton rays. Lobe finned fish have muscular fins supported by bones. Bony fish fertilizes either internally or externally. Two types of eggs are laid by the bony fish. They are the eggs that float and the eggs that sink.

Characteristic of Osteichthyes

  • Have more or less bony skeleton and numerous vertebrae
  • Mucous glands and embedded dermal scales are present in the skin
  • Have paired fins
  • Jaws are present
  • Gill arches support the gills and are protected by the operculum

Lungfish, Eels, Acrp, Lizardfish, Silversides and Salmon form the class of bony fish

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