With 34,300 described species, fish exhibit greater species diversity than any other group of vertebrates. They can be found in nearly all aquatic environments, from high mountain streams (e.g., char and gudgeon) to the abyssal and even hadal depths of the deepest oceans (e.g., cusk-eels and snailfish), although no species has yet been documented in the deepest 25% of the ocean. įish are abundant in most bodies of water. Fish can acoustically communicate with each other, most often in the context of feeding, aggression or courtship. Most fish are ectothermic ('cold-blooded'), allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers like white shark and tuna can hold a higher core temperature. The first fish with jaws appeared in the Silurian period, after which many (such as sharks) became formidable marine predators rather than just the prey of arthropods. Many fish of the Paleozoic developed external armor that protected them from predators. Fish would continue to evolve through the Paleozoic era, diversifying into a wide variety of forms. Although they lacked a true spine, they possessed notochords which allowed them to be more agile than their invertebrate counterparts. The earliest organisms that can be classified as fish were soft-bodied chordates that first appeared during the Cambrian period.

Around 99% of living fish species are ray-finned fish, belonging to the class Actinopterygii, with over 95% belonging to the teleost subgrouping. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Jawless fish † Armoured fish † Spiny sharks Cartilaginous fish Bony fish Ray-finned fish Lobe-finned fishĬladistically included but traditionally excluded taxaįish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Giant grouper swimming among schools of other fish

Fish feed and grow fish