Sharks (lat. Selachii) is a superorder of cartilaginous fish (Chondrichthyes) belonging to the elasmobranch subclass (Elasmobranchii) and has the following distinctive features: elongated body, more or less torpedo-like shape, large heterocercal caudal fin, usually a large number of sharp teeth in each jawSharks are distributed in all the oceans and climatic zones. Most of them live in sea water. Some species, such as roundnose shark, common gray shark and others are capable of living in fresh water, quite far swim in the river. Depth mostly common up to 2000 m, sometimes descending to 3000 meters, and very rarely they were observed below. The largest documented habitat depth belongs to the Portuguese shark — 3700 m.