vary greatly in size. The whale shark and basking shark exceed all other fish by a considerable margin in weight and length. Fish are a paraphyletic group that describes aquatic vertebrates while excluding tetrapods, and the bony fish that often represent the group are more closely related to cetaceans such as whales, than to the cartilaginous fish such as sharks and rays. As such, cross group comparisons on this page only serve a colloquial purpose.
The largest known fishes of the now-extinct class Placodermi were Dunkleosteus and Titanichthys. These particular animals may have reached lengths of and are estimated to have weighed 3.6 tons.
The cartilaginous fish are not directly related to the "bony fish," but are sometimes lumped together for simplicity in description. The largest living cartilaginous fish, of the order Orectolobiformes, is the whale shark, of the world's tropical oceans. It is also the largest living animal that is not a cetacean and, like the largest whales, it is a docile creature that filter-feeds on tiny plankton. An average adult species measure long and weigh an average of 9 tonnes. The largest verified specimen was caught in 1949 off Karachi, Pakistan and was long and weighed 21.5 tonnes. Although many are dubious, there are several reports of larger whale sharks, with reliable sources citing unverified specimens of up to 37 tonnes and.
The largest living bony fish is the widely distributed ocean sunfish and southern sunfish, both being members of the order Tetraodontiformes. The record size ocean sunfish crashed into a boat off Bird Island, Australia in 1910 and measured from fin-to-fin, in length and weighed about, while the biggest Mola alexandrini was also coincidentally 2,300 kg in mass and 3.0 m in length, caught off in 1996 and misidentified as a Mola mola. As to length, the longest extant bony fish on earth is the oarfish. Slender and compressed, it averages over long at maturity. A specimen caught in 1885 of in length weighed. The longest known example, which was hit by a steamship, was measured as long, but unverified specimens have been reported up to. Much larger bony fish existed prehistorically, the largest ever known having been Leedsichthys, of the Jurassic period in what is now England. This species is certainly the largest bony fish ever and perhaps the largest non-cetacean marine animal to have ever existed. Estimates of the size of this fish range from and mass from 20 to 50 tons. A maximum size of and 25–30 tons has been deemed to be most realistic.
The largest living lobe-finned fish is the coelacanth. The average weight of the living West Indian Ocean coelacanth,, is, and they can reach up to in length. Specimens can weigh up to. The largest lobe-finned fish of all time was Rhizodus at up to.
