Catfish

Catfish (order Siluriformes) are a very diverse group of bony fish. Named for their prominent barbels, which resemble a cat's whiskers (though not prominent in all members of this order), catfish range in size and behavior from the heaviest, the Mekong giant catfish from Southeast Asia and the longest, the wels catfish of Eurasia, to detritivores (species that eat dead material on the bottom), and even to a tiny parasitic species commonly called the candiru, Vandellia cirrhosa. There are armour-plated types and also naked types, neither having scales. Despite their common name, not all catfish have prominent barbels; what defines a fish as being in the order Siluriformes are in fact certain features of the skull and swimbladder. Catfish are of considerable commercial importance; many of the larger species are farmed or fished for food. Many of the smaller species, particularly the genus Corydoras, are important in the aquarium hobby.

Piranha

Piranhas belong to the subfamily Serrasalminae, which also includes closely related herbivorous fish including pacus.^[2] Traditionally, only the four genera Pristobrycon, Pygocentrus, Pygopristis and Serrasalmus are considered to be true piranhas, due to their specialized teeth. However, a recent analysis^{[citation needed]} showed that, if the piranha group is to be monophyletic, it should be restricted to Serrasalmus, Pygocentrus and part of Pristobrycon, or expanded to include these taxa plus Pygopristis, Catoprion, and Pristobrycon striolatus. Pygopristis was found to be more closely related to Catoprion than the other three piranha genera.^[2]

The total number of piranha species is unknown and new species continue to be described. In 1988, it was stated^[where?] that fewer than a half of the approximately 60 nominal species of piranhas at the time were valid. More recently (in 2003), one author^[who?] recognized a total of 38 or 39 species, although the validity of some taxa remains questionable.