 There are over 26 @,@ 000 species of teleosts , in about 40 orders and 448 families . These fish are found in almost every aquatic environment and have developed specializations to feed in a variety of ways as carnivores , herbivores , filter feeders and parasites . The longest teleost is the giant oarfish , reported at 25 ft ( 7 @.@ 6 m ) and more , but this is dwarfed by the extinct Leedsichthys , one individual of which has been estimated to have a length of 91 ft ( 27 @.@ 6 m ) . The heaviest teleost is believed to be the ocean sunfish , with a specimen landed in 2003 having an estimated weight of 2 @.@ 3 long tons ( 2 @.@ 3 metric tons ) , while the smallest fully mature adult is the male anglerfish Photocorynus spiniceps which can measure just 0 @.@ 24 in ( 6 @.@ 2 mm ) , though the female at 2 in ( 50 mm ) is much larger . The stout infantfish is the smallest and lightest adult fish and is in fact the smallest vertebrate in the world ; the females measures 0 @.@ 33 in ( 8 @.@ 4 mm ) and the male just 0 @.@ 28 in ( 7 mm ) . 
