Fish beginning with U
- Uaru amphiacanthoides is a species of fish from the family Cichlidae native to South America
- Uaru fernandezyepezi is a species of fish from the family Cichlidae native to South America.
- Umbrella cichlid , also known as Umbrella Apisto and Yellow Dwarf Cichlid, is a species of fish in the genus Apistogramma.
- The umbrella conger, Gnathophis umbrellabius, is a conger of the family Congridae, found on soft bottoms of the continental shelf of the southwest Pacific Ocean.
- The Umpqua Chub is a species of ray-finned fish in the Cyprinidae family.
- In New Zealand, this trevally is known by the Māori as araara, and is generally confined to waters north of Cook Strait, although it sometimes reaches as far south as Otago in the summer.
Undulate painted ray
- The Undulate ray features a round disc shaped head, and contains small prickles used for protection.
- The undulated moray, Gymnothorax undulatus, is a moray eel of the family Muraenidae, found in the Indo-Pacific oceans and the eastern Central Pacific at depths down to 30 m.
- The unicorn crestfish or unicornfish, Eumecichthys fiski, is a very rare, little-known species of crestfish in the family Lophotidae, and the only member of its genus.
- The unicorn leatherjacket, Aluterus monoceros, is a filefish of the family Monacanthidae, found around the world in subtropical oceans between latitudes 43° N and 35° S, at depths down to 50 m.
- The upland bully, Gobiomorphus breviceps, is a sleeper of the genus Gobiomorphus, found in most rivers and lakes in the South Island and the southern half of the North Island of New Zealand.
Upper Zambezi yellowfish
- The Zambezi yellowfish, Labeobarbus codringtonii, is commonly found throughout the Zambezi and Okavango Rivers in Southern Africa.
- The New Zealand urchin clingfish, Dellichthys morelandi, is a clingfish, the only species in the genus Diplocrepis.
- The Chesterfield Island stingaree or Deforge's stingaree, Urolophus deforgesi, is a species of fish in the Urolophidae family.
- The New Caledonian stingaree, Urolophus neocaledoniensis, is a species of fish in the Urolophidae family.
- The butterfly stingaree, Urolophus papilio, is a species of fish in the Urolophidae family.
- The Scale-eye plaice, Acanthopsetta nadeshnyi, is a flatfish of the family Pleuronectidae.
- Ursinoscorpaenopsis kitai is a marine fish that is the sole species of the genus Ursinoscorpaenopsis.
- This chub generally follows the cyprinid body plan.
Utah Lake sculpin
- The Utah Lake sculpin was a benthic species , invertebrates constituting its major source of food.
- This is a large fish that can grow up to 65 cm in length.