| ubiquitous |
| ultimate |
| ultimobranchial gland |
| ultra- |
| ultra-abyssal zone |
| ultrahaline |
| ultraplankton |
| umbilical cord |
| umbrella species |
| unavailable nomenclatural act |
| unavailable work |
| uncertainty |
| uncinate |
| unculiferous |
| unculus |
| undershot |
| undersized |
| underslung |
| undifferentiated coastline |
| undulating |
| uni- |
| unicaniculate |
| Unicornfishes |
| unicuspid |
| unidentified |
| uniformitarianism |
| uninomen |
| uninominal name |
| uniserial |
| unisexual |
| unisexual fish |
| unit stock |
| unite |
| united |
| univalve |
| Universal Resource Locator |
| universal trawl |
| Universidade Federal de Pernambuco |
| University Museum of Zoology, Cambridge |
| University Museum, Tokyo |
| University of Alabama |
| University of Alabama, Department of Biology |
| University of Alaska at Juneau |
| University of Alaska Museum |
| University of Alberta |
| University of Arizona Museum |
| University of Arkansas Fayetteville, North Carolina |
| University of British Columbia Fish Museum, Vancouver |
| University of California Fish Museum, Santa Barbara |
| University of Central Florida, Orlando |
| University of Colorado Museum, Colorado |
| University of Connecticut Ichthyology Museum, Connecticut |
| University of Florida |
| University of Georgia Museum of Natural History, Georgia |
| University of Guam |
| University of Guyana, Center for the Study of Biological Diversity |
| University of Kansas Museum of Natural History, Kansas |
| University of Louisville, Kentucky |
| University of Maine, Orono, Maine |
| University of Massachusetts Dartmouth, Massachusetts |
| University of Miami, Rosenstiel School of Marine Science, Miami |
| University of Michigan Museum of Zoology, Michigan |
| University of Mississippi, Mississippi |
| University of Nebraska at Omaha, Nebraska |
| University of Nebraska State Museum, Division of Zoology, Nebraska |
| University of Nevada at Reno, Nevada |
| University of New Orleans Vertebrate Collection, Louisiana |
| University of North Carolina Institute of Marine Sciences, North Carolina |
| University of North Carolina, Charlotte |
| University of Puerto Rico Department of Marine Sciences, Puerto Rico |
| University of Rhode Island, Department of Zoology, Kingston |
| University of Richmond, Virginia |
| University of South Florida, Tampa, Florida |
| University of Southern Mississippi |
| University of Southern Mississippi, Hattiesburg, Mississippi |
| University of Tennessee, Knoxville |
| University of Texas at Arlington, Merriam Museum |
| University of the Ryukyus Museum, Okinawa |
| University of the South Pacific, Fiji |
| University of Tokyo, Department of Zoology, University Museum, Tokyo |
| University of Washington, Seattle |
| University of West Florida Collection, Pensacola, Florida |
| University of Wisconsin at Milwaukee, Wisconsin |
| University of Wisconsin Zoological Museum, Wisconsin |
| University of Wyoming at Laramie, Wyoming |
| univoltine |
| unjustified emendation |
| unpaired fins |
| unsegmented |
| Uo-dango |
| Uo-miso |
| UOG |
| upland |
| upper eyelid |
| upper jaw length |
| upper limb |
| upper origin |
| upper postventral margin |
| Uppsala University, Zoological Museum, Uppsala, Sweden |
| upwelling |
| urea |
| Urochordata |
| urodermal |
| urogenital duct |
| urogenital papilla |
| urogenital region |
| uroneural |
| urophore |
| uropods |
| urosome |
| urostyle |
| usable stock |
| uterine cannibalism |
| uterus |
| Utilitarianism |
| utriculus |
| uvula |
