Life History and Ecology of Western Blacknose Dace, Boone County, Iowa, 1963-1964

A life history and ecology study of the western blacknose dace, Rhinichthys atratulus meleagris (Agassiz), was made on Elkhorn and Pease creeks, Boone County, Iowa. Total length equals 1.23 standard length; live length equals 1.03 preserved length; and live weight equals 0.90 preserved weight. Dace reached maturity at age II. Spawning occurred from early May through July over gravel. Number of eggs increased with length of females. Scale formation proceeded forward from the caudal peduncle at 16-20 mm standard length. Scale growth was not directly proportional to body growth. Annuli formed between March and May. Fish which lacked scales until spring of the second year lacked a first annulus. Fastest growth occurred during May, June and July for age I and II dace. Age 0 fish reach an average of 24-27 mm in length during their first year. Age I fish reach 49-50 mm. Few fish reach age III. Length-weight relationships differed significantly between sexes and populations. Diptera larvae were the only consistently utilized food item. Predation by creek chubs occurred. Up to 100 nematodes of the genus Rhabdochona per dace were found with no apparent harmful effects. Although dace overwintered in pools of both streams, some moved into the Des Moines River. During summer, dace concentrated in cool headwaters