Comparative Ecology of Two Sympatric Species of Dace (Rhinichthys) in the Fraser River System, British Columbia

Abstract

Age, growth and food habits of leopard dace (Rhinichthys falcatus) in the lower Fraser River are described. Although recently emerged leopard dace and longnose dace (Rhinichthys cataractae) occur together in regions of slow or no current along the river margin, older longnose dace soon begin to occupy regions of higher water velocity. Yearling and older leopard dace remain predominantly in areas of little current. Laboratory experiments in a stream tank demonstrate a strong current preference in longnose dace fry, yearlings and adults. Leopard dace of comparable size show no preference for water current. The swimbladder volume of yearling and adult longnose dace is much lower than that of leopard dace, possibly an adaptation of the former species to occupation of riffle habitat. Temporary coexistence of the two closely related species in the same niche is discussed briefly.