Egg, Larval and Juvenile Development of Longnose Dace, Rhinichthys cataractae, and River Chub, Nocomis micropogon, with Notes on Their Hybridization

Artificially spawned eggs of longnose dace and naturally spawned eggs of river chub were incubated at 21 ? 3 C through hatching and the larvae reared through the juvenile phase. Development was similar in each species but rates differed. Opercles, mouth, heart and blood circulation developed earlier in longnose dace; fin ray and scale development occurred at a faster rate in river chub. Mean total length of longnose dace at hatching ranged from 4.5 to 5.9 mm and differed significantly between two streams: the smaller larvae hatched from significantly smaller eggs produced by smaller females. No significant differences were found in egg size or mean hatching length in river chub which hatched at a mean total length of 5.9 mm. Larval development was complete at 110 days in longnose dace and 57 days in river chub. Collections in river chub nests contained eggs of longnose dace, river chub, common shiner, creek chub and rosyface shiner in various combinations. Longnose dace and river chub eggs occurred together in each stream sampled and hybrid longnose dace x river chub have been reported from three of the five streams sampled. The use of river chub nests by longnose dace for spawning may be due to a lack of spawning habitat for dace elsewhere in the stream or to a preference for stone nests and may be a primary cause for hybridization between longnose dace and river chub.