Variation in Body Form, Taste Buds, and Brain Patterns of the Sicklefin Chub, Macrhybopsis meeki, in the Missouri River and Lower Yellowstone River, USA

Abstract

ABSTRACT The sicklefin chub (Macrhybopsis meeki) is a large river, turbid water, small-bodied fish whose range in the Missouri River system decreased following river channelization and construction of mainstem impoundments. We examined selected phenotypic traits that might be expected to vary in response to the increased velocity in the channelized, lower river and turbidity reduction in the upper river. Sicklefin chub body morphology differed among river areas with chubs in the higher velocity channelized area appearing more hydrodynamically streamlined with longer heads and shorter caudal regions. Sicklefin chubs in the more turbid waters had the highest numbers of compound taste buds on the pectoral and pelvic fins and the shortest optic brain lobes, whereas in the clearest waters chubs had the fewest taste buds and shortest olfactory brain lobes. This indicates that sicklefin chubs in the Missouri River system are responding to increased water clarity by reducing their dependency on phenotypic traits that promote food detection with senses of taste and smell. However, optic brain lobes were not longest in the clearest waters suggesting that chubs have not concomittently developed traits associated with visual senses. Sicklefin chubs may still be adapting to river modifications.