Great Basin Naturalist


We compared diet of young-of-year Colorado squawfish (Ptychocheilus lucius), an endangered cyprinid, with diets of other fish < 75 mm total length (TL) collected from backwaters of the Green River between river kilometers 555 and 35 during summer and autumn 1987. Species included native Rhinichthys osculus, Catostomus discobolus, and C. latipinnts, and nonnative Cyprinella lutrensis, Notropis stramineus, Pimephales promelas, Ictalurus punctatus, and Lepomis cyanellus. For each species, diet varied with size and between upper and lower river reaches but not between seasons for fish of similar size. Larval chironomids and ccratopogonids were principal foods of most fishes. Copepods and cladocerans were important in diets of P. lucius < 21 mm TL and L. cyanellus < 31 mm TL. Catostomus discobolus was the only species that ate moderate amounts of algae. Fish (all larvae) were in digestive tracts of only 10 P. lucius (21–73 mm TL), about 1% of P. lucius analyzed. High diet overlap occurred between some size-reach groups of P. lucius and C. lutrensis, R. osculus, C. latipinnis, I. punctatus, and L. cyanellus. Potential for food competition between young-of-year P. lucius and other fishes in backwaters appeared greatest with the very abundant C. lutrensis.