Slimy sculpin Cottus cognatus are being reintroduced into coldwater streams in southeastern Minnesota to restore native biotic diversity and provide forage for large trout, but success has been variable. We examined slimy sculpin diets and prey consumption in a series of field and laboratory experiments to assess the potential role of invertebrate prey in affecting reintroduction success. Sculpin consumed 35 different types of prey in the field, but frequency of occurrence was highest and preferences (Ivlev's selectivity index) strongest for Diptera larvae and Amphipoda. Benthic samples indicated that preferred prey items were abundant in most streams. In 24-h feeding experiments, sculpin typically consumed 5 to 15 prey/day, and exhibited selective feeding for Amphipoda (Gammarus), Isopoda (Asellus), and Ephemeroptera (Baetis) while rejecting Trichoptera (Brachycentrus) and Gastropoda (Physella). Sculpin are euryphagous and flexible to varying prey availability in different streams, demonstrating both mixed diets and multiple prey preferences that allow fish to maximize their consumption when confronted with differing prey assemblages. Our data indicate that preferred prey taxa are not limiting and that lack of suitable prey is not a factor in the limited success of sculpin reintroductions in some streams.
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Vol. 168 • No. 1