Diet and habitat characteristics of juvenile stages of the endangered sculpin Cottus reinii were investigated in eight rivers flowing into Lake Hinuma, a brackish water lake in Ibaraki Prefecture, eastern Japan, from April to September 2020. Juvenile C. reinii fed mainly on aquatic insects, such as chironomid, baetid, simuliid and trichopterid larvae, and gammaridean amphipods. A generalized linear mixed model based on occurrence/non-occurrence data in the former with a number of environmental variables at sampling sites in eight rivers in May and June (upstream migration period) and August and September (post-migration) revealed that lower weir height, shallower water depth, lower water temperature, greater current velocity, and greater coverage by submerged vegetation were the most significant determinants of juvenile occurrence.
