Food of the Bloater, Coregonus hoyi, in Lake Michigan

Stomachs were examined from 1,469 Lake Michigan bloaters, Coregonus \[Leucichthys]\ hoyi, greater than 7 inches long which contained identifiable food. An additional 461 ciscoes less than 7 inches long were incorporated into the study; these latter fish were not positively identified, but most of them undoubtedly were bloaters. The specimens were caught in bottom nets except for 49, all less than 6 inches long, taken in midwater trawls. Lake Michigan bloaters under 7 inches long depend heavily on zooplankton. Those larger than 7 inches feed predominantly on Pontoporeia affinis and Mysis relicta, although fish of the 7.0- to 7.9-inch size range commonly eat zooplankton, especially in shallower water. Generally, Mysis becomes more important, and Pontoporeia less so, as the depth increases and as the season progresses from spring to fall. Incidence of Pontoporeia increases and that of Mysis declines as the fish size increases. Other food items, in decreasing order of importance, are fingernail clams, midges (all stages of development), fish eggs, ostracods, and miscellaneous adult and immature insects other than midges.