ENERGY DENSITY OF 3 FISHES FROM MINNESOTA WATERS OF LAKE-SUPERIOR

Energy densities of three salmonine prey species in Lake Superior were determined by bomb calorimetry to examine seasonal trends, difference s due to gender and to establish a relation with percent dry weight. T hese results from April through October for 1992 and 1993 were compare d with other studies from the Great Lakes region. Across the 2-year sa mpling period rainbow smelt Osmerus mordax energy density decreased fr om April to June and July then significantly increased into September. Lake herring Coregonus artedii energy density was highest in June, de creased significantly by August and remained stable through October. B loater C. hoyi energy density was lowest in July, then increased in Au gust and early September before decreasing in late September. There we re no significant differences in energy density between males and fema les for rainbow smelt and lake herring collected on the same date acro ss sampling dates. However, bloater energy density was significantly h igher for females than for males on two dates. Energy density estimate s for bloater in Lake Superior were lower than those reported from Lak e Michigan. Energy density values of rainbow smelt and lake herring fe ll within the range reported in Lake Michigan and Lake Ontario (rainbo w smelt), and from two inland lakes in Minnesota and Lake Mendota, Wis consin (bake herring). Percent dry weight was a good predictor of ener gy density (P < 0.001, r(2) = 0.92-0.99) for all three species for bot h years. Percent dry weight vs energy density was significantly differ ent between years for bloater and lake herring, and was significantly different for all three species compared with populations in other lak es in the Great Lakes Region.