Seasonal Changes in Food Consumption and Energy Content of Smelt (Osmerus mordax) in Lake Michigan

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Abstract
Seasonal changes in weight of stomach contents and energy content of smelt (Osmerus mordax) in Lake Michigan were examined. Dry weight of stomach contents averaged over a 24‐h period reached a maximum of 0.8% dry body weight during June and decreased to 0.2% during February. Smelt collected during their spawning run were not feeding. Bodies of smelt were divided into carcass, gut, and gonad compartments. Calorific equivalent of the carcass was highest during August when it equalled 5.69 kcal/g dry weight. Calorific equivalent of the gut compartment was highest during October when it equalled approximately 8.7 kcal/g dry weight for both sexes. Smelt utilized energy stores for overwintering and gonad maturation. Calorific equivalents and dry weights of the gut compartment decreased during the October‐February interval whereas gonads increased in energy content. Calorific equivalents for whole smelt ranged from 5.51 kcal/g dry weight during May to 6.11 in October, averaging 5.79 kcal/g dry weight throughout the study.