Data collected from rotenone samples of 3 coves before (1959-65) and after (1977) infestation by Eurasian water-milfoil (Myriophyllum spicatum) were compared to document changes in the fish populations. Using the mean of the 3 areas for comparison, both weight and number per hectare increased after water-milfoil infestation. The average weight per individual decreased from 0.02 kg (1959-65) to 0.008 kg (1977). The species were separated into 7 groups. Six of the groups had higher mean numbers per hectare and all groups had higher mean weights per hectare. Multivariate analyses of variance showed that the population structure had changed for numbers and weights per hectare. Ictalurids and yellow perch (Perca flavescens) had the greatest proportionate increases in numbers, whereas largemouth bass (Micropterus salmoides) and white perch (Morone americana) had the greatest proportionate decreases. lctalurids and centrarchids, other than largemouth bass, exhibited the greatest proportionate increases in weights per hectare, while largemouth bass and other fish showed the greatest proportlonate decreases. Numbers of young-of-the-year and older largemouth bass per hectare were not significantly different between pre- and post-water-milfoil samples.
