An analysis of the total fish populations in three northern Wisconsin lakes, as revealed by the use of a derris-root treatment, designed to eradicate an undesirable carp population, is presented. The lakes were all bass lakes that had become infested with carp. A concentration of 1.25 pounds of derris root (5 per cent rotenone) was used per acre-foot of water. Preliminary, intensive netting operations were conducted to test the efficiency of 1/2-inch-mesh (stretched measure) fyke nets in estimating fish populations. From 10.4 to 15.6 per cent of the total weight of the fish present and from 6.8 to 31.1 per cent of the total number of individuals were caught. The wide variation in the percentage of individuals taken was due to a difference in species composition in the three lakes.
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