Emamectin benzoate: an effective in-feed treatment against the gill parasite Salmincola edwardsii on brook trout

摘要

Emamectin benzoate 0.2% premix (SLICE(TM)) coated onto pellets and fed to brook trout (Salvelinus fontinalis; 700-900 g) resulted in a 40-60% reduction in the mean number of adult female Salmincola edwardsii, whereas controls exhibited a 20% increase in parasite numbers. In each of two lab-based experiments, ca. 40 trout were tagged and the number of adult female parasites on the gills were counted, then the fish were randomly allocated to one of four tanks (300 1, flow through freshwater, 10-12 degreesC). The fish in the two tanks were offered medicated feed (nominal dose 50 mug kg(-1) bw day(-1)) for a 7-day period, the other two tanks were fed a control diet. Finally at either 7 (Experiment 1) or 17-31 days (Experiment 2) after the medicated feed treatment, all fish were euthanised and the number of adult female parasites recounted. In Experiment 1, the mean number of parasites fish(-1) in the treated group decreased from 118 to 49 (p < 0.05), compared to an increase in the control from 109 to 125 (p=0.14). Similarly in Experiment 2, the mean number of parasites fish(-1) decreased significantly in the treated group from 56 to 35 (p < 0.01), compared to an increase from 67 to 82 in the control (p < 0.001). The general health of the fish was improved by the medicated feed in Experiment I as indicated by a significant increase in both mean body weight and condition factor compared to the control. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 25]