IVERMECTIN DEPURATION IN ATLANTIC SALMON (SALMO-SALAR)

The depuration of ivermectin (22,23-dihydroavermectin B-1a/B-1b) from Atlantic salmon (Salmo salar) muscle and skin was studied following ni ne weekly oral treatments, at a dose rate of 50.0 mu g/kg of body weig ht per day. Depuration from both tissues followed first-order kinetics with slightly longer retention times being recorded for the skin (t(1 /2) = 188.1 degree days (degrees D)) than for the muscle (t(1/2) = 120 .4 degrees D). Residues of 7.2 +/- 4.7 mu g/kg could be detected in mu scle tissues following 500 degrees D withdrawal, after which they fell below the limit of determination (2.0 mu g/kg). In contrast, ivermect in residues could be detected m skin following 750 degrees D withdrawa l (5.2 +/- 1.5 mu g/kg) but were not detected after 1000 degrees D, In light of these findings, the use of ivermectin as a potential chemoth erapeutant for the control of sea lice infestations of cultured salmon is discussed.