Comparison of the depletion of emamectin benzoate (SLICE®) residues from skeletal muscle and skin of Atlantic salmon (Salmo salar), for multiple dietary dose regimens at 10 °C

The depletion of emamectin B1a in the edible tissues of Atlantic salmon (Salmo salar) was studied at two inclusion rates of emamectin benzoate (EMB; Slice®) in commercially prepared diets. Fish were maintained in tanks supplied by flow-through, temperature-controlled natural seawater at 10.08 ± 0.26 °C. Fish were administered a medicated diet containing a nominal dose rate of EMB at either, 50 μg kg−1 body weight day−1, the recommended manufacturer's dose, or 100 μg kg−1 body weight day−1 for seven consecutive days. Control fish received a non-medicated diet. Two trials were conducted; a single-only dose study where fish were fed 50 μg kg−1 body weight day−1 and a single–double dose comparison study, where fish were fed either 50 μg kg−1 body weight day−1 or 100 μg kg−1 body weight day−1. Laboratory tested EMB concentrations in the diet were 6.82 ± 0.13 mg g−1 of feed for the single-only trial and in the single–double comparison study, 7.6 ± 0.54 mg kg−1 of feed for the single dose and 15.2 ± 1.07 mg kg−1 of feed for the double dose. Individual variability in emamectin B1a of muscle and skin tissues was high and considered related to hierarchal effects of feeding. Emamectin B1a residues were determined in muscle fillet and skin samples at intervals from 1 to 45 days post-feeding in the single-only dose study and 1 to 20 days post-feeding in the single–double dose comparison study. Mean emamectin B1a ranged from 60.5 to 7.3 ng g−1 in the muscle and 199.7 to 28.1 ng g−1 in the skin for the single-only study and in the single–double comparison study, 57.5 to 25.8 ng g−1 in the muscle of the single dose and 96.8 to 45.6 ng g−1 in the muscle of the double dose. Maximum residue levels allowed by Health Canada (CFIA) of 100 ng g−1 and 1000 ng g−1 were never detected in the muscle and skin, respectively, for the recommended dosage of 50 μg kg−1 whereas, 28.6% of fish receiving the double dose of 100 μg kg−1 were observed to have residue levels greater than 100 ng g−1 for muscle, ranging from day 1 through day 20 post-medication.