Tolerance of Atlantic salmon, Salmo salar L., and ž / rainbow trout, Oncorhynchus mykiss Walbaum , to emamectin benzoate, a new orally administered treatment for sea lice

Ž . Ž . Atlantic salmon weight range 289–484 g and rainbow trout weight range 166–387 g , held in seawater, were fed medicated diets containing graded levels of emamectin benzoate for 7 days. y1 y1 Ž Nominal dose rates were 0, 100, 250 and 500 mg kg body weight day equivalent to 0, 2, 5 . and 10 times recommended dose rate for treatment of sea lice . Fish were observed for a further 7 days to determine the effects of treatment. Calculated actual dose rates, compensated for feed concentrations determined by chemical analysis, feed intake and weight gain during the course of the study, were 0, 70, 173 and 356 mg kg body weight day for Atlantic salmon, and 0, 88, 218 and 413 mg kg body weight day for rainbow trout. No mortality was observed, which could be related to treatment and unequivocal signs of toxicity were recorded only at the highest dose used in these studies. Signs of emamectin benzoate toxicity in both species included lethargy, dark coloration and inappetance. Atlantic salmon also showed loss of coordination. Fish in the high-dose groups exhibiting signs of toxicity showed no evidence of recovery during the 7-day post-treatment period. No pathognomonic signs of emamectin benzoate toxicity were identified ) Corresponding author. Tel.: q44-1586-810287; fax: q44-1586-810295; e-mail: [email protected] 1 Present address: Dr. Hamish Rodger, School of Veterinary Medicine, University of Pennsylvania, 3800 Spruce Street, Philadelphia, PA 19104, USA. 0044-8486r00r$ see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0044-8486 99 00307-5 ( ) W.J. Roy et al.rAquaculture 184 2000 19–29 20 during gross necropsy or histopathological examination. q 2000 Elsevier Science B.V. All rights