The Safety of SLICE (0.2% Emamectin Benzoate) Administered in Feed to Fingerling Rainbow Trout

Abstract

SLICE (0.2% emamectin benzoate [EB]) is an in-feed treatment that has been shown to be effective and safe for controlling infestations of several ectoparasitic crustacean copepods and branchiurans in a variety of seawater- and freshwater-reared fishes. Although the safety of EB (in a pre-SLICE formulation) for use with seawater-reared Rainbow Trout Oncorhynchus mykiss has been demonstrated, the safety of SLICE for freshwater-reared Rainbow Trout has not. Consequently, we conducted a trial to evaluate the safety of SLICE for freshwater-reared Rainbow Trout when administered in feed at a dose of 0 (0×), 50 (1 × the maximum proposed therapeutic dose [1×]), 100 (2×), or 150 (3×) μg of EB·kg of fish body weight (BW)⁻¹·d⁻¹ for 14 d (2 × the proposed 7-d treatment duration). Medicated feed was prepared by top-coating commercially available feed with SLICE. Rainbow Trout fingerlings (mean TL ± SD = 7.4 ± 0.7 cm; mean weight ± SD = 4.4 ± 1.2 g) were stocked into 57-L flow-through tanks at 20 fish/tank. Diets were randomly assigned to four replicate tanks per treatment; fish in four additional, nontrial tanks were fed control diets and were weighed weekly to calculate the proper feeding quantities. Throughout the trial, water quality was maintained within ranges suitable for Rainbow Trout culture, fish were fed the assigned feeds at 4% BW/d divided equally between three feedings, and fish behavior was characterized as normal. Fish in the 0×, 1×, and 2× exposure groups consumed all of the offered feed at least 92% of the time, whereas fish in the 3× exposure group consumed all of the offered feed 75% of the time. No fish died, and gross and microscopic fish health evaluations revealed no chronic toxicity patterns. Based on these results, we conclude that there is an adequate margin of safety associated with administering SLICE-medicated feed to fingerling Rainbow Trout at the proposed therapeutic treatment regimen of 50 μg EB·kg fish BW⁻¹·d⁻¹ for 7 d.

Received March 4, 2013; accepted May 11, 2013

ACKNOWLEDGMENTS

Merck Animal Health supplied the SLICE for the trial and paid for analysis of EB in feed samples. Niccole Wandelear (Aquatic Animal Drug Approval Partnership Program) prepared the medicated feeds and helped to collect data. Beth MacConnell (Headwaters Fish Pathology, LLC) evaluated the histology samples. Jennifer Royston was the independent Quality Assurance Officer. Jesse Trushenski (Southern Illinois University) and Richard Endris (Merck Animal Health) reviewed the manuscript. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USFWS.