Pilot Field Trial to Evaluate SLICE (0.2% Emamectin Benzoate)–Medicated Feed to Reduce a Natural Infestation of Salmincola californiensis in Freshwater-Reared Rainbow Trout

Abstract

Salmincola spp. infestations can adversely affect freshwater-reared salmonids. Control methods tested to date have had limited success; consequently, we conducted a pilot field trial to evaluate SLICE (0.2% emamectin benzoate [EB])–medicated feed to reduce a natural infestation of S. californiensis in freshwater-reared rainbow trout Oncorhynchus mykiss. Before the trial started, 96 of 1,500 rainbow trout broodstock held in a flow-through raceway were impartially captured, sedated, uniquely tagged, and returned to the raceway. Pretreatment S. californiensis infestation prevalence and intensity were 97% and 10.4 ± 7.6 (mean ± SD) adult female parasites per fish, respectively. Treatment was administered at 50 μg EB·kg fish⁻¹·d⁻¹ for 7 d. By the end of the trial (43 d posttreatment), infestation prevalence and intensity had decreased to 32% and 1.6 ± 1.1 adult female parasites per fish, respectively. These results suggest that SLICE-medicated feed can be used to reduce natural infestations of S. californiensis in freshwater-reared rainbow trout.

Received November 15, 2011; accepted January 30, 2012

ACKNOWLEDGMENTS

We thank Merck Animal Health Corp. for supplying SLICE. Cooperation from the staff of the Poudre State Fish Hatchery during tagging the fish and counting S. californiensis was instrumental to completion of the study. Comments from two anonymous reviewers greatly improved the manuscript.