Developing Rested Harvest Strategies for Rainbow Trout

Abstract

Harvesting fish for slaughter commonly elicits a generalized stress response, which can negatively affect meat quality and processing efficiency. Sedatives used before or during harvest (i.e., “rested harvest”) can minimize these effects. Use of chemical sedatives is regulated by the U.S. Food and Drug Administration and, unfortunately, none are approved for rested harvest. Electrosedation technology is not currently subject to the same regulatory constraints as chemosedation, but its effectiveness in the context of rested harvest has not been adequately tested. Accordingly, we tested the influence of chemo- and electrosedation rested harvest protocols on Rainbow Trout Oncorhynchus mykiss. Marketable-sized fish (~500 g/fish) were subjected to 3 min of crowding and chasing directly after capture (control) or following treatment with eugenol (10 mg/L) or one of five DC electrosedation protocols. After the challenge, fish were sampled to determine blood chemistry profiles or slaughtered by dewatering (asphyxia) to determine time to mortality and rigor, processing efficiency, and fillet quality. In addition, another group of Rainbow Trout (~520 g/fish) were slaughtered by dewatering or percussion following sedation and the above-described harvest stressors. Overall, results indicated that rested harvest appears to mitigate some aspects of preslaughter stress in Rainbow Trout. Further, rested harvest, including electrosedation-based protocols, appeared to improve some aspects of product quality and may be perceived as a more humane means of slaughter and harvest. The development of rigor mortis was influenced by slaughter method and was delayed by some, but not all, rested harvest protocols. Percussion appears to offer some advantage over dewatering; however, the high postmortem levels of cortisol observed in percussed fish raises some concern. Further research is needed to unequivocally establish the advantages and disadvantages of rested harvest protocols in Rainbow Trout and other cultured fish, but results to date suggest this approach has some merit.

Received March 31, 2016; accepted July 5, 2016 Published online November 18, 2016

ACKNOWLEDGMENTS

The present work would not have been possible without Clear Springs Foods and the company’s commitment of time, expertise, and other resources. In particular, we thank Scott LaPatra, Randy Macmillan, Scott Snyder, and Jeff Quinn for their help in planning and carrying out our experiments, as well as the Snake River Farm and Research Center staff who graciously welcomed us into their facilities and helped along the way. Smith-Root, Inc. was also an essential partner, providing equipment, expertise, logistical support, and help in securing funding. Specifically, Carl Burger, Lee Carstensen, and Martin O’Farrell were instrumental in executing the experiments described herein. We also gratefully acknowledge financial support of this research provided by the U.S. Department of Agriculture, National Institute of Food and Agriculture, Small Business Innovation Research (SBIR) program (award 2013-33610-20876). We thank members of our lab at the Center for Fisheries, Aquaculture, and Aquatic Sciences, Southern Illinois University for their help with project preparation, sample analysis, and data management. We also thank the staff of the Idaho Department of Fish and Game, Eagle Fish Health Lab for storing and shipping samples when needed. Finally, we thank Josh Goldman of Australis, Inc. for his help in conceptualizing an initial version of the project, and Randal Phillips of Aqui-S New Zealand, Ltd. for providing insight regarding eugenol-based rested harvest protocols.