Use of Electroshock for Euthanizing and Immobilizing Adult Spring Chinook Salmon in a Hatchery

Abstract

This study evaluated the use of electroshock as an alternative to traditional techniques for immobilizing and euthanizing hatchery fish. We used a commercially available electroanesthesia unit at the U.S. Fish and Wildlife Service's Carson National Fish Hatchery (Carson, Washington) to euthanize adult spring Chinook salmon Oncorhynchus tshawytscha and to sort and collect gametes of fish at maturation. During euthanization by electroshock, the response of each fish was observed, muscular and vertebral hemorrhaging was quantified, and electrical settings were optimized accordingly. During gamete collection, fish were either electroshocked or exposed to tricaine methanesulfonate (MS-222); hemorrhaging, egg viability, egg size and quantity, and resultant fry quality were examined for each treatment group. Electroshocked fish had a higher likelihood of injury during gamete collection than did fish exposed to MS-222. On average, each electroshocked fish had less than two hemorrhages on both fillets examined. The size of each hemorrhage was less than 0.10% of the fillet surface. Fecundity and egg and fry quality were not affected by either immobilization method. Electroshock was a viable and efficient means of euthanizing adult spring Chinook salmon or sorting the fish and collecting their gametes. However, equipment settings must be optimized based on site-specific (e.g., water conductivity) and species-specific (e.g., fish size and seasonal state of maturation) factors.