Comparison of Electronarcosis and Carbon Dioxide Sedation Effects on Travel Time in Adult Chinook and Coho Salmon

Immobilization of fish during handling is crucial in avoiding injury to fish and is thought to reduce handling stress. Several methods of fish immobilization have been used throughout the history of fisheries management with chemical sedatives being employed most typically. However, most chemical sedatives accumulate in tissues and often food fishes must be held until accumulations degrade to levels safe for human consumption. Historically there have been few options for non-chemical sedation. The use of carbon dioxide (CO₂) as a sedative has been widely-used for decades and does not require a degradation period but has drawbacks. The use of electric “shock”, aimed at immobilization of study fish, is another non-chemical option that does not require degradation time. However, little is known about latent and delayed effects on behavior of migrating adult salmonids treated with electro-immobilization. We compared travel times of adult Chinook and Coho Salmon through a fishway, and to points 12.5 and 28.5 km upstream, after being immobilized with either CO₂ or electronarcosis. Travel times of fish treated with either CO₂ or electronarcosis were similar. Because of the nearly instantaneous induction of and recovery from electronarcosis, we recommend it as an alternative to CO₂ for handling large adult salmonids.