The Potential Application of Hypothermia for Anesthesia in Adult Pacific Salmon

We subjected 190 adult pink salmon Oncorhynchus gorbuscha to water temperatures of −1.5, −3.0, −4.5, and −6.0°C to evaluate the potential of hypothermia for anesthesia. The temperatures were obtained by dissolving salt (NaCl) at concentrations ranging from 25‰ to 90‰ and recirculating the solutions through a thermostatically controlled chiller. The time to each anesthetic stage (sluggishness, loss of movement, and complete anesthesia) declined with decreasing temperature but did not differ significantly between sexes. The most rapid change in response occurred between −1.5°C and −3.0°C. Time to recovery was also influenced by temperature and was directly related to the time to complete anesthesia. In contrast, anesthesia temperature had no affect on egg survival, nor was there a significant difference in survival between the experimental groups and the control (CO2). We conclude that hypothermia is effective for short-term anesthesia of Pacific salmon Oncorhynchus spp. for spawning but note that its application for iteroparous or freshwater stenohaline species may be problematic because of the physiological effects induced by cold shock and exposure to high salinity. Further work will also be needed to determine its utility for large-scale operation.