The potential application of hypothermia for anesthesia in adult Pacific salmon

We subjected 190 adult pink salmon Oncorhynchus gorbuscha to water temperat ures of -1.5, -3.0, -4.5, and -6.0 degrees C to evaluate the potential of h ypothermia for anesthesia. The temperatures were obtained by dissolving sal t (NaCl) at concentrations ranging from 25 parts per thousand to 90 parts p er thousand and recirculating the solutions through a thermostatically cont rolled chiller. The time to each anesthetic stage (sluggishness, loss of mo vement, and complete anesthesia) declined with decreasing temperature but d id not differ significantly between sexes. The most rapid change in respons e occurred between -1.5 degrees C and -3.0 degrees C. Time to recovery was also influenced by temperature and was directly related to the time to comp lete anesthesia. In contrast, anesthesia temperature had no affect on egg s urvival, nor was there a significant difference in survival between the exp erimental groups and the control (CO,). We conclude that hypothermia is eff ective for short-term anesthesia of Pacific salmon Oncorhynchus spp. for sp awning but note that its application for iteroparous or freshwater stenohal ine species may be problematic because of the physiological effects induced by cold shock and exposure to high salinity. Further work will also be nee ded to determine its utility for large-scale operation.