Influence of Prolonged MS-222 Exposure On Survival and Stress of Surgically Implanted Juvenile Salmonids

Many studies have investigated the effects transmitters (acoustic or radio) have on the condition, behavior, and survival of fish; however, few studies have investigated this in relation to anesthetic exposure.  We investigated stress responses to prolonged MS-222 exposure after stage 4 anesthetic induction in surgically implanted juvenile Chinook salmon Oncorhynchus tshawytscha.  Survival, tag loss, plasma cortisol concentration, and blood [Na⁺], [K⁺], [Ca²⁺], and pH were measured immediately following anesthetic exposure and surgical implantation.  Responses were also measured 1, 7, and 14 days post-treatment.  Throughout the study, there were no mortalities or tag loss.  MS-222 was effective at delaying cortisol release, but anesthetic exposure did result in osmotic disturbances, with greater variation in longer MS-222 time exposures.  From day 1 to day 14, [Na⁺], [Ca²⁺], and pH significantly decreased, while cortisol significantly increased in MS-222 exposed fish and was exacerbated by surgical implantation.  There was a significant interaction between MS-222 exposure time and observation day for [Na⁺], [Ca²⁺], [K⁺], and pH; variations were seen in the longer exposure times, although not consistently.  Stress responses suggest that increased exposure to MS-222 can lead to elevated stress in surgically implanted fish.