The Short-Term Effect of Different Anesthetics on Rainbow Trout (Oncorhynchus mykiss) Swimming Ability

This study investigated four anesthetics effects, low volt electroanesthesia (LVEA), carbon dioxide (CO₂), tricaine methanosulfate (MS-222), and eugenol (AQUI-S 20E), on short-term swimming ability of rainbow trout (RBT). These anesthetics have been used in fisheries management, but there is little knowledge regarding the short-term impact on fish. Fish influenced by anesthesia when released may be subject to increased predation, or a disruption in migration and spawning behavior. Fish were swam in step-wise speed increments based on fish body length with five treatment groups (n=30) after immediately recovering. Swimming behavior was measured in number of tires and critical swimming speed (body lengths/sec; U_crit). 7% control, 12% LVEA, 22% CO₂, 29% MS-222, and 31% AQUI-S 20E reached U_crit. Control average U_crit was 4.8 ± 0.3 bl/sec. LVEA average U_crit was 4.8 ± 0.4 bl/sec. CO₂ average U_crit was 3.4 ± 0.4 bl/sec. MS-222 and AQUI-S 20E average U_crit was 3.2 ± 0.89 and 4.3 ± 0.7 bl/sec respectively. LVEA and control fish were observed to have fewer tires (p<0.05) and were less likely to reach U_crit (p<0.001). Based on this study, LVEA had the least impact on swimming behavior of RBT. MS-222 and AQUI-S 20E were observed to have the most impact.