Effect of buffered and unbuffered tricaine methanesulfonate (MS-222) at different concentrations on the stress responses of channel catfish, Ictalurus punctatus Rafinesque

The effects of four concentrations (0, 90, 120, and 180 mg/ L) of the anesthetic tricaine methanesulfonate (MS-222) (buffered and unbuffered with sodium bicarbonate) were evaluated on anesthetization efficacy and stress responses of juvenile channel catfish, Ictalurus punctatus Rafinesque. Buffered MS-222 treatments were neutralized with sodium bicarbonate to bring the pH of exposure water to that of rearing water (pH ∼ 7.0). Fish were exposed to MS-222 treatments for 10 minutes after reaching stage 3 anesthetization, or for 10 minutes only for the control treatment (0 mg/L MS-222). Blood was sampled from fish at the end of the 10 minute exposure period and after 30, 60, 120, 240, and 480 minutes recovery in aquaria to measure blood glucose and plasma cortisol and osmolality. With increasing MS-222 concentration, there were significant decreases in pH (7.0 to 5.7) and increases in osmolality (40 to 63 mOsm/kg) in unbuffered water, while osmolality (43 to 69 mOsm/kg), but not pH, were significantly different among the treatments in buffered water. As expected, anesthesia induction time was reduced and recovery time was increased as MS-222 exposure concentration increased. Buffering of exposure water had no effect on anesthetization induction or recovery. Sampling time and MS-222 concentration, but not buffering or pH, had significant effects on the stress responses. Although anesthetization reduced the cortisol response to handling, plasma cortisol concentrations increased with increasing MS-222 concentration regardless of buffering, suggesting an anesthesia effect that was unrelated to MS-222 acidification of exposure water. The blood glucose response also increased with increasing MS-222 concentration; however, glucose concentrations, unlike cortisol, were lowest in handled, non-anesthetized fish, which suggests that stress-related hyperglycemia may not be solely under cortisol control.We determined 90 mg/L MS-222 to be an effective dose for fingerling channel catfish, which provided a moderate rate of anesthesia without significantly exacerbating the cortisol response to handling.