Abstract:A wide variety of compounds were used to anaesthetize fish in fisheries research, fisheries management, aquaculture and fish health. Among of them, tricaine mesilate ( MS-222) is one of the anaesthetics widely used in the world for it's safety and high effectiveness. In China, little published information was found on the use of MS 222 in marine fish. In this study, immersion anaesthesia was utilized to investigate the recovery time, recovery rate and survival rate in 24 h of flounder Paralichthys olivaceus after being anaesthetized with different concentrations of MS 222 at the temperature of 13-14 ℃; and the effect of long time immersion anaesthesia in 60 mg/L MS-222 on the recovery rate and survival rate after being transferred from water into air were studied. The results showed that the lowest effective concentration to anaesthetize the flounder was at 50 mg/L. The time to achieve anaesthesia was shortened from 288 s to 50 s and the time to recovery was extended from 94 s to 106 s when the concentration of MS-222 was increased from 50 mg/L to 200 mg/L. Three concentrations of MS-222 including 60 mg/L, 100 mg/L and 200 mg/L were used for long time immersion anaesthesia respectively to evaluate the recovery time, recovery rate and survival rate in 24 h, the results showed that the recovery time in the three groups were prolonged along with the increasing of immersion time, but the longest immersion time to achieve 100 percent recovery rate were 64 min, 32 min and 32 min respectively. Also the time for enduring air exposure was tested after the flounder was exposed in 60 mg/L MS 222, and it was found that their ability to endure air exposure was better than the control. Recovery time showed great difference between individuals and the survival rate in 24h after anaesthesia was 100% once the flounder was recovered. These results indicated that the ideal concentration of MS-222 is 60 mg/L, the time to keep the flounder in MS 222 and the exposed time to air is less than 64 s and 60 min respectively at this concentration.
