Anaesthetic potency of MS 222 and neutralized MS 222 as studied in three freshwater fish species

Abstract

1. The effects of several different concentrations of MS 222 and neutralized MS 222 on aquarium water quality and anaeshetic potency were investigated in Cyprinus carpio, Sarotherodon mossambicus and Salmo gairdneri. 2. MS 222 caused a decrease in pH and bicarbonate alkalinity with a corresponding increase in pCO 2 of the aquarium water. Conductivity was also increased. Neutralized MS 222 prevented, apart from an increase in conductivity, such effects. 3. Increasing the concentration of MS 222 in the aquarium water resulted in a decrease in anaesthetic induction times in all three fish species studied. Neutralized MS 222 induced anaesthesia, reduced induction times further and also increased recovery times from anaesthesia. 4. The amount of free MS 222 in the blood of the three fish species studied did not differ significantly from each other per MS 222 concentration employed and showed an increase with increased concentrations of MS 222. With neutralized MS 222 the concentration of free MS 222 in the blood of the three fish species was generally higher. 5. Neutralized MS 222 thus resulted in a deeper, more consistent anaesthesia, thereby indicating a safer, more effective, longer-acting anaesthetic.