The efficacy of MS-222 as anaesthetic agent in four freshwater aquarium fish species

The efficacy of anaesthetic tricaine methanesulfonate (MS-222) was evaluated in four freshwater aquarium fish species, Zebrafish (Danio rerio), Guppy (Poecilia reticulata), Discu (Symphysodon discus) and Green swordtail (Xiphophorus helleri). The correct dose of anaesthetic should induce the plane 4 of anaesthesia in less than 180s, recovery in less than 300s and must survive when exposed during 30min to anaesthetic. Fishes were exposed to six concentrations of anaesthetic (75, 100, 125, 150, 200 and 250mgL(-1)) and the time of fish reaching plane 4 of anaesthesia, post exposure recovery, and the percentage of survival when fish were subject to 30min in the anaesthetic were recorded. The optimal doses varied according to the species: D.rerio - 75, 100 and 125mgL(-1), P.reticulata - 125, 150 and 200mgL(-1), S.discus - 75 and 100mgL(-1) and X.helleri - 125 and 150mgL(-1). The induction time generally decreased significantly with increasing concentration of MS-222 for all of the species evaluated. The recovery time had a tendency to increase with the increase of the MS-222 concentration for D.rerio, P.reticulata and S.discus. On the other hand, X.helleri recovery time decreased with the increase of MS-222 concentration. MS-222 proved to be effective in anaesthesia for all the freshwater ornamental species studied. The main results clearly show that the optimal dose to anesthetize is fish species dependent and it is completely wrong to extrapolate optimal anaesthetic concentrations between different species.