Matthew Duah Osei, Noah Addai-Kumi, Ransford Tawiah, Ruth Acheampong, Douglas Koi Kwaw, Marcus Kofi Oduro and Enoch Appiah
The efficacy of the anaesthetic agent tricaine methanesulfonate (MS-222) was evaluated in the Nile tilapia (Oreochromis niloticus) fingerlings during transportation. MS 222 is an anaesthetic agent that is approved for use in the United States, Canada, the United Kingdom and other European countries. MS-222 is used to suppress the central and peripheral nervous systems of fish to immobilize them for transportation and experimental purposes to avoid mortality and injury.
In the present study, juvenile Nile tilapia of length 7-10 cm were subjected to different concentrations (0-20 mg/L and 100-500 mg/L) of MS-222. O. niloticus subjected to 0 and 20 mg/L (trial experiment) of MS-222 in this study did not reach stage IV anaesthesia (Total loss of equilibrium) within 1 hour, indicating that none of the fish exposed to these concentrations of MS-222 was induced. At 20 mg/L, the buffered MS-222 slowly rendered the fingerlings physiologically inactive (calm) for a prolonged time (> 1 h) and the fish were almost instantly reactivated in untreated water. Sedation time for the fingerlings decreased significantly (p<0.05) with an increase in the anaesthetic concentration (100 – 500 mg/L). MS-222 at 100-500 mg/L successfully induced sedation in Nile tilapia fingerlings, but the optimal concentration was established at 250 mg/L at which sedation time was the same as recovery time. The extremely high concentration of 10,000 mg/L in the trial experiment was lethal; sedation was almost instantaneous (< 5 s) but recovery failed. Lethal doses may be applied to kill fish humanely for post mortem studies in places where animal rights are in force. In general, the higher the concentration, the shorter the sedation time and the longer the recovery time. The required amount of concentration of an anaesthetic agent needed to induce fish varies with the concentration of the anaesthetic agent. The times of sedation and recovery of O. niloticus at various concentrations of MS-222 in this study were found to differ significantly.
Overall, the stress responses vary widely between species, therefore, it is important to screen effective dosages of anaesthetic agents for each cultured species. The definition of efficacy concerning anaesthetics is more or less subjective. The present study showed that MS-222 is efficient in anaesthetizing O. niloticus, an important freshwater fish species in the Tono reservoir
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