Anesthetic effect of eugenol and menthol on handling stress in Macrobrachium rosenbergii

A combination of eugenol and menthol was tested for mitigating handling stress of adult Macrobrachium rosenbergii. Prawns were first exposed to four different doses (100, 200, 400 and 800 µL L− 1) of eugenol and menthol; both individually and in combination. The dose at which induction and recovery time less than 30 min was regarded as the critical dose. It was demonstrated that 200 µL L− 1 dose was sufficient for induction, recovery and significantly (p < 0.05) lower oxygen consumption rate. Further, metabolic responses [glucose, lactate dehydrogenase (LDH), malate dehydrogenase (MDH), alanine amino transferase (ALT) of M. rosenbergii were higher when exposed to 30 min handling stress alone (T1), over (T2) when exposed to stress in the presence of the anesthetic mixture. Lower levels of glycogen and acetylcholine esterase (AchE)] were observed in T1 over T2, indicating secondary metabolic responses to cope up with the stress due to handling. A control (without handling stress and sampling without anesthetic exposure) was maintained to compare the effect of handling stress. In order to ensure its margin of safety, accumulation and clearance of the anesthetic residues were tested from the muscle of M. rosenbergii, which indicated that eugenol and menthol accumulate in tissues of M. rosenbergii. However, 24 h purging protocol cleared the residues completely from the tissues of M. rosenbergii. Overall results indicate that eugenol and menthol based anesthetic formulation is safe and effective for handling of adult M. rosenbergii.