Various fisheries and aquacultural practices such as handling, transportation, tagging and so on stress fish. To minimise the stress, fish should be anaesthetise using agents that is safe, cheap in cost and extraction, effective and readily available and which should induce anaesthesia and recovery within few minutes as compared to synthetic anaesthetics. This study investigated the efficacy of tobacco leaves extract (Nicotiana tabacum) as an anaesthetic agent on Clarias gariepinus juveniles and adults. Ethanolic extracts of the leaves at 50 mg L−1, 100 mg L−1, 150 mg L−1 and 200 mg L−1 were used to anaesthetise juveniles and adults of the fish in order to vary the effects of increasing concentrations on the fish. Least induction time in juveniles was 166.72 ±7.15s recorded in 200 mg L−1, while highest induction time of 476.32 ±3.29s was in 50 mg L−1. In adult, least induction time was 440.99 ±2.42s in 200 mg L−1 concentration, and highest was 916.75 ±6.65s in 50.00 mg L−1. Highest and lowest recovery times in juveniles were 1078.68 ±19.80s and 751.21 ±7.65s in 200 mg L−1 and 50.00 mg L−1 respectively. In adult, least recovery time was 361.83 ±5.14s in 50.00 mg L−1, while 200.00 mg L−1 produced the highest recovery time at 548.45 ±7.78s. 200 mg L−1 concentration of tobacco extract was the effective concentration, as it induces anaesthesia within 3 minutes and recovery within 9 minutes with no mortality. These high induction and recovery times may be due to scalessness and well vascularised skin of the fish and its high body lipid content which make nicotine to diffuse faster in and out of the body. 200.00 mg L−1 ethanolic extracts of tobacco leaves could be used to anaesthetise fish as it is safe, low cost in terms of purchase and extraction, readily available, biodegradable (without residual effect), eco-friendly and efficient. It can serve as an alternative to expensive, toxic, scarce MS-222 or clove oil in fisheries and aquaculture.
