Piscicidal and Prophylaxis Potentials of Neem (Azadirachta indica L) Extract in Yolk Fry of African Catfish, (Clarias gariepinus)

Abstract

The study aimed to investigate the lethal range and suitable concentration of Neem leaf extract for prophylaxis use in early life stage of African catfish (Clarias gariepinus) by discovering safe dosage, capable of ensuring improved fry survival in the presence of virulent microbial pathogens. Powdered Neem leaf weight 465.00±0.50 g was soaked in ethanol for 72 hours using standard laboratory procedure for metabolite extraction. Extract was freeze-dried through sublimation process. Freeze-dried extracts were characterised for presence and quantity (mg/g) of 12 antimicrobial related metabolites. 100 each of day-old yolk-fry Clarias gariepinus were immersed in each of 0 mg/L, 5 mg/L, 10 mg/L, 15 mg/L, 20 mg/L, 25 mg/L, 30 mg/L, 35 mg/L, 40 mg/L, 45 mg/L, and 50 mg/L freeze-dried extracts, and in each of pre-LC50 Neem concentrations plus 1 x 10-4 Aeromonas hydrophila (ATCC 19750) inoculum in 24 hours; to respectively determine toxicity range (LC50 and LC100) and survival during prophylaxis. Neem leaf yielded 2.94±0.55% freeze-dried extracts. Qualitatively, 58.33% of tested phytochemicals/metabolites were negative, while Saponin, Tannin, Alkaloid, Flavonoid, and Phenol, representing 41.66%tests were positive. Metabolites’ quantity ranged 3.13±0.13mg/g(Phenol) - 14.97±0.15 mg/g(Tannin). Fry in 0-15 mg/L extract did not reach LC50 in 24 hours. LC50 occurred in 20-35 mg/L at 21-23 hours and 40-50 mg/L at 17-18 hours, LC100 occurred in 40-50 mg/L at 19-23  hour. 0%neem+fry had 100.0±0.0% survival in 24 hours. Survival ranged 0.0±0.0 (16-24 hours) - 100.0±0.0%(4-8hours) in 0neem+Fry+Aeromonas; 0.0±0.0(20-24hours) – 100.0±0.0 (4-8 hours) in 5 mg/L neem+Fry+Aeromonas; 0.0±0.0 (20-24 hours) – 100.0±0.0 (4-8 hours) in 10 mg/L neem+Fry+Aeromonas and 30.0±5.5 (24 hours) - 100.0±0.0 (4-8 hours) in 15 mg/L neem+Fry+Aeromonas. Neem extract contain antimicrobial related metabolites, which is toxic to at least half C. gariepinus yolk fry population at >15mg/L concentrations. Fry survival in virulent A. hydrophila laden rearing medium was slightly improved at 15mg/L concentration.