Toxicity of aqueous bark extract of the tree Balanites aegyptiaca on the fish Oreochromis niloticus.

The toxicity of an aqueous extract of Balanites aegyptiaca on Oreochromis niloticus was investigated. Fry of the fish were exposed to acute and sublethal concentrations of the extract in 96-h and 56-d static bioassays, respectively. Susceptibility of the extract on freshwater snail, Biomphalaria pfeifferi, was tested. The LC50 of the lethal concentrations of the extract on the fish and the snails were 1.12 mg/l-1 and 2.0 mg/l-1 respectively, while the effects of the sublethal concentrations on the growth rate and haematocrit percentage of the fish were determined. Signs of toxicosis such as air gulping, reduction in tailfin beating rate and overturning were observed in the fish before death occurred. The toxicant also reduced the growth rate and haematocrit percentage of the fish. The mode of action of the toxicant seems to be haemolytic or an impairment of osmoregulation in the blood leading to an over-dilution of the blood.