Acute toxicity of water extract of Tephrosia vogelii Hook to species relevant in aquaculture ponds: rotifers, Cyclops, mosquito larvae and fish

Abstract

Rotenone is used to clear ponds of unwanted organisms and trash fish which may predate on fish when the ponds are stocked. Toxicity tests using water extract of the leaves of Tephrosia vogelii Hook, which contains rotenone, were conducted on rotifers (Brachionus species), Cyclops, mosquito larvae (Culex species) and fish (Aphyosemion gardneri nigerianum) in static bioassays. The 48-h LC50s were derived from probit curves using the probit-analysis method, while chisquare was used to test for significant differences between observed mean mortalities and predicted mean mortality values. These showed no significant differences (P > 0.05). The variance ratio of the replicates in each treatment also showed no significant difference (P > 0.05). The 48-h LC50s were found to be 2.89, 1.04, 4.48 and 0.24 mg L)1 for rotifers, Cyclops, mosquito larvae and fish, respectively. The probit mortalities were positively correlated with the log-concentration, except for the rotifers bioassay, which was negative. The fish, A. gardneri nigerianum, was the most sensitive; the mosquito larvae were the least sensitive.