Effect of Aqueous Leaf Extracts of Lepidagathis alopecuroides on the Behaviours and Mortality of Hybrid Catfish (Heterobranchus bidorsalis ♂ x Clarias gariepinus ♀) Fingerlings

摘要

Lethal renewable bioassay was conducted to evaluate the effect of aqueous extracts of leaves of L. alopecuroides (0.00, 0.5, 1.0, 1.5, 2.0, 2.25 mg/l) on the behaviours and mortality of African catfish hybrid (H. bidorsalis ♂ x C. gariepinus ♀) fingerlings (total length, 7.34±1.78cmSD; mean weight, 2.33±1.96 gSD). Exposed fish were hyperactive, swimming erratically, showed hyperventilation and rapid tail beat with increased mucus secretion on the skin and gills, gulped for air and became listless at he bottom of the aquaria before death occurred. Opercular beat frequency (OBF) and Tail beat frequency (TBF) increased with increase in the concentration of the chemical but decreased with exposure duration. The 96hrsLC₅₀ and safe concentration values were 0.77 and 0.08 mg/l, respectively. The median lethal time (MLT₅₀) for the 0.50 and 2.25 mg/l concentration were 87.72 hrs and 29.72hrs, respectively. The positive linear correlation between mortality, concentration and exposure duration show that mortality was influence by exposure duration and concentration. The low lethal concentration values recorded in this study suggest that L. alopecuroides is highly toxic to catfish hybrid fingerlings.