Acute toxicity studies of the lyophilized aqueous extract of Psychotria microphylla leaf on Clarias gariepinus juveniles

Full Length Research Paper

Acute toxicity studies of the lyophilized aqueous extract of Psychotria microphylla leaf on Clarias gariepinus juveniles

Orji, O. U., Ibiam, U. A. and Aja, P. M.*

Department of Biochemistry, Faculty of Biological Sciences, Ebonyi State University, P.M.B 053, Abakaliki, Ebonyi State, Nigeria.

*Corresponding author. E-mail: ovumte@yahoo.com. Tel: 08039330321.

Accepted 22 May, 2014

Abstract

The piscicidal activity of the lyophilized aqueous extract of Psychotria microphylla leaf on Clarias gariepinus was investigated in a semi-static bioassay to determine the median lethal concentrations (LC₅₀) at 96 h of exposure. Six graded concentrations of 0, 0.27, 0.33, 0.47, 0.67 and 1.33 mg/l of the lyophilized extract were applied to C. gariepinus juveniles (mean weight: 180 g and length: 25 cm) in plastic containers. The 24, 48, 72 and 96 h LC₅₀ values (with 95% confidence limits) estimated by probit analysis were 0.65 (0.57-0.77), 0.53 (0.45-0.65), 0.41 (0.33-0.49) and 0.35 (0.26-0.42) mgl^-1, respectively. During exposure, fish exhibited discolouration, gulping for air, erratic swimming, loss of reflexes, slow opercular movement and ultimately settling at the bottom motionless just before death. The toxicity of the aqueous extract of the plant against C. gariepinus was both time and dose dependent. It is thought that this plant extract or powder will be useful in aquaculture to eradicate predators and competing wild fish from nursery, rearing and stocking ponds prior to the stocking of commercially grown fry and fingerlings of desired species.

Key words: Psychotria microphylla, Clarias gariepinus, toxicity, juveniles, lethal concentration.