BIOEFFICACY AND PHYTOTOXICOLOGICAL ASSESSMENT OF CLITORIA TERNATEA EXTRACT AGAINST THE FRESHWATER FISH CHANNA PUNCTATA

Abstract

Botanical piscicides are regarded as biodegradable alternatives to synthetic chemicals for removing unwanted predatory and weed fishes from nursery ponds before stocking. The present study evaluated the bioefficacy and toxicological effects of the ethanolic leaf extract of Clitoria ternatea L. (Fabaceae) against the freshwater air-breathing snakehead Channa punctata (Bloch). Preliminary phytochemical screening showed alkaloids, flavonoids, saponins, tannins, phenolics, glycosides, terpenoids and proteins in the extract. Static-renewal acute bioassays were run at six concentrations (50–300 mg/L) for 96 h and the median lethal concentration was estimated by probit analysis. Mortality was dose- and time-dependent: the LC50 fell from 224.3 mg/L at 24 h to 133.3 mg/L at 96 h. Exposed fish showed surfacing, erratic swimming, heavy mucus secretion and loss of equilibrium before death. Fish were then exposed for 21 days to two sub-lethal concentrations, 13.3 mg/L (1/10 of the 96 h LC50) and 26.7 mg/L (1/5 of the 96 h LC50). At the higher sub-lethal concentration, liver protein and glycogen fell by 26.1% and 42.0%, blood glucose rose by 54.3%, serum ALT and AST rose by 85.3% and 67.7%, and brain acetylcholinesterase activity fell by 35.9%. Erythrocyte count, haemoglobin and haematocrit declined by 22–25%, while total leucocyte count rose by 39.4%. All sub-lethal changes were significant (P < 0.05) and dose-dependent. The extract can therefore be classed as a moderately active botanical piscicide for C. punctata, and its sub-lethal residues are capable of producing metabolic, hepatic, neural and haematological stress in fish. Field dose optimisation, recovery studies and non-target safety testing are needed before pond-level use.