Piscicidal Effect of Some Biologically Active Plant Compounds of Alstonia scholaris and Codium variegatum Commonly used in Fresh Water Bodies against Target Fish Mystus mystus

Mortality caused by the aqueous extracts of leaf and stem bark of two plants Alstonia scholaris (family Apocynaceae) and Codium variegatum (family Euphorbiaceae) against freshwater fish Mystus mystus has been investigated in this study.It was observed that the fish may be killed by extracts of leaf and stem bark of these plants.The toxic effect of stem bark and leaf of two plants were time as well as dose dependent.The relationship between exposure durations and LC50 was significantly inverse.LC50 values of stem bark and leaf extracts of Alstonia scholaris and Codium variegatum were decreased from 60.84 mg/l (24 h) to 29.884 mg/l (96 h); 39.766 mg/l (24 h) to 7.93 mg/l (96 h) and 133.75 mg/l (24 h) to 64.79 mg/l (96 h); 115.10 mg/l (24 h) to 31.59 mg/l (96 h), respectively.It has been suggested that these plant products cannot be used directly in freshwater bodies, without their detailed studies on long-term effects on target animal as well their structure activity relationship.