Toxic effects of taraxerol extracted from Codiaeum variegatum stem-bark on target vector snail Lymnaea acuminata and non-target fish

The active compound taraxerol (triterpene) extracted from the stem-bark of Codiaeum variegatum Blume (Euphorbiaceae) was administered for 24h or 96h to the freshwater snail Lymnaea (Radix) acuminata Lamarck in order to test its lethality. It was observed that the molluscicidal activity of taraxerol was time as well as dose dependent for the snail at all the exposure periods. There was a significant negative correlation between LC values of taraxerol and exposure period, thus LC50 values decrease from 1.69 mg/L (24h) to 0.74 mg/L (96h) against Lymnaea (Radix) acuminata Lamarck. Toxicity experiments were also carried out on non-target freshwater fish Channa punctatus (Bloch) (Channidae, Ophicephalidae), which shares the habitat with snails, for environmental toxicity, if any. Exposure of sub-lethal (40% and 80% of LC50) doses of taraxerol over 24h caused significant alterations in carbohydrates and nitrogenous metabolism in nervous, hepatopancreas and ovotestis tissues of snail Lymnaea acuminata. Fish Channa punctatus also exposed to sub-lethal doses of taraxerol (40% and 80% of LC50 24h of Lymnaea acuminata) for 96h periods in order to measure potential effects on non-target organisms , also show significant alteration in carbohydrates and nitrogenous metabolism in muscle, liver and gonadal tissues. This study also shows that there is partial recovery in these parameters in both snail and fish after the 7 day of withdrawal of the treatment, which supports the view that it is safe to use plant products as molluscicides for controlling snails in aquatic bodies