Abstract

The increasing use of plant-derived toxicants in fisheries management and aquaculture has necessitated the evaluation of their effects on non-target aquatic organisms. This study investigated the acute toxicity of leaf extracts of Datura metel, Rauvolfia vomitoria, and Pentodon pentandrus on Tilapia guineensis under controlled laboratory conditions. Tilapia guineensis was obtained from Sombreiro River and leaf extract were obtained using standard procedures. Fish were exposed to varying concentrations (0, 0.25, 0.5, and 0.75 ml/l) of each plant extract and mortality was monitored at specific time intervals over a 24-hour exposure period. Results showed that no mortality occurred in the control groups throughout the experimental period and exposure to Datura metel produced no mortality at any concentration tested. In contrast, both Rauvolfia vomitoria and Pentodon pentandrous  extracts caused significant mortality that increased with concentration and exposure time. For Rauvolfia vomitoria, mortality commenced between 20 and 40 minutes of exposure, with higher concentrations producing earlier deaths. At 0.75ml/l, mortality was observed within 20 minutes, while lower concentrations required longer exposure periods before lethal effects occurred. Pentodon pentandrous exhibited the highest toxicity among the extracts tested. Mortality occurred as early as 20 minutes at concentrations of 0.5 and 0.75 ml/l, and the highest concentration resulted in the greatest number of deaths within the shortest time. No additional mortality was recorded after the first hour of exposure for either extract. The result shows differences in piscicidal activities, with Pentodon pentandrous showing strongest toxic effect, followed by Rauvolfia vomitoria, while Datura metel was non-toxic at the concentrations evaluated. Caution should be exercised in the use of Pentodon pentandrous and Rauvolfia vomitoria in aquatic environments due to their significant toxic effects on fish.