Jornal de Pesquisa e Desenvolvimento em Aquicultura

Abstrato

Toxicity of Rotenone -Yielding Plant Extracts on Fish Fry and Selected Predatory Aquatic Organisms

IA Adebayo and BJ Akin- Obasola

Fish fry raised directly in earthen ponds grow faster and healthier but often threatened by a wide range of predatory aquatic organisms which lead to a decline in population at harvest. This study examined the toxicity of rotenone-yielding plant root extracts of Tephrosia bractiolata and Lonchocarpus sericeus on four predatory aquatic organisms namely: Water tigers (W_t), Tadpoles (T_p), young Crabs (Y_c) and Nymph stage of Dragon fly (N_d). Using the 96 hours bioassay test to determine acute toxicity for each plant extract, the lethal concentrations (LC₅₀) for T. bractiolata and L. sericeus were 7 g and 25 g/70L of water respectively for the test organisms. The aquatic organisms were subjected to four test concentrations (0, 6, 8 and 10 g/70L) for T. bractiolata and (0, 20, 30 and 35 g/70L) for L. sericeus respectively in three replicates. Residual effect of the rotenone extract on a week old fry of Clarias gariepinus as non -target organism was determined a week after termination of the first experiment. Results indicated that T. bractiolata at lower dose (≤ 10 g/70L) was more toxic to the predatory organisms compared to L. sericeus (≤35 g/70L). As concentrations of root extract increased, water quality parameters such as Dissolved Oxygen (DO), pH and turbidity (transparency) were negatively affected. There was no mortality of fish fry at different doses (6-10 g/70L) of T. bractiolata after a week of termination of experiment, while mortality of fish fry was recorded at higher doses (30 -35 g/70L) of L. sericeus, after a week termination of experiment, showing longer residual effect of L. sericeus on fish. In combating aquatic predators in nursery ponds, T. bractiolata has higher potency in killing predators at lower doses compared to L. sericeus with both plant extracts having minimal residual effect on fish and water quality parameters.