Ichthyotoxicity and Rotenone Stability of Derris trifoliata (Leguminosae) Acetone Formulations

The stability of the acetone extract of Derris trifoliata (as a more accessible piscicide for fishpond management) was compared with those of Derris elliptica (Leguminosae) for a duration of seven months with respect to toxicity and rotenone content to Oreochromis niloticus (Cichlidae). Extract formulation of D. elliptica was found to retain its fish toxicity throughout the duration of the experiment without exposure to sunlight while that of D. trifoliata was found to decrease after only about a month. The toxicity of D. trifoliata and D. elliptica formulations were maintained longer, when their extracts were refrigerated at around 9 – 10o C. Chromatographic analysis (HPLC) revealed that although fish toxicity is maintained, rotenone concentration continued to decrease in D. elliptica extracts much faster at conditions where the extracts were exposed to sunlight than if kept in a refrigerator or simply kept inside a room at ambient conditions. However, for the D. trifoliata extract, not much difference was found if it was kept exposed or not to sunlight, as the rotenone concentration in both conditions continued to drop. Placing the extract at 9 – 10o C in a refrigerator prevented this rapid degradation of rotenone. A better way of preventing the toxicity to decrease and the rotenone to degrade was by partitioning the acetone extract between chloroform and water, taking the chloroform extract, evaporating, collecting and reformulating it when needed. This new formulation showed better rotenone stability and consistent toxicity throughout the seven months of experimental observation.