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.

Use of Derris trifoliata (Leguminosae) Root Extracts for Fishpond Management

This study aims to determine whether Derris trifoliata (Leguminosae) locally known as “sila-sila”, can be used in a formulation for fishpond management, compared with the usual commercial source “tubli” (Derris elliptica, Leguminosae). Thus, prior to the formulation of the root extracts, the rotenone content of the roots of Derris trifoliata was determined and compared to two other Derris species, one of which is Derris elliptica. Of the three derris species, D. trifoliata was found to have the lowest rotenone content of 0.019% compared to that of Derris elliptica’s 5.09%. Although D. trifoliata has very low rotenone content, the extract of its root bark and formulation with acetone resulted in 1 L formulations with comparable toxicity as that of D. elliptica or that of a commercial insecticide (illegally used as piscicide). For example, formulations from about 15 kg of root or root bark and 20 L of acetone as extractant produced formulations of about 10 x 1 L for D. trifoliata (rotenone conc. = 0.180 mg•ml-1) and 12 x 1 L for D. elliptica (rotenone conc. = 4.90 mg•ml-1). Both formulations can kill fish such as Oreochromis niloticus (Cichlidae) fingerlings within 30 minutes comparable to a commercial insecticide Telothion 40. The median lethal concentration of the formulation for a 96-hour bioassay against O. niloticus for D. trifoliata was LC50 = 0.03 ppt while for D. elliptica, LC50 = 0.005 ppt. Sensitivity of nine different unwanted fishes near the location of the test fishponds was determined using a D. trifoliata reconstituted formulation. The unwanted fishes appeared more sensitive during summer months when the salinity of water was higher than during the rainy months when the salinity was much lower. Different species of unwanted fishes at different life stages appeared to have different tolerance to the toxicity of the extract. Application of the different formulations previously bioassayed was successful in cleaning several fishponds from unwanted fishes. Cost analysis showed that fish farmers (whose fishponds are located near colonies of D. trifoliata plants) could economize by using extracts of this Derris plant instead of insecticides harmful to the environment or dangerous poisons like sodium cyanide.