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

Abstract

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.