Modeling mosquitofish (Gambusia holbrooki) responses to Genapol OXD-080, anon-ionic surfactant, in rice fields

An ecotechnological approach to control crayfish (Procambarus clarkii) infe station in rice fields of the Lower Mondego River Valley (Central Portugal) has recently been investigated. The application of the biodegradable non-i onic surfactant Genapol OXD-080, a fatty alcohol polyglycol ether, in rice paddies at a given concentration (50 mg/l) has been considered as a non-har mful chemical method to mitigate damage caused by crayfish digging activiti es to rice crops. Therefore, an important requirement regarding the ecologi cal viability of this approach is that populations of non-target species ar e not significantly affected. A simple mosquitofish (Gambusia holbrooki) po pulation model, in which the relationships with its main food prey were con sidered, was developed to assess the potential risk to a non-target key spe cies of contaminating the irrigation channels following surfactant applicat ion. The model is based on data concerning mosquitofish life cycle and popu lation dynamics, as well as mosquitofish diet and interactions with its mai n prey species. Quantitative information regarding the acute and sublethal effects of Genapol OXD-080 on mosquitofish and other non-target organisms w as obtained from laboratory experiments. Three concentrations of Genapol OX D-080 (0.75, 1 and 2.5 mg/l) were used to simulate a small amount of contam ination in irrigation channels. If contamination occurred, the mosquitofish population would tend to decline dramatically, even when submitted to a ve ry small concentration of Genapol OXD-080 (e.g. 0.75 mg/l, 66.7 times lower than the concentration planned to be used in rice paddies). Thus, Genapol OXD-080 could potentially cause vast damage to local mosquitofish populatio ns, and therefore should not be used without taking all precautions to avoi d contaminating important biological reservoirs, such as the rice field irr igation channels. (C) 2001 Elsevier Science B.V. All rights reserved.