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

An ecotechnological approach to control crayfish (Procambarus clarkii) infestation in rice fields of the Lower Mondego River Valley (Central Portugal) has recently been investigated. The application of the biodegradable non-ionic 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-harmful chemical method to mitigate damage caused by crayfish digging activities to rice crops. Therefore, an important requirement regarding the ecological viability of this approach is that populations of non-target species are not significantly affected. A simple mosquitofish (Gambusia holbrooki) population model, in which the relationships with its main food prey were considered, was developed to assess the potential risk to a non-target key species of contaminating the irrigation channels following surfactant application. The model is based on data concerning mosquitofish life cycle and population dynamics, as well as mosquitofish diet and interactions with its main prey species. Quantitative information regarding the acute and sublethal effects of Genapol OXD-080 on mosquitofish and other non-target organisms was obtained from laboratory experiments. Three concentrations of Genapol OXD-080 (0.75, 1 and 2.5 mg/l) were used to simulate a small amount of contamination in irrigation channels. If contamination occurred, the mosquitofish population would tend to decline dramatically, even when submitted to a very 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 populations, and therefore should not be used without taking all precautions to avoid contaminating important biological reservoirs, such as the rice field irrigation channels.