Acute and sublethal effects of a non-ionic surfactant, Genapol OXD-080, on mosquitofish Gambusia holbrooki (Girard).

Abstract

Application of the biodegradable non-ionic surfactant Genapol OXD-080, a fatty alcohol polyglycol ester, in rice paddies has been considered as a method to mitigate damage caused by the Louisiana red swamp crayfish, Procambarus clarkii, to rice crops. The damages are a consequence of crayfish digging activities. The acute and sublethal effects of Genapol on a non-target key species were examined to assess the potential risk of contaminating the irrigation channels following its application in the rice paddies. Mosquitofish, Gambusia holbrooki, due to its abundance in irrigation channels, and because it is a predator with an intermediate position in the food chain, was selected as the key non-target species. The LC50 value for Genapol to mosquitofish was 2.9 mg l-1, a value 17.2 times lower than the Genapol concentration needed to decrease crayfish digging activity (50 mg l-1). For sublethal tests, three biological parameters were considered in laboratory experiments with mosquitofish: respiratory metabolism, food (energetic) consumption, and clutch survival. A significant decrease in the resting metabolism of mosquitofish was observed, even when Genapol exposure concentrations were very low (e.g., 0.75 mg l-1). Thus, oxygen consumption rates of mosquitofish are strongly affected by to the presence of this surfactant in water. In contrast, mosquitofish food consumption and clutch survival seemed not to be affected by sub-lethal concentrations of Genapol. Yet, sub-lethal effect concentrations for mosquitofish are so much lower than the concentration necessary to decrease significantly crayfish activity, we conclude that there is a reasonable potential risk of damaging local mosquitofish populations if contamination of the irrigation channels with Genapol occurs.