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

Application of the biodegradable non-ionic surfactant Genapol OXD-080, a fa tty alcohol polyglycol ester, in rice paddies has been considered as a meth od to mitigate damage caused by the Louisiana red swamp crayfish, Procambar us clarkii, to rice crops. The damages are a consequence of crayfish diggin g activities. The acute and sublethal effects of Genapol on a non-target ke y species were examined to assess the potential risk of contaminating the i rrigation channels following its application in the rice paddies. Mosquitof ish, Gambusia holbrooki, due to its abundance in irrigation channels, and b ecause it is a predator with an intermediate position in the food chain, wa s selected as the key non-target species. The LC50 value for Genapol to mos quitofish was 2.9 mg l(-1), a value 17.2 times lower than the Genapol conce ntration needed to decrease crayfish digging activity (50 mg l(-1)). For su blethal tests, three biological parameters were considered in laboratory ex periments with mosquitofish: respiratory metabolism, food (energetic) consu mption, and clutch survival. A significant decrease in the resting metaboli sm of mosquitofish was observed, even when Genapol exposure concentrations were very low (e.g., 0.75 mg l(-1)). Thus, oxygen consumption rates of mosq uitofish are strongly affected by to the presence of this surfactant in wat er. In contrast, mosquitofish food consumption and clutch survival seemed n ot to be affected by sub-lethal concentrations of Genapol. Yet, sub-lethal effect concentrations for mosquitofish are so much lower than the concentra tion necessary to decrease significantly crayfish activity, we conclude tha t there is a reasonable potential risk of damaging local mosquitofish popul ations if contamination of the irrigation channels with Genapol occurs.