Behavioral Changes in Japanese Killifish （Oryzias latipes） Following Exposure to Neonicotinoid Pesticides

抄録

Neonicotinoid insecticides （NEOs） are widely used in many agricultural products. However, it has been pointed out that it may flow into rivers, lakes, and coastal areas and affect organisms inhabiting those environments. In this study, the effects of exposure to NEOs at concentrations and exposure periods observed in rivers, waterways and agricultural drainage channels around rice paddies, where Japanese killifish (Oryzias latipes) inhabit, on their anxiety behavior were assessed by light/dark preference tests. We also examined whether or not the anxiety behavior recovered when reared in clean water after exposure to NEOs. Japanese killifish were divided into seven groups of seven males and females each as follows and reared for one week: pesticide-free （Control）, thiamethoxam （THM） exposure; 10 and 200 μg/L, dinotefuran （DIN） exposure; 6 and 120 μg/L, fipronil （FIP） exposure; 1 and 20 μg/L. Light/dark preference tests were conducted immediately before exposure, one day and one week after exposure to measure the percentage of time spent on a black background （Choice index） and the number of times the fish moved between the black and white demarcation line. After the oneweek exposure test, the Japanese killifish were again subjected to the light/dark preference test after two weeks in clean water to determine any behavioral changes. Before pesticide exposure, Japanese killifish spent most of the time in the dark, but one and seven days after exposure to low and high concentrations of THM and DIN, their dark selectivity was significantly lower than that of the control group. Similar changes were also observed in individuals exposed to FIPs. Furthermore, when the killifish were returned to clean water seven days after exposure and kept for at least two weeks, dark selectivity increased (recovered) again in the FIP-exposed group, whereas dark selectivity did not recover in both sexes in the groups exposed to THMs and DINs. In other words, the effects of NEOs exposure are irreversible or long-lasting, and once exposed, even if the animals return to clean water afterwards, the effects will continue for a long period of time for aquatic organisms, and there is concern about the effects on the ecosystem.