The effects of chemical pesticides may be lethal (acute) or sub-lethal (chronic) and can vary depending on species. However, the majority of ecotoxicological studies have focused on lethal effects and few selected model organisms, neglecting effects on commercially and ecologically important non-target organisms as well as sub-lethal effects. The objective of this study was to investigate the lethal and sub-lethal effects of the insecticide fipronil on juvenile White shrimp Litopenaeus setiferus in a 44-day laboratory experiment. Six different fipronil concentrations including the control (0.0, 0.005, 0.01, 0.1, 1.0, and 3.0 µg/L) have been used in this study. These concentrations were selected based on those found in the environment previously according to the published literature, in addition to one concentration below the chronic level of the U.S. EPA aquatic life benchmark for invertebrates.
Results/Conclusions
Results showed that even at lower concentrations of fipronil, sub-lethal effects have been observed. Although, almost no difference in survivorship was observed among low concentration treatments, the percentage of weight gain differed significantly between the control (51.62 ± 2.29 g) and all treatments except treatment 0.005 µg/L which showed % weight gain of (41.21 ± 5.25 g) at the end of the experiment. The inter-moulting interval of the control (13.6 days) was significantly different from that under the three highest concentrations: 0.1 µg/L (16.3 days), 1.0 µg/L (17.7 days), and 3.0 µg/L (20 days). Behavioral changes were noticed at all treatments even in the lowest concentration (0.005 µg/L). The most notable changes were reduced speed, uncoordinated swimming, and reduced food consumption. Body chemical compositions were significantly different under fipronil exposures and were in a concentration-dependent manner, where the increase of fipronil concentration in treatments has led to reduced lipid, increased ash, and reduced protein content. Therefore, results of this study suggest that using fipronil near estuaries may cause serious sub-lethal effects on white shrimp even below the U.S. EPA benchmark concentration of this widely used insecticide.