Lipid and reproductive characterizations of the grass shrimp, Palaemonets pugio, exposed to endosulfan or methoprene

The toxicity of endosulfan and methoprene was evaluated in the grass shrimp Palaemonetes pugio. Initially, the acute toxicity of these two insecticides was measured. Male shrimp (0.99 μg/L) were nearly twice as sensitive to endosulfan as were females (1.99 μg/L). Methoprene was not acutely toxic to grass shrimp at the highest concentration tested (1.03 mg/L). Responses to sublethal exposure at 200 ng/L endosulfan or 1.03 mg/L methoprene was then assessed. Reproduction was reduced in the endosulfan treatment. The cumulative number of gravid females that appeared during the test was reduced by 26% when compared to controls. Additionally, the rate at which the females became gravid was reduced. Methoprene did not elicit a similar response. Neither endosulfan or methoprene exposure affected embryonic hatching success nor survival 3-d post hatch. However, exposure did significantly increase the time until hatch by roughly 10% in the endosulfan treatment. Lipid analysis revealed significant reductions in total lipids in both the endosulfan and methoprene treatments. Additionally, methoprene treated shrimp exhibited significant reductions in sterol levels and increased triacylglycerol levels. Thus methoprene altered the lipid class profile whereas endosulfan only reduced total lipid levels. The crustacean juvenile hormone methyl farnesoate was quantified for the first time in this species. While the results were variable, tissue residues ranged from 75 to 85 ng/mg wet weight and there were no differences among the three treatments (control, endosulfan or methoprene). The protein contents from embryos were also examined. The major protein (vitellin) was isolated and the molecular weight was estimated to be 380 KDa. Quantification of this protein was compared among three analytical methods: Lowry, HPLC and ELISA. There was very little difference in values among the methods. Values ranged from 250 to 450 μg/mg wet weight. These results begin to identify potential pathways by which EDCs may impact grass shrimp population levels and suggest that lipid alterations may play a role in this response.