Effects of chlorpyrifos on in vitro sex steroid production and thyroid follicular development in adult and larval Lake Sturgeon, Acipenser fulvescens

Chlorpyrifos is a widely used organophosphate pesticide that has previously been shown to enter waterways in biologically relevant concentrations and has the potential to disrupt both thyroid hormone and sex steroid biosynthesis in vertebrates. Because gonadal maturation and larval development in Lake Sturgeon, Acipenser fulvescens, potentially coincide with the application of chlorpyrifos we examined the effects of chlorpyrifos on both thyroid follicular development in larval Lake Sturgeon, and sex hormone synthesis in adult Lake Sturgeon. For the first time, the present study reports steroidogenesis from testicular and ovarian tissue in Lake Sturgeon using an established in vitro bioassay. Furthermore, incubating gonad tissue with 5, 500 or 2000 ng mL−1 chlorpyrifos revealed an inhibitory effect on testosterone synthesis in both testicular (control, 40.29 pg mg−1 tissue wet weight−1 h−1 compared to experimental, 21.84 pg mg−1 tissue wet weight−1 h−1) and ovarian (control, 33.83 pg mg−1 tissue wet weight−1 h−1 compared to experimental, 15.19 pg mg−1 tissue wet weight−1 h−1) tissue. In a second series of experiments, larval Lake Sturgeon were exposed to equivalent concentrations of chlorpyrifos as above for 10 days (d) between hatch and the onset of exogenous feeding. Larvae from each treatment group were raised until 67 days post hatch (dph) and growth rates were compared alongside key indicators of thyroid follicle growth. Chlorpyrifos treatment had no effect on the measured indicators of thyroid follicular development.