Assessing the combined effects of bifenthrin and temperature on early life stage sturgeon

Temperature can alter contaminant toxicity in aquatic ectotherms, yet thermal context is rarely incorporated explicitly in pesticide risk assessments. Early life stages of cold-water fishes are particularly sensitive to such interactions, as temperature governs metabolic rate, developmental timing, and physiological tolerance to chemical stress. Here, we examined how bifenthrin interacts with water temperature to exert sublethal effects on larval Green (Acipenser medirostris) and White Sturgeon (Acipenser transmontanus). Larvae (3 day-post-hatch) were exposed for 96 h to 0, 10, 100, or 500 ng/L bifenthrin (nominal concentrations) at 12, 15, or 18°C, followed by a 28-day recovery period; exposure concentrations were analytically verified and presented along with nominal treatment categories. Acute mortality was low (<1% on average), whereas deformity and post-exposure survival showed endpoint- and species-specific temperature dependence. Green Sturgeon showed reduced survival and higher deformity at cooler temperatures, with mean deformity reaching 13.10% ± 2.48% across treatments, whereas White Sturgeon exhibited reduced survival at 18°C but low deformity overall (0.29% ± 0.16%). Temperature also modulated bifenthrin effects on post-exposure survival and growth in a species-specific manner, including enhanced survival in Green Sturgeon at the higher nominal exposure treatments under 12 and 15°C, but weaker and inconsistent responses in White Sturgeon. Elevated temperatures promoted growth in both species, although bifenthrin effects varied with temperature and species. High bifenthrin exposure (nominally 500 ng/L) was associated with behavioral changes in both species, and locomotor reduction was most evident in White Sturgeon, where total distance moved decreased by 123 ± 32 cm relative to controls across temperatures. Acetylcholinesterase activity increased in several warmer and higher-exposure contexts, but this response varied by species, temperature, and exposure concentration. Overall, these results indicate that thermal context can modify bifenthrin responses in early life-stage sturgeon, supporting the incorporation of temperature as a complementary factor in ecological risk assessment under current and future climate conditions.