Embryonic Exposure to Thiamethoxam Reduces Survival and Alters Neurobehavior of Fathead Minnows

Thiamethoxam is a commonly used neonicotinoid insecticide that acts as a nicotinic acetylcholine receptor (nAChR) agonist. Although vertebrates are less sensitive to neonicotinoid insecticides than invertebrates, some neonicotinoids have been shown to cause neurobehavioral changes in larval fishes. In the present study, we examine the neurobehavioral toxicity of acute and chronic exposure to environmentally relevant concentrations of thiamethoxam in fathead minnows at two different life stages. Whereas acute exposure of embryos to thiamethoxam does not appear to stimulate spontaneous contractions within 1 min, chronic exposure of embryos to 1.57 µg or more thiamethoxam/L caused increased mortality as well as a subtle increase in spontaneous contraction frequency (SCF), which was negatively correlated with early hatching success. Chronic exposure of embryos to 155 µg thiamethoxam/L impaired predator escape response, and chronic exposure to 0.02-14.61 µg thiamethoxam/L impaired foraging efficiency of some fish. Fathead minnows exposed to thiamethoxam beginning post hatch did not experience changes to measured health or neurobehavioral indicators. Taken together, our findings indicate that embryonic life stages are more sensitive to thiamethoxam exposure than later larval life stages. Because early exposure to thiamethoxam can cause deficits in predatory escape behaviors and may impair foraging success, further study of the potential direct and nondirect impacts of thiamethoxam on wild fish populations is warranted. Environ Toxicol Chem 2022;41:1276-1285. © 2022 SETAC.