Effects of chronic clothianidin exposure on rainbow trout (Oncorhynchus mykiss) development

Agricultural run-off is one of the leading sources of environmental pollution in the United States. Insecticides and neonicotinoids have become the most used insecticide class across the world and act as agonists on the nicotinic acetylcholine receptor. Clothianidin is one of the most applied neonicotinoids, yet few studies have investigated its chronic effects on fish. Rainbow trout (Oncorhynchus mykiss) are particularly vulnerable as a nontarget species, as their habitats frequently overlap with areas of agricultural activity. This study exposed developing rainbow trout (15-100 days postfertilization [dpf]) to environmentally relevant concentrations of clothianidin (0, 0.3, 3, 30 μg/L) and analyzed the effects on gross spinal abnormality development, swimming performance, behavior, kidney, and muscle histology. Spinal abnormality was analyzed on mortality of individuals before 72 dpf. At 72 dpf, rainbow trout were randomly selected and euthanized for histological analysis, Swimming performance was conducted on individuals aged 72-93 dpf, followed by behavioral analysis (97-100 dpf). The highest concentration group showed decreased swimming performance and increases in gross spinal abnormalities compared with the control. clothianidin exposure also caused a significant decrease in myofiber size in the lowest and highest concentration group and a significant increase in intermyofiber distance in the two highest concentration groups compared with the control. Chronic clothianidin exposure did not alter behavior nor kidney development. These data show a clear indication that atrophied muscle likely leads to decreases in swimming performance. Because rainbow trout are highly motile species, decreases in swimming performance coupled with increase in spinal abnormalities pose a threat to survivability and migration of this important economic and ecologically relevant species.