Sex-specific Cognitive Effects of Environmentally Relevant Microplastic Exposure in the Western Mosquitofish

Abstract Microplastics (MPs) are pervasive aquatic pollutants, yet their behavioral and cognitive effects in wild fish, particularly across sexes and environmentally relevant exposures, remain poorly understood. This study examines the effects of polyethylene terephthalate (PET) microfiber exposure on cognition, behavior, and body condition in male and female western mosquitofish ( Gambusia affinis ). Individuals were exposed to either control (0 MPs/L), low (10 MPs/L), or high (1000 MPs/L) MP treatments for 14 days. Using behavioral and cognitive assays, fish were assessed in inhibitory control, spatial learning, shyness, exploration, social motivation, feeding behavior, and aquatic surface respiration. We found that MP exposure elicited sex-specific cognitive impairment without affecting behavior or condition. Cognitive sex differences were suppressed under MP exposure. Under control conditions, males outperformed females in inhibitory control while females outperformed males in spatial learning. Under MP exposure, males exhibited a reduction in inhibitory control and females exhibited a loss in spatial learning resulting in no sexually dimorphic performance in either cognitive domain. Our results demonstrate that environmentally relevant MPs selectively impaired cognitive performance in a sex- and trait-specific manner without altering behavior or condition. Our findings highlight the importance of incorporating sex, dose, and cognitive endpoints when evaluating the consequences of MP pollution.