Oxidative stress: a sex-specific cost of parental care.

Parental care involves post-zygotic behaviors that promote offspring survival but can diminish parental survival and future reproductive potential. Although care is typically shared, males and females often differ in the nature and intensity of care provided. In the wild, we characterized pair formation and parental care (nesting and fry care) in Herichthys bartoni. Behavioral investment was quantified as the proportion of observation time allocated to each activity. Fin tissue samples were collected to evaluate oxidative stress across reproductive stages. We observed stage- and sex-specific behavioral differences. During pair formation, both sexes fed and engaged in synchronized swimming, with no significant sex differences. During nesting, females allocated a significantly greater proportion of observation time to nest cleaning and egg aeration, whereas no sex differences were found during fry care. Males were larger and exhibited higher total antioxidant levels, independent of body size. Antioxidant levels peaked during pair formation and fry care, with catalase activity being higher in females during fry care. No sex differences were detected in superoxide dismutase, hydrogen peroxide, or nitric oxide. These findings suggest that biparental care in H. bartoni involves distinct behavioral roles and physiological costs, with females bearing greater oxidative demands linked to their increased direct investment in offspring care.