Oral exposure to herbicide 2,4-D induces reproductive toxicity in the silver catfish Rhamdia quelen

We investigated the reproductive effects of 2,4-D in Rhamdia quelen fish orally exposed to permissive and environmental doses: 0.02, 0.2 and 2 mg kg−1. An outdoor experiment with controlled conditions in fish combined with a designed sampling procedure aimed to evaluate somatic and histological reproductive effects. These results were corroborated by the molecular detection of vitellogenin (VTG) in both sexes. In males, the damage was significantly greater in the 2,4-D-treated groups (22 days: G = 36.17; p < 0.001; 44 days: G = 29.87; p < 0.001) at all doses, ranging from asynchronous development and an increase in spermatogonia to hermaphroditism. Males were more sensitive than females, as supported by somatic (K) and histopathological indices (Bernet’s index), and VTG detection of expression. There was an increase in the ovary’s maturation (differences in stages: G = 37.94; p < 0.001) and a decrease in the gonadossomatic index in females (0.2 and 2 mg kg⁻¹). Additionally, the histopathological index was higher at 0.02 mg kg−1 (22 days: G = 9.34; p = 0.025; 44 days: G = 24.01; p < 0.001), and VTG expression increased for all doses. 2,4-D caused significant changes in gonadal development in R. quelen, demonstrating estrogenic effects and potential risk to natural population dynamics.