Adult Paclobutrazol Exposure Impairs Zebrafish Reproduction: Evidence from Fertility Outcomes and Gonadal Histology

Paclobutrazol (PBZ), a triazole-based plant growth retardant, is widely employed in agriculture and horticulture to control plant height and promote root growth. However, its persistence and mobility in the environment raise concerns regarding its bioavailability and toxicity in aquatic ecosystems. In this study, we investigated the reproductive toxicity of PBZ in zebrafish (Danio rerio), a well-established model for aquatic toxicology and vertebrate reproductive research. Adult zebrafish were exposed to PBZ (0, 0.1, 1 ppm) for 2, 4, 6, or 8 weeks. After exposure, breeding was conducted using exposed or unexposed pairs to assess maternal, paternal, and combined effects on reproduction. Fertilization and hatching rates were quantified, and gonads were processed for histological evaluation. Chronic PBZ exposure significantly reduced fertilization and hatching success in both sexes, especially at higher concentrations and longer exposure durations. Histological examination revealed a reduction in testicular cyst area without significant changes in gonadosomatic index (GSI). In ovaries, structural integrity remained largely intact, although a mild increase in atretic follicles was observed. These findings demonstrate that PBZ impairs zebrafish reproductive success through subtle but consequential gonadal disruptions and suggest potential risks to aquatic biodiversity and population sustainability.