Do Opposing Lipid Modulators Shape Gonadal Development in Juvenile Brown Trout?

Atorvastatin (ATV) and 17α-ethinylestradiol (EE2) are pharmaceuticals frequently detected in aquatic ecosystems, often at biologically active concentrations. ATV targets cholesterol synthesis by inhibiting HMG-CoA reductase, acting as a hypolipidemic agent, whereas EE2 is a potent estrogen receptor agonist that induces hyperlipidaemia. Given cholesterol's role in steroidogenesis and energy storage, both compounds may disrupt gonadal development and reproduction in fish. However, studies integrating and comparing the contrasting effects of these pharmaceuticals on fish reproduction remain limited, especially in juveniles, which are more susceptible to metabolic disturbances and altered gonadal development. This study aims to assess the effects of EE2 and ATV, using controlled doses to reflect environmentally and pharmacologically relevant exposures, on gonadal development in juvenile (1.5-year-old) brown trout (Salmo trutta), an emerging model organism for biomedical research. Thirty fish were randomly assigned to five experimental groups: solvent control, low EE2 (0.2 µg/g body weight), high EE2 (2 µg/g body weight), low ATV (0.03 µg/g body weight), and high ATV (0.3 µg/g body weight). Treatments were administered via intramuscular injection every 72 hours over a 28-day exposure period to ensure reproducible dosing and minimise variability in uptake. At the end of the exposure, gonads were collected, weighed, and processed for histology. Gonadosomatic index and gonad staging were evaluated, and immunohistochemistry for proliferating cell nuclear antigen (PCNA) and cleaved caspase-3 was performed. GSI did not differ significantly among groups. All males had juvenile testes, while ~60% of females had stage I ovaries, with no treatment-related differences in staging. Qualitative analysis of PCNA expression revealed no apparent treatment-related effects, whereas EE2 exposure suggested an increase in caspase-3 in both sexes. Although preliminary, these results suggest that EE2 may promote caspase-3-mediated apoptosis, potentially disrupting early gonadal remodelling and homeostasis. Ongoing work will include additional markers to better characterise the impacts of these lipid modulators.