Induction of masculinization in Nile Tilapia (Oreochromis niloticus) through Dietary Administration of Anastrozole: Histological and Hormonal Insights.

The production of monosex male populations is a cornerstone for the efficient aquaculture of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758). The industry standard, methyltestosterone (MT), raises environmental concerns, necessitating alternative, targeted strategies. Aromatase inhibitors (AIs) offer a physiological approach by blocking estrogen synthesis, which is crucial for ovarian development. This study evaluated the efficacy of dietary administration of the potent non-steroidal AI, anastrozole, for inducing masculinization in Nile tilapia, assessing its effects on sex ratio, survival, gonadal histology, and key sex hormones. The post-yolk sac absorption fry were fed diets supplemented with anastrozole at 0 (control), 25, 50, 75, or 100 mg/kg for 30 days, followed by a 120-day grow-out phase. Phenotypic sex was determined, and gonadal histology was conducted for confirmation. Plasma levels of cortisol, testosterone, and estradiol (E2) were quantified using an ELISA kit. A dose-dependent increase in the proportion of males was observed, culminating in 100% phenotypic and histological males at the 100 mg/kg dose. Survival rates were significantly reduced at the 75 and 100 mg/kg doses. Hormonal analysis confirmed the mechanism of action: a dramatic, dose-dependent suppression of plasma E2 and a significant accumulation of testosterone in both sexes. Treatment also induced a significant stress response, as indicated by elevated cortisol levels. Dietary anastrozole is a highly effective alternative for producing 100% male Nile tilapia populations through targeted aromatase inhibition. The 75 mg/kg dose, yielding 91.43% males, is proposed as an optimal compromise for commercial application, balancing high masculinization efficiency with acceptable survival rates. The induced stress response warrants further investigation to optimize welfare protocols.