Abstract
The Siamese fighting fish ( Betta splendens ) is an ornamental fish commercially produced and exported worldwide. Male fish usually reach higher prices in the market, making masculinization protocols for producing male populations economically attractive. Steroid administration through dietary supplementation is one of the most commonly used methods for sex reversal in aquaculture. However, inert diets are not well accepted by B. splendens larvae. In this context, bioencapsulation techniques might represent an effective alternative for an oral hormone delivery during early development. This study developed a masculinization protocol for B. splendens using Artemia sp. bioencapsulated with 17α-methyltestosterone (17α-MT). Results showed that masculinization increased along with increasing 17α-MT enrichment, with the most consistent results observed at 30 and 40 mg L −1 , which yielded sex ratios above 0.85 compared with 0.50 in the control group. Fish weight, length, and survival rates were not affected by the tested concentrations of 17α-MT. These results demonstrate that the administration of androgen steroids bioencapsulated in Artemia nauplii could be considered an effective and safe strategy for the masculinization of B. splendens .