Aquaculture Crsp 21st Annual Technical Report

This study sought to determine whether administration of steroids via bioencapsulation into live food is an efficient method for sex inversion of carnivorous species of fish in aquaculture. This technique may offer an alternative for sex reversing such species because the larvae strongly prefer live food compared to artificial diets. To determine whether steroids could accumulate in Artemia, nauplii were immersed in solutions containing 2,500 mg L-1 of either estradiol (E2) or trenbolone acetate (TA). Steroids were dissolved in ethanol (1 mg ml-1) and then added to the water. Controls were immersed in water containing ethanol vehicle only. Each treatment consisted of three replicates. Water samples (50 ml) from glass jars containing Artemia nauplii were collected at 0, 2, 4, 6, 12, 16, 20, and 24 h. Nauplii were washed in nanopure water and dried, and samples were frozen (–20oC) and preserved until processed. All samples were extracted using ether, and the concentration of steroids were determined by radioimmunoassay (E2) or High Performance Liquid Chromatography HPLC (TA). Immediately after addition of steroids, nauplii contained > 1,500 ng g-1 of E2 and > 2,000 ng g-1 of TA. The nauplii treated with E2 contained 5,500 ng g-1 at 2 h, remained at that level until 6 h, and then reached a concentration of 7,000 ng g-1 at 12 h, which remained until 24 h. A similar pattern was observed when TA was used; however, at 24 h concentrations declined to 5,000 ng g-1. TA concentrations in Artemia nauplii enriched with highly unsaturated fatty acids (HUFA) ranged between 500 and 800 ng g-1. Despite these large differences in steroid concentrations between HUFA enriched and non-enriched Artemia, both methods resulted in significant sex inversion of fish fry. Both Nile tilapia and mojarra castarrica fry were masculinized (> 90% males) after being fed TA-en TWENTY-FIRST ANNUAL TECHNICAL REPORT 190 APPROPRIATE TECHNOLOGY RESEARCH 191 riched nauplii for 20 and 45 d, respectively. Tropical gars were also feminized (> 60% females) when fry were fed E2-enriched Artemia nauplii. It appears that bioencapsulation of steroids into Artemia nauplii is an efficient method for sex inversion of fish.