Effects of 17α-methyltestosterone feeding and immersion on masculinization of rosy barbs Pethia conchonius and dwarf gouramis Trichogaster lalius

Abstract

Hormone treatments have commonly been used to skew sex ratios toward desired phenotypes. In sexually dichromic ornamental species, males are often more ornately colored and therefore more valuable. The synthetic androgen 17α-methyltestosterone (MT) is one of the most common hormones used in this practice. The rosy barb, Pethia conchonius, and dwarf gourami, Trichogaster lalius, are two sexually dichromic species that would benefit from masculinization. The larvae of T. lalius and Pethia conchonius were exposed to MT over the first 30–60 days posthatch either through a series of 4-hr immersions (0, 100, 200, 400, or 800 μg MT/L) or via top-coated feed (0, 15, 30, 60, 120, 150, or 250 mg MT/kg feed). Survival was determined at the end of each treatment regime, and sex ratios were determined via gross dissections. In rosy barbs, none of the 30-day treatments resulted in significant masculinization. MT feeding for 60 days resulted in more than 85% males in P. conchonius, but this was not significantly different from the control (70%). In T. lalius, paradoxical feminization was observed in immersion concentrations and 50 days of MT feed treatments.