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 17αmethyltestosterone (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 Significance Statement: This study examined the effects of multiple 17α-methyltestosterone larval administration regimes on the resulting sex ratios of two commercially important sexually dichromic ornamental fish species. The results of this study contradict the normal findings of 17α-methyltestosterone (MT) research and suggest sex reversal may not be easily achieved in these two species.

A regulatory cost assessment of ornamental aquaculture farms in Florida

“…The three commonly reported drugs and chemicals were MT, Dylox 420 SL, and Baytex. Methyltestosterone is used internationally in ornamental aquaculture to create phenotypic males, which demand a higher market price because of their bright coloration and enhanced ornamentation (Ramee, Lipscomb, & DiMaggio, 2020) Fish and Aquatic Conservation, 2021). The drawbacks of this method are that the participants of the study have to constantly collect data to show progress toward eventual full approval, there is a fee involved with participating, and the program must be renewed annually.…”

“…The three commonly reported drugs and chemicals were MT, Dylox 420 SL, and Baytex. Methyltestosterone is used internationally in ornamental aquaculture to create phenotypic males, which demand a higher market price because of their bright coloration and enhanced ornamentation (Ramee, Lipscomb, & DiMaggio, 2020). However, methyltestosterone is currently prohibited for use in the United States under the Anabolic Steroid Act of 2004 and is classified as a controlled substance (Anabolic Steriods Control Act, 2004).…”

Effects of synthetic androgen (17α-methyltestosterone) and estrogen (17β-estradiol) on growth and skin coloration in emperor red cichlid, Aulonocara nyassae (Actinopterygii: Cichliformes: Cichlidae)

“…Moreover, Phelps and Okoko (2011) observed the highest male rate (99.3%) in 30 mg • kg -1 MT supplemented fish group in O. niloticus and Kipouros et al (2011) obtained 100% males in groups supplemented with 2, 3, and 4 mg • kg -1 17α-MT. On the contrary, 17α-MT supplementation did not cause any significant difference in rosy barb and dwarf gourami (Ramee et al 2020), as well as in C. carpio (see Basavaraju et al 2008). The findings of the presently reported study suggest that hormone supplementation positively impacts the production of all male fish, thereby fetching a higher market value and increased profitability.…”

The effect of dietary 17α‐methyltestosterone administration on secondary sex coloration in adult female Rosy Barbs and Dwarf Gouramis

“…Masculinization research has generally focused on hormone administration to larvae during the critical labile period in order to induce permanent masculinization (Pandian, 2015;Wang et al, 2019). However, this technique is not always effective as demonstrated by previous studies (Ramee et al, 2020). In food fish aquaculture, the benefits of monosex culture include faster growth rates or limiting reproduction and require the desired sexual phenotype throughout the production cycle.…”

“…These are two sexually dichromic, gonochoristic species that were specifically identified by Florida's ornamental aquaculture producers as species that would benefit from masculinization techniques. Previous studies focusing on larval environmental manipulation and hormonal administration have not identified effective methods that consistently produce male‐skewed cohorts (Ramee, Lipscomb, & DiMaggio, 2020). Moreover, U.S. producers have lost most of the domestic market for both species as they are unable to compete with imported fish that have been treated with MT to express secondary male sexual characteristics (C. A. Watson, personal communication).…”