THE EFFECT OF DIETARY 17a-METHYLTESTOSTERONE ADMINISTRATION ON SECONDARY SEX COLORATION IN ADULT FEMALE ROSY BARBS AND DWARF GOURAMIS

Sexual phenotype is highly plastic in teleosts and controlled by a variety of species-dependent factors. In aquaculture, sex ratios are often manipulated to produce desirable phenotypic traits. In ornamental aquaculture, male fish are more valuable in many sexually dimorphic species due to more ornate coloration. These traits may be influenced after sexual differentiation by increasing the circulating androgen levels. This study investigated the effects of dietary 17α-methyltestosterone (MT) administration on adult female Rosy Barbs and Dwarf Gouramis . A panel of judges evaluated male secondary sex coloration weekly during and after prolonged MT feeding. Growth parameters, survival, and gonadosomatic index (GSI) were assessed at the end of the feeding regime. In both species, none of the MT diet concentrations affected survival and all resulted in coloration changes, highlighting both the efficacy and safety of MT administration. In Dwarf Gouramis, MT diets caused pronounced color changes and reduced their GSIs at all dietary concentrations. In Rosy Barbs, MT diets induced the expression of male coloration, but generally did not reach the color intensity of naturally occurring males and did not result in differences in GSIs. This study suggests that post differentiation androgenic treatment may be a viable option to induce secondary male sex coloration in ornamental species.