Early gonadal development and effects of 17α-methyltestosterone-induced sex reversal on physiological parameters and gonadal gene expression in snakeskin gourami.

The plasticity period of sexual development facilitates sex manipulation in fish through exogenous hormone treatment. However, whether 17α-methyltestosterone (MT)-treated males exhibit growth performance and physiological traits similar to those of naturally genotyped males remains unclear. We evaluated MT treatment effects on growth performance, physiological and immune parameters, and gonadal gene expression in the snakeskin gourami Trichopodus pectoralis, and determined the optimal hormone intervention period. Early gonadal development was investigated via histological analysis and in-situ hybridisation of larvae using vasa and dnd probes at 3, 7, 14, 21, and 28 days post-hatching (dph). The presumptive gonadal region contained primordial germ cells (PGCs) at 3 and 7 dph, indicating migration. From 14 dph onwards, somatic cells were observed surrounding the PGCs within the genital ridge. PGC numbers appeared to increase at 21 dph, with more pronounced proliferation observed at 28 dph. Seven-day-old fry were fed a basal diet (control) or 100, 200, or 300 mg kg-1 MT-supplemented diets over 7-52 and 7-97 dph. MT-treated fish exhibited high masculinisation efficiency (81.16-94.44%). At sexual maturity, MT-treated fish growth was similar to that of males, but slower than that of females (P < 0.05). Haematological parameters or lysozyme activity did not differ. Male and MT-treated fish exhibited lower plasma glucose and triglyceride levels, whereas cholesterol, protein levels, and alternative complement activity exhibited MT dose-dependent effects. The gonadal gene expression profiles of the MT-treated fish closely resembled those of genetic males. Early MT feeding effectively produced sex-reversed males with a phenotype similar to that of genetic males. These findings support the development of neomale broodstocks for producing all-female populations.