Sex differentiation and hormonal sex reversal in the bagrid catfish Pseudobagrus fulvidraco (Richardson)

Abstract

Sex differentiation of the bagrid catfish Pseudobagrus fulvidraco (Richardson) is described from hatching to the 100th day post-hatch (water temperature 25 °C). Primordial germ cells (PGCs) were observed on the 3rd day post-hatch (0.78 cm total length (TL), 0.006 g body weight (BW)), and began to protrude into the peritoneal cavity from the 8th day post-hatch (1.17 cm TL, 0.02 g BW). On the 12th day post-hatch (1.46 cm TL, 0.06 g BW), initial ovarian differentiation was identified by the PGCs with condensed chromatin, and their transformation into meiotic oocytes. Oocytes were in the secondary and tertiary yolk stages on the 100th day post-hatch (10.04 cm TL, 11.38 g BW). While ovaries gradually grew after sex were differentiated, testes continued to multiply from the 20th day post-hatch (2.30 cm TL, 0.24 g BW) when testicular differentiation was first identified. On the 100th day post-hatch (9.84 cm TL, 12.79 g BW), testes contained spermatocytes exhibiting meiotic activity, spermatozoa and cyst cells. Therefore, the sex differentiation type of the bagrid catfish is identified as gonochoristic. Effect of oral administration of either estradiol-17β (5–40 ppm) or tamoxifen (25–200 ppm) for 20 days (from 3rd to 20th day post-hatch) on mortality and growth of the bagrid catfish was studied. Estradiol-17β treatment at the concentration of 400 ppm successfully produced 100% females; however, estradiol-17β treatment induced mortality seemingly related to dose-dependent. Estradiol fashion did not affect growth of the bagrid catfish at doses of 0–20 ppm ( P>0.05), but significant growth depression occurred at 40 ppm ( P<0.05). Tamoxifen treatment at 200 ppm produced 90% males and mortality appeared to be dose-dependent. All groups of tamoxifen-treated fish exhibited significant growth acceleration comparing to the control group, but no significant difference was observed among the treated groups ( P>0.05). The combined results of oral administration with estradiol-17β and tamoxifen suggest that these hormones be effective for sex reversal in the bagrid catfish and the labile period of sex differentiation fall between the 8th and 30th day post-hatch.