• Journal of Aquaculture
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• v.20 no.1
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• pp.47-50
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• 2007

The primordial germ cells of the oblong rockfish, Sebastes oblongus were buried under fibrous mesenchymal tissues between gut and mesonephric duct of pre-larva with 4.0 mm total length (TL) at 1 day after the parturition. In the juvenile of 22.0 mm TL at 71 days after the parturition, the gonad composed of a large number of gonial cell and formed of cavity along the lateral side of the gonad, differentiated to the ovary. At this time, the gonad formed seminiferous tubules by somatic cells, was differentiated to the testis. The smallest oblong rockfish that possessed primary oocytes was about 42.1 mm TL at 141 days. Spermatogonia remained quiescent until most fish were over 42.1 mm TL at 141 days. The oblong rockfish the differentiated directly into male or female without an intermediate female phase at the early indifferentiated stage. Therefore, the oblong rockfish belongs to the differentiated type of gonochoristic teleosts.

• Korean Journal of Ichthyology
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• v.19 no.2
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• pp.107-111
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• 2007

Sex differentiation of the brown croaker Miichthys miiuy (Basilewsky) is described from hatching to the 120th day post-hatching (dph) (water temperature $24^{\circ}C$). Primordial germ cells (PGCs) were observed on the 20th dph (10.4 mm total length (TL), 0.14 g body weight (BW), and began to protrude into the peritoneal cavity from the 40th dph (19.4 mm TL, 0.39 g BW). On the 65th dph (31.3 mm TL, 0.93 g BW, $1,560D^{\circ}$ (degree-days)), initial ovarian differentiation was identified by the PGCs with condensed chromatin, and their transformation into meiotic oocytes. By the 120th dph (4.60 mm TL, 1.38 g BW, $2,880D^{\circ}$), the oocytes were in the perinucleolus stage and had increased from 20 to $40{\mu}m$ in diameter. While ovaries gradually grew after sex was differentiated, testes continued to multiply from the 65th dph. On the 80th dph (37.9 mm TL, 1.39 g BW, $1,920D^{\circ}$), the beginning of testis lobule formation was indicated by the occurrence of spermatogonial cysts enveloped by somatic cells in some of the testes. On the 120th dph, the testis lobules of some of the fish contained all germ cell stages through to the spermatocytes. Therefore, the sex differentiation type of the brown croaker is identified as gonochoristic.