Red spotted grouper, Epinephelus akaara is a popular aquaculture species in many Asian countries. This species is a protogynous hermaphrodite that first differentiates into female and changes to male later. Due to this reproductive characteristic, stable supply of male and female gametes is a key to the success of seed production in this species. Thus, understanding early gonadal differentiation is required to develop effective sex control techniques. Red spotted grouper were reared in indoor tanks and sampled every 5 days from 40 days post-hatch (DPH) to 130 DPH. Changes of gonadal tissues were examined and analyzed by means of histology. A pair of gonadal primordium has already existed underneath the kidney in the posterior part of the body cavity at 38 DPH when this study began. Gonadal primordia of 38, 40 DPH consisted of germ cells surrounded by a few somatic cells. The blood vessel was observed in the gonadal primordium at 45 DPH. The number of somatic cells and size of gonadal primordium increased age-dependently up to 60 DPH. Formation of ovarian cavity was obvious by two protuberant aggregations of somatic cells at 65 DPH. Completed ovarian cavity and oogonia were first observed in the gonad of one fish sample at 105 DPH. Based on these histological observations, it can be suggested that induction of primary male differentiation could be more successfully applied at around 60 DPH in this species.

Red spotted grouper (Epinephelus akaara) is one of the most popular and important grouper species for aquaculture in South-East and East Asia thanks to its fast growth and high market value. This species is known as a protogynous hermaphrodite which first differentiates into females and changes to males later. Natural sex change in this species occurs at 2 or 3 years of age. Many studies have been conducted, so far, to develop standardized methods for artificial sex reversal by treatment with sex steroid hormones (Bhandari et al., 2005; Lee et al., 2014). However, sex-changed male groupers showed testes with ovarian cavity, and their sperm production was very low. Induction of primary sex differentiation directly into males would be an alternative approach. Identification of the exact primary sex differentiation period is the prerequisite for this approach. Red spotted grouper were reared in indoor tanks and acclimatized at 25±2℃ under natural photoperiod. Fish were sampled at 60 days after hatching. The samples were processed for histological analysis using standard techniques in an automatic tissue processor, sectioned at 8 μm in thickness and stained with haematoxylin and eosin. The result of this study shows the morphological characteristics of gonadal primordium, and suggests that the timing of gonadal differentiation in red spotted grouper is at least 10 days earlier than the previous study of Lee et al. (2014) which observed gonadal primordium at 70 days after hatching.

This study describes the developmental process of gonads in chameleon goby, Tridentiger trigonocephalus from the stage of hatching to 100 days after hatching (DAH). Based on histological observation, the primordial germ cells were observed in mesentery between mesonephric duct and gut at 15 DAH (total length, TL: 6.8±0.2 mm). At 20 DAH (TL: 7.9±0.1 mm), the primordial gonad began to protrude into peritoneal cavity and developed between mesonephric duct and gut. Initial ovarian differentiation was identified by the presence of ovarian cavity and oogonia in the gonads at 55 DAH (TL: 21.1±1.3 mm). Testicular differentiation started at 65 DAH (TL: 23.7±0.9 mm) with appearance of spermatogonial cells in the gonads. These findings indicate that sex differentiation in T. trigonocephalus occurs earlier in females than males, suggesting that this species can be classified as an undifferentiated gonochorist.

For the gonadal sex management of younger longtooth grouper (Epinephelus bruneus), this work investigated the timing and histological process of ovary differentiation and oocyte development of longtooth grouper larvae and juvenile. Specimens (from 1 to 365 DAH) were collected for gonadal histological study from June 2008 to August 2009. Rearing water temperature was ranged from 20 to . The primordial germ cells could be observed from 10 to 15 DAH, while undifferentiated gonad occurs from 20 to 50 DAH in longtooth grouper. The initial ovarian phase was 60 to 110 DAH with the formation of ovarian cavity and the increased in size of gonad. The ovarian phase started at 140 DAH with appearance of oogonia. The gonad at 365 DAH appeared to have full of oogonia and primary growth stage oocyte. Formation of ovarian cavity indicates that the ovarian differentiation beginning at 60 DAH in longtooth grouper. The gonads in longtooth grouper differentiated directly into ovaries in all fish examined.

The transcription factors, DMRT1 and FOXL2, play a role in fish sex differentiation of the bipotential precursor into the male and female pathway, respectively. In order to provide the molecular background for understanding hormonal regulation in sexual determination and differentiation in the red-spotted grouper, Epinephelus akaara, one of commercially important epinephelines, and is often used to study protogynous sex change. First, we amplified the partial sequence of two genes (DMRT1 and FOXL2) from the gonad of red-spotted grouper. Also, we surveyed the tissue-specific and sex-specific expression pattern of each genes by RT-PCR. The effects of 17α-methyltestosterone (MT) in the sexually immature gonad of red-spotted grouper were investigated by Real-time quantitative RT-PCR. Fish were treated with MT-dipping method from around 70 days after hatching (DAH) for two month. DMRT1 and FOXL2 cDNA flagments consist of 489 and 836 base pairs (bp) and encodes a protein of 162 and 278 amino acids, respectively. RT-PCR revealed that DMRT1 mRNA was expressed higher level in the testis. Foxl2 was expressed extensively in the neural and peripheral tissues with its highest level in the ovary, indicating a potential role for Foxl2 in the brain-pituitary-gonad axis. Real-time quantitative RT-PCR analyses showed that DMRT1 mRNA expression was upregulated in the MT-treated fish. These results suggest that the sex inversion of red-spotted grouper by MT might be due to the suppression of FOXL2 gene expression, and resulting in the induction of the 11-KT secretion.

눈동자개, Pseudobagrus koreanus의 성분화 과정을 밝히기 위해 부화 직후부터 250일령까지 생식소의 분화 및 발달을 조사하였다. 원시생식세포는 부화 후 1일(전장: 6.63～6.95 ㎜)에 나타났으며, 부화 후 5일(7.50～9.36 ㎜)에 생식융기를 형성하는 원시생식소 구조를 나타내었다. 부화 후 25일(11.58～13.21 ㎜)에서는 생식소 후단부 한쪽 끝에서 신장된 체세포 돌기가 생식소와 융합되어 작은 난소강이 형성되었다. 부화 후 30일(12.19～13.72 ㎜)에는 생식소 하단부에 정소관 원기가 출현하여 정소의 분화가 시작되었다. 부화 후 50일째 자어(16.28～17.06 ㎜)의 난소내에서는 주변인기 난모세포로 채워지기 시작하였으며, 정소내에서는 정원세포(spermatogonia, SG)의 활발한 증식을 관찰할 수 있었다. 부화 후 250일째 자어(35.49～51.12 ㎜)에서는 난소의 크기가 더욱 커지고 난모세포들로 가득 채워져 있었고, 정원세포의 수가 증가하기 시작하였다. 이상의 결과 눈동자개의 성분화 양상은 자웅이체형 중 분화형이었다.

점농어, Lateolabrax maculatus의 성분화 과정을 밝히기 위해 부화 직후부터 365일령까지 생식소의 분화 및 발달을 조사하였다. 원시생식세포와 생식융기는 부화 후 30일령(전장: 11.7~13.2 mm)에 나타났으며,40일령 자어(12.5~14.0 mm)에서 서로 융합되어 미분화 생식소를 형성하였다. 60일령 치어(23.6~27.0 mm)에서는 생식소 양쪽 끝의 체세포조직이 분열ㆍ신장되어 난소의 분화가 개시되었고, 80일령 치어(33.1~

부화 후부터 평균전장 0.64 cm를 나타내는 부화 후 150일까지의 버들치, Rhynchocypris oxycephalus를 대상으로 초기생식소 발달과 성분화를 조사하였다. 시언생식세포는 평균전장 0.64cm 자어에서 뚜렷이 나타나\ulcorner. 평균전장 1.91 cm자어에서 시원생식세포는 복강으로돌출되었으며, 평균전장 2.29 cm 자어에서 시원생식세포는 감수분열 난모세포로 전환되었고, 난소로의 분화가 최초 확인되엇따. 평균전장 5.96 cm 자