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.

We investigated the in vitro effects of nonylphenol (NP) and 3,3′,4,4′,5-pentachlorobiphenyl (PCB126) on steroidogenesis in redlip mullet, Chelon haematocheilus, oocytes. In experiment 1, we investigated the effects of NP and PCB126 on steroid production from exogenous steroid precursors. Vitellogenic oocytes (0.75 mm in diameter) were incubated with 10 and 100 ng/ml NP or PCB126 with [³H]17α-hydroxyprogesterone as a precursor. The major metabolites produced were androstenedione, testosterone (T), estrone, and estradiol-17β (E₂). Both NP and PCB126 increased T production and decreased E₂ production, except for 100 ng/ml PCB126. In experiment 2, oocytes (0.65–0.75 mm in diameter) were exposed to NP and PCB126 at different concentrations (0.01, 0.1, 1, 10, and 100 ng/mL). After the incubation, T and E₂ production was measured by radioimmunoassay. NP inhibited E₂ production at concentrations of 0.01 and 0.1 ng/ml in 0.75-mm-diameter oocytes. NP at 1 and 100 ng/mL stimulated T production, but had no observable effect on E₂ production. PCB126 treatment did not affect E₂ production at any of the concentrations tested. NP alone at 0.1 ng/mL resulted in a significant decrease in E₂ production in 0.65-mm-diameter oocytes. PCB126 did not show any significant effects on either T or E₂ production at all concentrations tested. These results suggest that NP acts like an antiestrogen at lower concentrations (0.01–0.1 ng/ml) in vitellogenic oocytes of redlip mullet.

We studied steroid metabolites produced from red-spotted grouper ovarian follicles during maturation. Oocytes with 350–500 μm diameter were in vitro incubated in the presence of [3H] 17α-hydroxyprogesterone as a precursor. Steroid metabolites were extracted from incubated media and oocytes. The extracts were separated and identified using thin layer chromatography, high performance liquid chromatography and gas chromatography-mass spectrometry. The identified metabolites were androstenedione (A4), testosterone (T) and estrone (E1). The metabolites of A4 was dominant in all size of oocytes and it was the highest in 480 μm diameter oocytes. The metabolites of two progestins, 17α,20β-dihydroxy-4-pregnen-3-one and 17α,20α-dihydroxy-4-pregnen-3-one were detected in the oocytes less than 480 μm diameter although they were not identified definitely. In the oocytes of 480 μm diameter, metabolite of progestin was the highest, and germinal vesicle (GV) was still in the middle of cytoplasm. In the oocytes of 500 μm diameter, GV was began to migrate and the major metabolites were A4 and E1. The metabolite of E1 was detected in all size of oocytes and it was higher than that of E2. These results suggest that oocytes of 480 μm diameter are the transitional stage involving steroidogenic shift to final oocyte maturation and potential function of E1 during maturation process.

Development of the cardiovascular system begins soon after gastrula concomitant with somite formation. In vertebrates, the cardiovascular system is the first functional organ system to arise and is critical in providing adequate oxygen and nutrient delivery to rapidly developing tissues (Chung & Ferrara, 2007; Patel-Hett & D'Amore, 2011). Cardiovascular system is very important in the developmental stages of the olive flounder life cycle. In most oviparous fish, including the olive flounder (Paralichthys olivaceus), embryo and larval survival depends upon timely vascular formation mediated by specific developmental gene expressions. Hypoxia triggers responses during developmental stage that play roles, cell to cell interaction and inhibit growth and development in fish purview from invertebrates to animals (Kajimura et al., 2006; Dunwoodie, 2009). To make sure survival in a variety of environments, fish embryos have evolved mechanisms to respond to hypoxia and repair oxygen homeostasis (Freeburg & Abrahamson, 2003). Because many embryonic tissues develop rapidly, they often outpace their vascular supply. Hypoxia-inducible genes are crucial regulatory proteins for the development of embryo to hypoxia, and they stimulate angiogenesis through activation of the vascular endothelial growth factor (VEGF) gene (Moeller et al., 2004; Liao &Johnson, 2007). Hypoxic stress response has been shown that rework the structure and mobility of endothelial cells in a way that contributes to a formation of vascular system. These mechanisms play an important role in blood vessel formation and communication with leukocytes as well as in regulation of intermediate filament in hypoxia response. The Intermediate filaments (IF) constitute one of the three major components of the cytoskeleton which also include actin microfilaments and tubulin microtubules (Goldman et al., 2012; Holthofer et al., 1984; Styers et al., 2005). Microtubules and actin filaments are dynamic structures known to play key roles in neuronal development and origin development, such as organization of neuronal cell, migration, axonal outgrowth, and intracellular transport, the functions of IF proteins in neurons have remained, until recently, more elusive (Hyder et al., 2007; Herrmann et al., 1989; Karabinos et al., 2001). The extracellular domains of desmocollin and desmoglein engage with their counterparts of adjacent cells to form the intercellular connection. In addition, in the myoplasm, intermediate filaments connect to dense bodies to which actin filaments also attach (Fuchs & Cleveland, 1998; Prahlad et al., 1998). These structures act in concert to control cell morphology and biomechanics. Vimentin is a main intermediate filament protein in airway and vascular tubule, whereas latest is expressed in smooth muscle (Qin et al., 2009) and micro arteries (Guo et al., 2005; Nekrasova et al., 2007).

Effects of changes in photoperiod on the reproductive events in fish are suggested to be mediated mainly via the action of melatonin (MEL). Changing levels of plasma MEL throughout the day and year are suggested to influence the hypothalamus–pituitary–gonadal axis in fish. Therefore, in this study, we aimed to investigate the effects of MEL on oocyte maturation and germinal vesicle breakdown (GVBD) in the marine fish, Chaenogobius annularis, in vitro. Oocytes at three different stages (pre-, mid-, and late-vitellogenesis) were incubated with (a) only MEL (5, 10, 50, 100, 500, and 1,000 pg/mL) and (b) 50 pg/mL of 17α,20β-dihydroxy-4-pregnen-3-one (17α20βP), maturation-inducing hormone (MIH) of this species, and MEL (4-h incubation before addition of MIH). Any single MEL treatment did not significantly induce GVBD. However, treatment with 50 pg/mL MEL or MIH significantly induced GVBD. These results suggest that preincubation with MEL accelerates the effect of MIH on longchin goby oocyte maturation.