Diurnal rhythm of steroid biosynthesis in the testis of terminal phase male of protogynous wrasse, Pseudolabrus sieboldi, a daily spawner

The wrasse, Pseudolabrus sieboldi, is a diandric protogynous labrid fish. Spawning is performed by a terminal phase (TP) male and an initial phase (IP) female between 6:00 and 9:00 h daily during two-month-long spawning season. In the present study, to investigate the roles of steroid hormones in the diurnal spermatogenesis of the P. sieboldi TP male, all steroid hormones produced in the testis were identified and the synthetic pathways of these steroids were determined. Furthermore, the circulating levels of the major steroids produced were analyzed throughout a day at 3-hour intervals during spawning season. In the testis, 11-ketotestosterone (11-KT), estradiol-17β (E2), 17,20β-dihydoxy-4-pregnane-3-one (17,20β-P) and 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S) were synthesized as the major metabolites. In vitro steroid biosynthesis experiments showed similar results to the circulation profiles of the major steroids. This study is the first to clarify the complete steroidogenic pathways in the gonads of a diandric protogynous species throughout its life, when combined with the results of the steroidogenesis in the ovarian follicles. This is also the first report of a clear diurnal rhythm of the steroid production corresponding to the spermatogenic process in the testis of a male teleost.     

Isolation, cloning, sequencing of brain type aromatase and its expression in male and female Wrasse, Pseudolabrus sieboldi

Pseudolabrus sieboldi, wrasse being a diurnal spawner provides a good opportunity to study the endocrine mechanism of estrogen formation in brain and gonads. Moreover, an extremely large amount of E2 was produced in serum and testis of wrasse. It is assumed that the presence of E2 may play a major role in diurnal gametogenesis in male fish. In this study brain type aromatase have been isolated, cloned and sequenced from the brain of wrasse. Further, the expression pattern of brain type aromatase in gonads and adult tissue of male and female fish have been analyzed. In addition, the diurnal expression pattern of brain type aromatase in both male and female fish brain during spawning season have been analyzed. The P450arom (br) was isolated, cloned and sequenced from both male and female bamboleaf wrasse. The P450arom (br) gene (1877 sequenced nucleotide) contains an ORF of 1470 bp, a 5′-UTR of 18 bp and at least 407 bp in 3′-UTR. The amino acid sequence homology in the coding region of wrasse P450arom (br) is high compared to that of medaka, Oryzias latipes (80%), rainbow trout type 2, Oncorhynchu mykiss (78.2%), fugu, Takifugu ribripes (78%) rainbow trout type 1, (76%), goldfish, Carassius auratus (66.8%) and zebrafish, Danio rerio (66.2%). Expression study reveals that P450arom (br) mRNA were most abundant in brains of both male and female fish throughout the day during the spawning season. RT-PCR study revealed that P450arom (br) was expressed in skin, anal fin and tail fin of both male and female wrasse. P450arom (br) was not detected at any time of the spawning day in either ovary or testis of wrasse.     

Role of steriod hormones in sex change of protogynous wrasse

The endocrine mechanisms of sequential hermaphroditism were investigated in protogynous wrasse, Halichoeres trimaculatus. Administration of aromatase inhibitor and androgen both stimulated sex change, while estrogen suppressed the induced sex inversion. The results suggest that removal of estrogen is a key step to initiate sex change.     

Survival of ovarian somatic cells during sex change in the protogynous wrasse, Halichoeres trimaculatus

The three-spot wrasse (Halichoeres trimaculatus), which inhabits the coral reefs of Okinawa, changes sex from female to male. Sex change in this species is controlled by a social system. Oocytes disappear completely from the ovary, and male germ cells and somatic cells comprising testicular tissue arise a new during the sex change process. However, little is known of the fate and origin of the gonadal tissue-forming cells during sex change. In particular, the fate of ovarian somatic cells has not been determined, although the ovarian tissue regresses histologically. To approach this question, we analyzed apoptosis and cell proliferation in the sex-changing gonads. Unexpectedly, we found that few apoptotic somatic cells were present during sex change, suggesting that ovarian somatic cells might survive during the regression of the ovarian tissue. On the other hand, cell proliferation was detected in many granulosa cells surrounding the degenerating oocytes, a few epithelial cells covering ovigerous lamella and a few somatic cells associated with gonial germ cells at an early stage of sex change. Then, we found that proliferative ovarian somatic cells remained in the gonads late in the sex change process. Based on these results, we concluded that some functional somatic cells of the ovary are reused as testicular somatic cells during the gonadal sex change in the three-spot wrasse.     

Embryonic development in corkwing wrasse,Symphodus melops

Corkwing wrasse, Symphodus melops, is one of the main species used as cleaner fish to combat sea lice infestation in salmon aquaculture; however, there is little knowledge about its biology. Here, we describe the embryonic development of this species and examine the viability of the eggs under three temperature regimes. The experiments were conducted at three water temperature regimes, 12, 15, and 18°C, which resemble common sea water temperatures registered during the spawning season of corkwing wrasse at different latitudes along the Norwegian coast. Corkwing wrasse spawn small spherical eggs of 0.75–0.80 mm in diameter (mean 0.78, CV = 3.6%) with several oil droplets and go through eight developmental stages until hatching. The shortest hatching time was registered after 144 hr at 18°C and after 222 and 372 hr at 15 and 12°C, respectively. These observations provide important baseline biological information to advance the establishment of commercial rearing techniques and sustainable fishing management practices for this heavily exploited species.     

Environmental and fishing effects on the abundance,size and sex ratio of the blue‐throated wrasse,Notolabrus tetricus,on South Australian coastal reefs

Abstract The blue‐throated wrasse, Notolabrus tetricus (Richardson), is a site‐attached protogynous hermaphroditic species, with a small home range of 1000–2000 m², and the most abundant fish on inshore coastal reefs of South Australia. Long‐term studies over 18–24 years were conducted at an island reserve site and a fished mainland reference site. At the reserve site the retention rate of fish (reduced by mortality + emigration) was directly correlated with female mean size; the female:male sex ratio ranged from 10 to 20:1, consistent with an induction‐inhibition model of sex‐change. At the fished reference site, female mean size declined under intense fishing, and the sex ratio became strongly skewed towards females. Additional spatial surveys over >2000 km of coast showed that: (1) juvenile and adult abundance was variously determined by habitat features, such as substratum‐type, depth, bottom relief, wave exposure and algal canopy cover, and by geographical factors, such as distance off‐shore and within gulfs; and (2) that female mean size and the sex ratio were strongly influenced by recreational fishing, and to a small extent by bottom relief and other factors. The results suggest that female mean size and the sex ratio together can be used as an indicator of recreational fishing intensity at local scales. As populations of sequential hermaphroditic species are sensitive to size‐selective harvesting, management measures should aim to prevent sperm limitation, reproductive failure and skewed sex ratios in this species.     

Gonadal steroidogenesis and the possible role of steroid glucuronides as sex pheromones in two species of teleosts

In general, female zebrafish,Brachydanio rerio, ovulate only in the presence of males. The stimulant must be pheromonal as even male holding water is capable of inducing ovulation. After ovulation the mating phase begins. During this phase the male follows the female and oviposition as well as fertilization takes place. Both the ovulation and the mating are controlled by pheromones synthesized by the gonads. Ovulation can be induced by testicular homogenates. After the lipid material has been extracted from the testicular homogenates, the remaining aqueous phase can still induce ovulation. However, when the aqueous phase is treated with the enzyme-glucuronidase, it loses the ability to induce ovulation. This is an indication that glucuronides, probably steroid glucuronides, are the compounds responsible.During the mating phase, ovulated female zebrafish become attractive to males. It was found that, after ovulation, ovarian extracts contain the compounds responsible for attracting males. The attractant consists of a mixture of steroid glucuronides.After incubation of the gonads with³H-precursors seven steroid glucuronides have been identified in the testis and five in the ovary.Under fish culture conditions the African catfish,Clarias gariepinus, can produce postivitellogenic oocytes throughout the year. However, in capitivity neither males nor females spawn. In female catfish maturation and ovulation can be induced by treatment with gonadotropins. It might be possible that, analogous to the zebrafish, some reproductive processes in the catfish have to be induced by pheromones. It has been demonstrated that pheromonal compounds released by the seminal vesicles are involved in the attraction of female conspecifics. The steroid glucuronide synthesizing capability of the testes and the seminal vesicles of the male catfish are examined, as well as that of the ovary before and after ovulation of the female catfish. Both testes and seminal vesicles appear to be capable of steroid biosynthesis but only the latter synthesizes steroid glucuronides. Six of these conjugates have been isolated and identified. In the female catfish the ovaries are capable of synthesizing seven steroid glucuronides, but only after ovulation.     

雌雄同体鱼类性别分化及性转变研究进展

在脊椎动物中,鱼类具有多样的性别分化方式,大致可分为雌雄异体、雌雄同体以及单性生殖3类.一般情况下,鱼类性别决定后,性腺可分化为卵巢或精巢,并且在整个生命周期内保持不变.而在雌雄同体鱼类,其性别可以从雌性转变为雄性、雄性转变为雌性或者在雌雄两种性别间进行多次转变.雌雄同体鱼类具有多种性别转变形式,是研究脊椎动物性别决定...     

红鳍东方鲀gsdf基因的克隆及表达模式分析

该研究克隆了大黄鱼（Larimichthys crocea）gsdf （gonadal soma derived factor）和amh （anti-Müllerian hormone）基因的开放阅读框序列并对它们的表达进行分析。大黄鱼gsdf基因cDNA序列开放阅读框长为618 bp,可编码205个氨基酸,含有信号肽和TGF-β结构域。系统进化分析显示,大黄鱼Gsdf与其他鱼类Gsdf聚为一枝,而与TGF-β超家族其他成员分开。Amh基因cDNA序列开放阅读框为1 563 bp,可编码520个氨基酸,含有信号肽、AMH-N区域和TGF-β保守结构域。系统进化分析显示,大黄鱼Amh与舌齿鲈(Dicentrarchus labrax)Amh进化关系最近。荧光定量PCR表达分析显示,gsdf和amh基因主要在大黄鱼性腺表达,在精巢中的表达量显著高于卵巢（P < 0.05）,2个基因都在性腺分化前开始表达,在雄鱼精巢中表达量呈现先升高后下降的趋势,在卵巢的表达量很低。此外,相比于正常雌鱼,gsdf和amh基因在伪雄鱼（遗传性雌鱼）性腺中的表达量显著上调。这些结果表明,gsdf和amh基因在大黄鱼性腺分化过程中起到重要的作用。

     

Molecular cloning and expression of caspase-3 in the protandrous cinnamon clownfish, Amphiprion melanopus, during sex change

The caspase-3 appears to be a key protease in the apoptotic pathway. We identified caspase-3 complementary DNAs from the ovaries of the protandrous cinnamon clownfish (Amphiprion melanopus), and investigated its mRNA and proteins, and activity levels during the sex change (I, mature male; II, male at 90 days after removing of the female; and III, mature female). The nucleotide sequence of the caspase-3 cDNA was 969 base pairs in length with open reading frames encoding peptides of 282 amino acids. The caspase-3 mRNA and protein, and activity levels in stages of the mature gonad are higher than those of the development gonad stage. To understand the effect of gonadotropin-releasing hormone (GnRH) on gonad apoptosis, we examined expression of genes caspase-3 mRNA and activity level in immature cinnamon clownfish gonads after GnRH analogue (GnRHa). The findings support the hypothesis that caspase-3 expression is associated with both testicular and ovarian development, and suggests that it may play a role in the control of ovarian development in cinnamon clownfish. Also, we demonstrate that GnRH agonists stimulate caspase-3 production which can in turn stimulate apoptosis. The present study provides a framework for better understanding of the role of caspase-3 during sex change processes in fish.     

Susceptibility of corkwing wrasse Symphodus melops, goldsinny wrasse Ctenolabrus rupestis, and Atlantic salmon Salmo salar smolt, to experimental challenge with Vibrio tapetis and Vibrio splendidus isolated from corkwing wrasse

The virulence of two Vibrio strains, previously isolated from diseased corkwing wrasse Symphodus melops and identified as V. tapetis and V. splendidus, to corkwing and goldsinny wrasse Ctenolabrus rupestris and to Atlantic salmon Salmo salar, was studied under laboratory conditions. Both bacteria were shown to be opportunistically pathogenic to corkwing wrasse, causing significantly higher mortality in the challenged groups than in the controls. Bacterial cultivation of kidney samples and re-isolation of V. tapetis and V. splendidus from most mortalities confirmed the two strains as the probable cause of mortality in the challenged groups. The control group also suffered relatively high mortality, but no specific pathogens that were suspected to be the main cause of death were isolated, other than a mixture of Vibrio spp. and, in the case of one individual, atypical Aeromonas salmonicida. Following injection challenge with both bacterial strains, no mortality was recorded in Atlantic salmon. In bath challenge trials with goldsinny wrasse, only slight mortality was observed in the challenged groups and the unchallenged control group. Bacterial examination showed that atypical Aeromonas salmonicida was the probable cause of death in both bath challenged and control groups of goldsinny wrasse, and no indication of infection by any Vibrio sp. was found.     

Aeromonas salmonicida infectivity studies in goldsinny wrasse, Ctenolabrus rupestris (L.)

Goldsinny wrasse, Ctenolabrus rupestris (L.). were experimentally and naturally infected with Aeromonas salmonicida. Goldsinny wrasse were found to be susceptible to infection with A. salmonicida but significantly more resistant to infection than Atlantic salmon, Salmo salar L. The pathology of the acute infection is described. Following infection significantly higher levels of agglutinating antibody were detected in the sera of recovered wrasse than those observed in the Atlantic salmon controls. However, a large proportion of the recovered wrasse were culture positive for A. salmonicida and appeared to have entered a chronic stage of infection quite distinct from the carrier status that can develop in Atlantic salmon. This study indicates that, although goldsinny wrasse are susceptible to A. salmonicida, these fish are unlikely to become primarily infected, but contract furunculosis from infected Atlantic salmon. However, goldsinny wrasse may act as a reservoir for subsequent infections of cultivated Atlantic salmon because of the development of a chronic form of the disease. The potential for the vaccination of goldsinny wrasse against furunculosis is discussed.     

东太平洋赤道海域茎柔鱼组织能量积累及其与海表面环境因子的关系

为了从能量积累角度掌握茎柔鱼 (Dosidicus gigas) 的生活史策略,利用组织能量密度测定技术和广义线性混合效应模型 (Generalized linear mixed-effects models, GLMM) 对东太平洋茎柔鱼的肌肉、性腺等组织的相对能量积累及其与栖息海域环境因子之间的关系进行了分析。结果显示,东太平洋茎柔鱼以肌肉组织能量积累为主 (相对能量积累占70%以上),性腺组织能量积累相对较低。在生理性发育期至功能性成熟期,肌肉组织相对能量积累下降显著,性腺组织相对能量积累明显;在功能性成熟期,肌肉组织相对能量积累回升显著。肌肉组织和性腺组织的相对能量积累与栖息海域海表温度无显著相关性,但与栖息海域叶绿素 a 质量浓度存在显著的效应关系,并与采样经度分布密切相关。研究表明,东太平洋茎柔鱼在性腺发育开始后能量积累逐渐增加对生殖发育的投入分配,但在繁殖产卵期保持较好的肌肉组织状态,肌肉、性腺组织的相对能量积累更多取决于栖息海域的初级生产力。     

Precocious sex change and spermatogenesis in the underyearling Malabar grouper Epinephelus malabaricus by androgen treatment

The Malabar grouper Epinephelus malabaricus is an important candidate species for commercial aquaculture in tropical and subtropical areas. In nature, this species requires more than 10 years to change sex from female to male and have active spermatogenic tissues in the testis. Thus, it is essential to find a means of producing sperm for seed production. This is the first report of artificial sex change in underyearling E. malabaricus . Female E. malabaricus with immature ovaries at 144 days post-hatch (DPH) were fed a diet with 17α-methyltestosterone (MT) at 50 μg g⁻¹ diet for 6 months. Sex change occurred in most of the treated fish, which had testis with all stages of spermatogenic germ cells including spermatozoa. In contrast, most of the control fish had immature ovaries. These results, which reveal that germ cells in the underyearling grouper have the ability to produce spermatozoa in response to exogenous androgen, demonstrate that sex change can be artificially induced during ovarian development.     

养殖牙鲆性类固醇激素的周年变化

通过放射性免疫方法测定和比较了养殖牙鲆(Paralichthys olivaceus)成鱼血清中两种重要的性类固醇激素—睾酮(T)和雌二醇(E2)的周年变化规律。在雄性个体中,从4月份开始,随着水温的升高及繁殖期的开始,T和E2含量显著上升并在6月份达到最高峰;之后,T和E2含量逐渐下降并在第二年3月左右降低至最低水平。雌性牙鲆个体的E2含量于3月份开始慢慢增高,于6月份达到最高峰;随后,E2的含量逐渐降低并在1月份达到最小值;而雌性个体中的T的含量在2月和6月份出现两次高峰。结果表明,T和E2对牙鲆的性腺发育具有十分重要的作用,在雌雄个体中T和E2均呈现出周期性的变化。     

波纹唇鱼肌肉中营养成分分析

通过对波纹唇鱼肌肉氨基酸、脂肪酸等营养成分的测定和分析,评估和讨论其肉质的风味特征。结果表明,波纹唇鱼Cheilinus undulates的含肉率为71.5%,肌肉中粗蛋白、粗脂肪、粗灰分、水分的含量分别为18.98%、1.56%、1.23%、76.33%;测定的18种氨基酸总量为878.1mg/g(干重),4种鲜味氨基酸含量为355.3mg/g(干重),是其美味的主要因素。DHA和EPA的含量分别为2.00和9.51mg/g,DHA和EPA含量占脂肪酸总量的12.76%。