Stages Of Gonadal Development Research Articles

Reproductive cycle and early development of Meretrix lamarkii (Veneroida: Veneridae) under artificial conditions

PDF HTML阅读 XML下载 导出引用 引用提醒 人工蓄养斧文蛤的生殖周期及早期发育 DOI: 作者: 作者单位: 1. 浙江省海洋水产养殖研究所, 浙江省近岸水域生物资源开发与保护重点实验室, 浙江 温州 325005;2. 中国水产科学研究院 海洋贝类工程技术研究中心, 浙江 温州 325005 作者简介: 邵艳卿(1979-),女,高级工程师,从事海洋贝类种质资源与遗传育种.E-mail:amshao@126.com 通讯作者: 中图分类号: S968 基金项目: 国家海洋公益性行业科研专项子任务（201205021-5）；国家水产种质资源平台项目（2015DKA30470）；温州市科技项目（S20110006）. Reproductive cycle and early development of Meretrix lamarkii (Veneroida: Veneridae) under artificial conditions Author: Affiliation: 1. Zhejiang Mariculture Research Institute, Zhejiang Key Lab of Exploitation and Preservation of Coastal Bio-Resource, Wenzhou 325005, China;2. Engineering Research Center for Marine Bivalves, Chinese Academy of Fishery Sciences, Wenzhou 325005, China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了探讨斧文蛤（ Deshayes）的繁殖规律和胚胎发育过程，自2012年1月至2013年1月，每月采集样品，采用组织学方法对浙南海区移养的斧文蛤性腺发育、生殖周期和性成熟率周年变化进行了研究，并结合室内人工育苗试验对其胚胎发育过程进行了显微观察。结果表明，该地区斧文蛤的性腺发育以1年为1个周期，可分为增殖期、生长期、成熟期、排放期和休止期5个时期，雌雄性比约为1：1，性腺发育时间基本同步，均始于2月，随着水温的升高而发育，大部分个体在6月至7月发育成熟，7月下旬至8月底是繁殖盛期，可用阴干加流水刺激方法诱导其排放精卵，受精卵在水温29℃、盐度28、pH 7.8~8.5条件下，经16~20 h孵化成D形幼虫，壳长为100~110 μm，浮游幼虫经5~6 d培育进入匍匐幼虫期，壳长约200 μm，最后发育变态为稚贝。本研究为斧文蛤的人工繁育、养殖开发以及种质资源保护提供了基础资料。 Abstract:The benthic marine bivalve, , is a commercially caught species and is exploited in many southern coastal cities of China, where it is sold by wet weight. However, efficient and effective management strategies are needed for a sustainable supply of this wild resource, and an understanding of reproductive biology and the fishery is required. The aim of this study was:(1) characterize gonadal morphology and histology; (2) describe the main gametogenic events and link them to maturation stage, and (3) characterize spawning, eggs, and newly hatched veliger larvae. Samples were collected monthly from January 2012 to January 2013 from Cangnan Bay, south of Zhejiang Province, China. Routine histological techniques were used to characterize the gonadal development stages. The results show that the clam is characterized by typical gonadal development of bivalves, and the reproductive cycle was divided into proliferation, growing, maturation, breeding, and suspensive stages. Gonadal maturation of clams from the South Zhejiang coast was completed over 1 year. The spawning season occurred from early June to mid-September, and peak spawning occurred from early July to mid-August, when water temperature was 24.8-29.4℃. This clam is dioecious, and gametes of both sexes are released at about the same time. The female to male ratio was 1:1. Spawning was induced by shade-drying or running seawater. Embryos developed in salinity of 28 and temperature of 29℃. The D-shaped larvae hatched after 16-20 hours at 29℃. The larvae developed into post-larvae and completed metamorphosis into spat after 5-6 days, with a mean shell length of 200 μm. 参考文献 相似文献 引证文献

Beberapa Aspek Reproduksi Siput Lambis lambis di Pesisir Perairan Yenusi, Biak

<strong>Some Aspects of Reproduction in Conch Lambis lambis of Yenusi Coastal Waters, Biak.</strong> Lambis lambis is a very popular conch species that has been harvested in all sizes encountered. This condition is very alarming because in the long term, its existence in nature will be reduced because there is no chance to reproduce naturally. This study aims to determine the sex ratio and gonad maturity levels of L. lambis in Yenusi waters, so the appropriate time of harvest can be arranged. Samples were collected every month from January to December 2013. Testing and histological analysis were performed in the laboratory. Samples collected were 99 individus with the number of males 45 individus and females 54 individus. The sex ratio of males and females was 1.0:1.2. Gonad maturity level found included all four stages of gonadal development, from TKG I to TKG IV. Gonadal development showed the process of formation and maturation, and the spawning occured throughout the year, with peak spawning in January until March 2013. The size of the shell length obtained ranged from 4.55 to 13.72 cm indicating over-exploitation. Due to the custom local where residents harvested the conches in all sizes found, sustainable management strategies are urgently needed, including moratorium period when L. lambis is at the peak of spawning, and harvest should only be performed on adult individuals with a minimum shell size of 7 cm, while observing the thickness of the shell and marginal digitations have been formed. <br /><br />

Reproductive cycle and releasing time for increase of resource of adult sea cucumber Apostichopus japonicus released to seed breeding grounds

ABSTRACTThe reproductive cycle and releasing time for effective increase of resource of adult sea cucumber (Apostichopus japonicus) have been studied in the west coast of Korea. Adult sea cucumbers collected in Seocheon-gun April 2013 for first release and in the uncontaminated Taean-gun area in the west coast of Korea. Divers monthly collected the specimens in the released area from December 2013 to November 2014 in order to investigate the reproductive cycle of A. japonicas in Taean-gun. Random specimens were dissected to examine the gonadal developmental stages and discharge rates of the guts and gonads. The reproductive cycle of A. japonicus in both sexes are classified into the following six successive stages in the Taean-gun: (1) Stage I (recovery stage from December to February), (2) Stage II (early growing stage from February to March), (3) Stage III (late growing stage from March to April), (4) Stage IV (mature stage from April to July), (5) Stage V (partly spawned stage in July), and (6) Stage VI (spent stage from August to November). The estivation period of this species is from July to October in the Taean-gun region while surface water temperature is approximately 20–25.4°C. Thus, the optimum period to easily harvest them is from October to November in the uncontaminated Taean-gun area. It is also the best releasing time because the recovery stage starts from December to February in the Taean-gun region.

A Novel igf3 Gene in Common Carp (Cyprinus carpio): Evidence for Its Role in Regulating Gonadal Development.

Since the insulin-like growth factor 3 (igf3) gene was recently discovered in fish ovary, its function in the gonads has received much attention. In this study, we isolated two igf3 subtypes from common carp (Cyprinus carpio), which comprised full-length cDNA of 707 and 1153 nucleotides encoding 205 and 198 amino acids (aa), respectively. The Igf3 aa sequence had the highest gene homology of 72% with the corresponding sequence in zebrafish (Danio rerio). Phylogenetic tree construction revealed that the C. carpio igf3 gene was first clustered with D. rerio and then with other teleost species. Igf3 mRNA was widely expressed, with expression being highest in the gonads and blood. In the gonad development stage, igf3a mRNA expression was highest in the maturity and recession stage of the ovary, and decline phase of the testis, while igf3b was highest in the recession and fully mature periods of the ovaries and testes, respectively. Western blotting of testis protein samples showed two bands of approximately 21 kDa and 34 kDa corresponding to the calculated molecular mass of the two Igf3 subtypes; no signal was detected in the ovary. The Igf3 protein was localized in the ovary granulosa cells and testis spermatogonium and spermatids. 17β-Ethinylestradiol treatment increased both ovary and testis igf3 mRNA expression. These findings suggest that Igf3 may play an important role in C. carpio gonadal development.

Aspects of reproduction of the brown mussel Perna perna at the Iture rocky beach near Cape Coast, Ghana

Aspects of the reproductive biology of the brown mussel Perna perna at the Iture rocky beach near Cape Coast, Ghana, were studied from September 2014 to August 2015. The current study was aimed at providing information useful for managing the mussel fishery in this locality and also that would form the basis for designing appropriate culture methods for the species. Microscopic examination of fresh smears of gonadal material, as well as histological preparations of the gonad, were used to study the sexuality and breeding pattern of the species. Monthly gonadal and condition indices were also determined. Perna perna exhibited gonochoristic sexuality with a sex ratio of approximately 1:1 throughout the study period. Sexes were identifiable at shell lengths of 15.0–19.9 mm. Five stages of gonadal development were identified in both sexes. Gametogenic activity was continuous throughout the year, with two major spawning activities, from April to June and from August to December. These periods coincided with the major and minor rainy seasons, respectively, as well as the major upwelling period in August. Condition indices suggest that the mussels were in better condition for harvesting in March and August prior to the major spawning events.

Molecular cloning, characterization and expression profile of kisspeptin1 and kisspeptin1 receptor at brain-pituitary-gonad (BPG) axis of golden mahseer, Tor putitora (Hamilton, 1822) during gonadal development.

Complete cDNA sequences of kiss1 (gmkiss1) and its receptor kiss1r (gmkiss1r) were cloned and characterized from brain tissue of adult golden mahseer (Tor putitora). Thereafter, quantification of gmkiss1 and gmkiss1r mRNA expression in brain-pituitary-gonad (BPG) axis of male and female golden mahseer was carried out using quantitative real-time (qRT)-PCR assay during an annual reproductive cycle, at different gonadal development stages. The gmkiss1 cDNA was 508bp, with 330bp open reading frame (ORF), encoding a precursor protein of 109 amino acids, whereas gmkiss1r cDNA was 1383bp with an ORF of 1004bp, which encodes a 334 amino acid protein residue. The qRT-PCR study shows that gmkiss1 and gmkiss1r are expressed in brain, pituitary and gonads of both the sexes of golden mahseer. An apparent sexual dimorphism in transcript level of gmkiss1 and gmkiss1r in brain and gonads was evident during the reproductive cycle. Overall, in brain, testis and ovary, the gmkiss1 and gmkiss1r mRNA expression level was comparatively higher during the initial stages of gonadal development, than that of spermiation or ovulation stage. In pituitary of both the sexes, throughout the gonadal development, consistently low transcript level of gmkiss1 and gmkiss1r was observed. The gmkiss1 mRNA expression level in brain and ovary of female golden mahseer was several folds higher than the brain and testis of male fish. In conclusion, we confirm the presence of kiss1 and its receptor in golden mahseer, and results of our study strongly suggested the involvement of kisspeptin1 system in gonadal development and annual reproductive cycle of this species.

Differential expression of foxl2 and cyp19a1a mRNA during gonad developmental stages in great sturgeon Huso huso.

This study aimed to determine the sex specificity and expression pattern of foxl2 and cyp19a1a genes in great sturgeon Huso huso gonads during gonadal sex differentiation and development. The results revealed that foxl2 and cyp19a1a mainly expressed in female gonads and during gonad development the foxl2 and cyp19a1a mRNA expression is required for ovarian development.

Reproducción de los róbalos Centropomus undecimalis y C. ensiferus (Perciformes: Centropomidae) en una laguna costera tropical

Snooks C. undecimalis and C. ensiferus are important fishery resources in their distribution area. In Venezuela they are caught by artisanal fisheries along the entire coast. However, studies on their biology that would help establish fishing regulations are scarce. To study reproduction aspects of these species, we analyzed 1 325 individuals of C. undecimalis and 2 025 of C. ensiferus caught by artisanal fishing in the Laguna de Tacarigua in Northern Venezuela, from July 2009 to September 2010. Total length, total weight, sex and stage of gonadal development were recorded. The sex ratio varied throughout the year: there was a significant difference in favor of C. undecimalis males (1.5:1), and C. ensiferus females (1:3.3). Differences were also evident in the sexual proportion at each size group. For both species, males dominated in the lower size ranges while females dominated in the larger size ranges. These results suggested sequential hermaphroditism (protrandry) in both species. Size at sexual maturity (Lm50) for C. undecimalis was ♀= 73.6 and ♂= 59.3 cm, and ♀= 26 and ♂= 21.5 cm for C. ensiferus. C. ensiferus reproduced throughout the year with two periods of higher intensity (August to September and February to April). Although we found very few mature individuals for C. undecimalis, February showed an important reproduction peak. Growth differences were found between males and females of C. undecimalis: positive allometry for females (P= 0.0022*L3.353) and negative allometry for males (P= 0.0108*L2.945). Both males and females of C. ensiferus showed a positive allometric relationship (P= 0.0049*L3.235). Lack of fishing regulations and controls, evidenced in this study by significant volumes of immature individuals in the catches, and the particular reproductive biology of these species, strongly indicates the need to establish regulations to ensure their responsible use. We recommend establishing a closed season during the first quarter of the year and minimum catch sizes for both species.

Benih Keturunan Induk Ikan Nila yang Divaksinasi pada Tingkat Kematangan Gonad-2 Lebih Tahan Terhadap Infeksi Streptococcus agalactiae (RESISTANCE OF TILAPIA (OREOCHRIMIS NILOTICUS) FRY VACCINATED AT DIFFERENT GONADAL DEVELOPMENTAL STAGES TOWARD STREPTOCOCCUS AGALACTIAE INFECTION)

The aim of this study was to evaluate the effectiveness of vaccination based on gonad maturationstages on tilapia brood stocks in which the released antibodies was able to be transferred to the seed.Vaccine composed with whole cells and extracellular product (ECP) was injected at stage 2 and stage 3 ofthe gonad development stages at concentration of 109 CFU mL1 as much as 4 mL to 1 kg of brood fish.Control fish was unvaccinated treatment. Challenge study at seed was conducted by immersing S. agalactiaefor 30 minutes at 7, 14, 21, and 28 days post hatching (DPH) in 107 CFU/mL. Antibody levels on broodstocks, eggs, and body fluids of seed, and relative percentage survival (RPS) of seed post challenge studywere evaluated. The results showed that stage 2 of gonad developmental stages was found on 7 days postinitial spawning and stage 3 found on 14 days post initial spawning of brood fish. Vaccinated done in stage 2 of gonad developmental stages gave immunoglobulin serum in brood (0,166±0,001), egg (0,165±0,002),and seed aged 7, 14, 21, and 28 days post hatching (0,164±0,002, 0,162±0,005, 0,155±0,006, and 0,14±0,008respectively) were significantly higher (P<0,05) compared to other treatment. Challenged test that doneby immersing with S. agalactiae suspension on larval aged 7, 14, 21, and 28 days had highest RPS(95,24%, 83,33%, 72,22%, and 56,02% respectively) formed on seed from brood stock vaccination in gonaddevelopment stage 2. Vaccination in tilapia brood stocks at stage 2 of gonad developmental stages gavehighest protection by maternal immunity to the seed against S. agalactiae.

A Window of MHM Demethylation Correlates with Key Events in Gonadal Differentiation in the Chicken

The MHM (male hypermethylated) region on the chicken Z chromosome is of interest in terms of sex determination both because hypermethylation of the promoter in males results in female-specific expression, and in females the non-coding transcripts accumulate in the region of a locus that encodes a key candidate gene for testis differentiation in birds - DMRT1. However, it has yet to be established whether MHM plays a role in either sex determination or gonadal development in chicken. Here, we sought to establish the MHM methylation pattern during chicken gonadal development and determine how this pattern correlates with the expression profiles of genes involved in sex determination and gonadal differentiation. As expected, we found that MHM methylation levels were higher in male than in female gonads at most stages of development. We also showed that there was no significant difference in the methylation patterns between the right and left gonad and that the pattern of methylation in female gonads was not affected by sex reversal. However, we did find an unexpected window where MHM promoter methylation levels were very low in both males and females. This developmental window coincided with a stage of gonad development where there is a dramatic increase in expression of key testis genes in males and of key ovary genes in females. The current study raises the possibility that the non-coding RNA transcripts of MHM may affect testis and ovary differentiation by influencing sex-specific gene expression.

Female gonad morphology of small copepods Oithona similis and Microsetella norvegica

Small marine copepods, such as Oithona similis and Microsetella norvegica, form the core of polar planktonic communities. However, little is known about the gonad morphology of these species and their reproductive strategies are still debated. We studied the female genital system and reproductive traits of these common copepods collected from the White Sea during their main reproductive period (June 2012 and May 2014) and in a pre-winter season (November 2013). The applicability of the borax carmine staining method for the gonad investigation of these small species was successfully tested for the first time. We proposed the classification of O. similis gonad developmental stages that could be used to estimate the reproductive status of the population. The gonad maturation types of O. similis (Cyclopoida) and M. norvegica (Harpacticoida) are in general similar to calanoid copepods, with Pseudocalanus-type and Aetidius-type gonads, respectively [classified by Niehoff (Prog Oceanogr 74:1–47, 2007)]. Both the studied species form large oocytes at advanced maturing stage, before the hatching of the eggs carried in the sac, thereby shortening the time needed for the development of the new clutch. The percentage of fertilised O. similis females in natural population was also assessed. Many of the O. similis females were found to have spermatophores (39 % in May, 68 % in June), and almost half of them carried two or even three pairs of spermatophores. The simultaneous presence of unmated and multiple-mated adult females showed high mating opportunities and selectivity of O. similis males in some of the field populations obtained from the White Sea. Our findings do not support the “fertilisation limitation hypothesis” proposed for Oithona (Kiorboe in Limnol Oceanogr 52:1511–1522, 2007).

Histological and histochemical features of the oogenesis in the simultaneous protandric hermaphrodite shrimp Exhippolysmata oplophoroides (Decapoda: Caridea)

This study analyzes the dynamics of the vitellogenesis process in the simultaneous protandric hermaphrodite shrimp Exhippolysmata oplophoroides, based on light microscopic observations. The ovotestes of the shrimps at the different gonadal development stages were removed, fixed and submitted an usual histological procedure (HE) and histochemical techniques (Bromophenol Blue, PAS/Alcian Blue, and Von Kossa tests). The germinative cells were classified into oogonias, and oocytes in stages I–IV based on the following features: cell size, cytoplasm appearance, presence of yolk granules, lipid droplets, chorion, and chromatin patterns. In the male initial phase of the gonadal development, the ovotestes present mainly oogonia and oocytes I and II while in the functional hermaphrodite phase, oocytes III and IV predominate in the peripheral zone of the gonads. Oocytes with an atypical appearance of the cellular components indicative of reabsorption were also observed. This study showed an increasing accumulation of proteins, carbohydrates and lipids occurring as the germ cells develop, being the yolk elements deposited in a sequence, in which proteins and carbohydrates are the first to appear both by an endogenous as well as also by an exogenous origin. The presence of calcium was detected mainly in oocytes I, II and inside those in reabsorption, being posteriorly mobilized to chorion constitution and/or to hemolymph due to its role during molting. Although the similarity of the germ cells shape among the crustaceans, this first histochemical characterization of E. oplophoproides ovary increases the comprehension of oogenesis in a caridean simultaneous protandric hermaphrodite species.

Observation and establishment of gonad development stages in polyplacophorans (Mollusca): Chiton (Chiton) articulatus a case study

AbstractGonad development stages (GDS) and, subsequently, the reproductive cycle are described by performing histology of some gonad portions. In polyplacophorans, gametogenesis is not enough to define GDS; further anatomical gonad features are relevant. In most adult polyplacophorans, the gonad is a simple anatomical structure that resembles and operates as one single gonadal acinus without glandular structure. These features have gone unnoticed causing inaccurate GDS assignment and, consequently, imprecise reproductive season in polyplacophorans. Here, dissection protocols that allow extracting a compact gonad are established. Emphasizing the anatomical structure of the whole gonad and the displacement of gametes, five GDS were assigned to both sexes of Chiton (Chiton) articulatus: I‐goniogenesis, II‐development, III‐ripe, IV‐spawning, V‐rest. Tissue platelets contribute importantly to GDS assignment and even help distinguishing between males and females. Neither a randomly selected portion of gonad nor a longitudinal section are recommended because it leads to misinterpretation higher than 50% in determining GDS and besides ignores displacement of gametes. A panoramic sweep across a complete transverse‐section of each gonad was validated as the best option for establishing GDS. This new methodology was tested on several polyplacophorans species, and seems generally applicable for histological assessment of reproductive cycle and reproductive season in polyplacophorans.

Changes in tissue composition in Brazilian mojarraEugerres brasilianus(Cuvier, 1830) females at different stages of gonadal development as a starting point for development of broodstock diets

Summary Thie study evaluated the changes in proximate composition and fatty acid profile in the muscle, liver and ovarian tissues of wild-caught Brazilian mojarra Eugerres brasilianus females during sexual maturation as a starting point for the development of broodstock diets. A total of 114 females captured in the Santa Cruz Canal, Itapissuma, PE, north-eastern Brazil, from August 2012 to April 2013, were classified into four stages of gonadal development by histological analyses. Ovarian protein and total lipid levels increased with maturation, and a simultaneous decrease in liver protein and lipid levels was observed. The levels of arachidonic acid (ARA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3), docosapentaenoic acid (DPA, 22:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) also increased in the ovary as the gonadal development proceeded; they represented 96.4% of the total highly unsaturated fatty acids (HUFA) in the ovaries of fully mature females. These findings highlight the need to include protein and lipid-rich sources containing n-6 HUFA, particularly ARA, and n-3 HUFA (EPA, DPA and DHA) in the diets of Brazilian mojarra breeders.

Continuous reproduction of Sinanodonta woodiana (Lea, 1824) females: an invasive mussel species in a female-biased population

The reproductive activity of females of the Chinese pond mussel (Sinanodonta woodiana) was investigated in a European population inhabiting cooling water. The study used histological and stereological methods to determine gonad structure, changes in reproductive follicles during gametogenesis, oocyte development, glochidia structure, and brooding periods. Water in the channel of the “Dolna Odra” power plant did not freeze during the winter, and its mean annual temperature was 18.4°C. The population sex ratio was female biased (χ2 = 25.70, df = 1, P < 0.0001). Ovaries in mussels were formed by reproductive follicles. Previtellogenic and vitellogenic oocytes were attached to the follicle wall via the cytoplasmic stalk, and mature ovulated oocytes were present in the follicle lumen. Individuals with mature oocytes in gonads were present over the whole two-year study period, which indicates the continuous activity of gonads. Hooked glochidia had a larval thread. Females incubated the offspring in gill marsupia of outer demibranchs and were characterized by multiple tachytictic brooding periods. All gravid individuals presented mature and spent stages of gonadal development. The study provides the first direct information about the reproductive dynamics of this invasive species outside its original Asiatic range.

Effect of temperature and salinity on the reproductive cycle of males and females of Crassostrea virginica (Bivalvia: Ostreidae)

The American oyster, Crassostrea virginica, is one of the most important economic coastal fishery activities in Mexico. As for other bivalve molluscs, its sustainability is based on healthy populations, and additional information on current reproductive cycles, will reinforce local management strategies. The objective of this study was to evaluate the effect of temperature and salinity on the gonadal development stages in both sexes and in two size groups (40-60 mm and ≥ 61 mm) of C. virginica from Tamiahua Lagoon, Gulf of Mexico. Monthly surveys of 90 organisms were undertaken, for a yearly total of 1 080 oysters sampled from the lagoon in 2011. Both field and laboratory work used standard procedures. Our results showed that reproduction was continuous in both sexes, but some peaks of the reproductive cycle were observed along the year. Peaks registered from January to July were for gametogenesis; those of June and September were for mature individuals; and in January, February, and from September to December, for spawning/spent oysters. Maturity of females of both range sizes was positively correlated with temperature, but not for males. For spawning, spent individuals, males of sizes ≥ 61 mm were positively correlated with salinity, whereas smaller males (40-60 mm) and females of both sizes, did not show any correlation. In this study, we observed that temperature and salinity had a different effect in the reproduction of the American oyster of different sizes and sexes of Tamiahua lagoon.

Morpho-histological characteristics of gonads and reproductive index in an endemic fish species, Oxynoemacheilus persa (Heckel, 1847) (Teleostei: Nemacheilidae) from Kor River

This study presents the first details on morphological and histological characteristics of gonads, gonadal development stages and reproductive index of the Persian loach, Oxynoemacheilus persa (Heckel, 1847), an Iranian endemic species. Sampling was done from April 2010 to April 2011 using electrofishing device and a total of 196 individuals were collected. The gonads of specimens were removed, their sexes determined and then were fixed in 10% formalin solution after checking their morphology and measuring their weights, lengths and widths. Based on the size, shape and weight of the gonads, degree of occupation of the body cavity, presence or absence of ripe oocytes or milt, diameter of the oocytes in the ovary, and histological observations, five stages of sexual maturation in females and four stages in males were determined by macroscopic and microscopic criteria. The results of the gonadal stages showed that the O. persa spawns in the middle of spring and these stages were correlated to the gonado-somatic index (GSI).

Spermatozeugmata structure and dissociation of the Australian flat oyster Ostera angasi: Implications for reproductive strategy.

Variation in reproductive strategy is one of the key factors contributing to recruitment success of molluscs in different habitats. Spermcasting is a unique mode in mollusc reproduction where males produce spermatozeugmata, a radially arrayed sperm cluster wrapped by gelatinous membrane. In this study, spermatozeugmata structure and their dissociation in the Australian flat oyster Ostrea angasi were investigated to elucidate the reproductive strategy in spermcasting molluscs. The histological observation indicated that spermatogonia gradually aggregated in the gonad follicle at the early gonad development stages and developed into spermatozeugmata and became tightly packed at the advanced stages. Even though mature male and female gametes could be found in a hermaphroditic individual, the animal may prevent self-fertilization by shedding different sex gametes at different time. The O. angasi sperm are similar in size and shape to broadcasting oysters, but have one additional mitochondrion. Variations in maintaining spermatozeugmata integrity and sperm motility between individuals depended on the level of masculinity or femineity. The durations of spermatozeugmata dissociation and sperm viability were longer in males than in hermaphrodites. The unique structure and capability for spermatozeugmata to maintain the functional integrity after spawning have adaptive significance for fertilization and gamete dispersal in this species.

Reproductive periods of Lucina pectinata (BIVALVE; LUCINIDAE) in the Paranaguá Estuarine Complex, Paraná - Brazil.

The objectives of the present study is to describe the size for exploitation and gonadal maturation of L. pectinata in Peças Island in Paraná coast. Twenty two individuals were sampled every month, from an intertidal flat of the Peças River, Municipality of Guaraqueçaba, during two periods - summer/autumn and winter of the 2009. Environmental parameter data was obtained at the same time of the biological sampling: temperature, salinity and seawater transparency at the Peças River mouth. The animals' height, length, width, gross weight, wet weight of meat and dry weight of meat were measured at the lab. The gonad development stages (GDS), condition index (CI) and yield index (Y) were calculated. Sex identification was conducted by direct observation of the gonads and gametes under an optic microscope. Individuals were classified as males (M), females (F) or undetermined (U). The medium height observed was of 49.62 ± 6.84 mm. Period of more expressive gonad repletion were observed in summer when water temperature was higher. Results of GDS in both periods showed a predominance of partially filled gonad stages. This may be related with the fact that L. pectinata has intense gametogenesis activity, that is, the organisms do not have a resting interval, but go back to gonad restructuring rapidly after releasing the gametes. The continuity of the reproductive cycle of the specimens found in both studied periods could demonstrate a possible continuous reproduction of the species and a size for exploitation above 40.00 mm of height.

Molecular cloning and sexually dimorphic expression of wnt4 in olive flounder (Paralichthys olivaceus).

WNT4 (wingless-type MMTV integration site family, member 4) is regarded as a key regulator of gonad differentiation in mammalians. However, the potential role of wnt4 in teleosts during gonad differentiation and development is still unclear. The full-length cDNA sequence of wnt4 in olive flounder (Paralichthys olivaceus) was obtained using RACE (rapid amplification of cDNA ends) technique. The wnt4 ORF contains 1059 nucleotides, encoding a protein with a signal peptide domain and a wnt family domain. Expression in tissues of adult flounders was analyzed by real-time RT-PCR. The results showed that wnt4 was widely expressed in multiple tissues of flounders, and the expression level was significantly higher in ovary than in testis. Then wnt4 expression pattern was investigated during gonadal differentiation period and at gonadal development stages (I-V). The results showed the expression levels were significantly higher in testis than in ovary during gonadal differentiation. Notably, wnt4 expression had a very significant increase before testis differentiation. At gonad different developmental stages, there was no expression signal at stage I or stage II, and the expression of wnt4 was much stronger in ovary than in testis at stage III and stage IV, followed by a faint expression in stage V in both sexes. Our results imply that cloned wnt4 could be wnt4a. It is a sex-related gene and its expression pattern in gonadal differentiation period of flounder is different from that in mammalians or other teleosts. Flounder wnt4 might play more important role in testis than in ovary during gonadal differentiation.