钝缀锦蛤繁殖周期和胚胎发育

2013年8月至2014年7月,采用组织学和实验生态学方法对钝缀锦蛤(Tapes conspersus)的性腺发育、生殖周期、肥满度、胚胎和幼虫发育进行了研究。结果显示,钝缀锦蛤性腺发育以1年为1个周期,性腺发育过程可分为增殖期、生长期、成熟期、排放期和休止期5个时期;繁殖期在每年10月至翌年3月,繁殖盛期为3月、10月和11月(水温20.3~24.6℃),分批产卵。8月肥满度最高,为33.43%;4月最低,为18.31%。钝缀锦蛤卵径为70~80μm;在水温24~26℃、盐度28~32条件下,受精卵经16 h左右发育为D形幼虫;初孵D形幼虫大小为90~110μm,浮游幼虫经7~8 d培育进入附着变态期,此时壳长为210~230μm,再经4~5 d发育变态为稚贝。本研究为钝缀锦蛤的人工繁育及种质资源保护和利用提供了基础资料。     

波纹巴非蛤性腺发育周年变化与人工催产

波纹巴非蛤是福建沿海重要的经济贝类,但自然苗种资源的减少成为制约该品种养殖业发展的瓶颈。为了指导波纹巴非蛤的人工育苗,本研究以组织切片方法来确定云霄礁美海区的波纹巴非蛤的性腺周年发育,并通过人工催产实验确定最佳的催产季节。性腺组织切片观察表明波纹巴非蛤性腺发育可以分为五个时期:休止期(Ⅰ)、增殖期(Ⅱ)、生长期(Ⅲ)、成熟期(Ⅳ)及排放期(Ⅴ)。性腺周年发育表明云霄礁美海区波纹巴非蛤的性成熟率(R)7月份达到高峰(R=0.93)。在4—11月间每月进行1~2次的人工催产实验,结果表明6、7月份的催产效果最好,9、10月份的催产效果次之。结合性腺发育周年变化、人工催产实验和自然海区水温等数据,本研究得到了在本地区适时开展人工育苗生产的重要基础数据,也为波纹巴非蛤的自然资源保护提供了参考。     

南海黄鳍金枪鱼性腺发育形态观察和组织学研究

为了解南海黄鳍金枪鱼（Thunnus albacares）性腺发育规律和繁殖特征,2021年5月—2022年5月,用延绳钓在南海（17.41°N,110.61°E）采集黄鳍金枪鱼41尾,体质量0.6～35.0 kg,采用解剖和常规组织学方法,研究南海黄鳍金枪鱼的性腺发育周期和各发育时期性腺中生殖细胞的形态特征。结果表明,黄鳍金枪鱼卵母细胞发育共分6个时相,卵巢发育分为6个时期：卵原细胞增殖期、初级卵母细胞生长期、皮质液泡形成期、卵黄颗粒积累期、排卵期、退化期。黄鳍金枪鱼为分批非同步产卵类型;精巢为典型的小叶型,发育过程分为6个时期：精原细胞分化期、精原细胞增殖期、早期成熟期、中期成熟期、排精期、退化期。本文阐明了黄鳍金枪鱼性腺在不同发育时期的形态、组织结构特征及发育规律,以丰富黄鳍金枪鱼繁殖生物学基础资料,并为其人工繁育提供科学依据。     

波纹巴非蛤的性腺发育和生殖周期

根据波纹巴非蛤生殖细胞发育的规律和它们在滤泡中所占的比例,把波纹巴非蛤生殖腺发育过程分为增殖期、生长期、成熟期、排放期和休止期五个阶段。根据相对重量、鲜出肉率、干出肉率等指标的变化,并结合性腺的组织切片确定,波纹巴非蛤的性腺发育在闽南海区一年—个周期。繁殖期在5月中旬——10月下旬,但其繁殖高峰则有两次,分别在5月下旬和10月上旬。这表明波纹巴非蛤的成熟期和生殖期是相互重叠的。此外还观察到该种有雌雄同体现象。     

文蛤人工育苗技术

文蛤是我国常见的经济贝类,广泛分布在我国的各个海区。文蛤为蛤中精品,享有“天下第一鲜”的盛名, 文蛤的壳在药典上称蛤壳,可作药材治病。近几年来,由于市场的大量需求,采捕量上升,长此下去必然造成文蛤资源的破坏,因此,开展文蛤的人工育苗有着重要意义。现将文蛤的人工育苗技术简述如下： 1 文蛤的繁殖习性及发育文蛤为雌雄异体,2年性成熟,成熟的性腺包围在内脏团周围并延伸至足的基部,雌性呈奶黄色,雄性呈乳白色。卵呈圆球状,卵径为70～90μm,为沉性卵。当肥满度达到26%以上时为文蛤的繁殖盛期。繁殖期水温为20～30%,最适宜水温为25℃左右,温度越高性腺发育和成熟越快。根据性腺在内脏团的丰满度分为5期,0 期：内脏团表面透明,清晰可见,没有性腺分布,体质     

栉孔扇贝的生殖周期

本文介绍了栉孔扇贝生殖细胞的发生、生殖腺成熟度和生殖周期的研究结果。作者把栉孔扇贝的卵细胞发生分为卵原细胞期、无卵黄期、卵黄形成前期、卵黄形成后期和成熟期五个阶段；把精子的发生过程分为精原细胞期、初级精母细胞期、次级精母细胞期、精细胞期和精子期五个阶段。对于栉孔扇贝生殖腺的发育过程，作者根据生殖细胞在滤泡中所占的比例，把它分成增殖期、生长期、成熟期、生殖期和休止期五个阶段。栉孔扇贝的性腺发育在青岛海区为一年一个周期，但其繁殖高峰则有二次，这表明栉孔扇贝的成熟期和生殖期二者是相互重叠的。此外，作者也观察到了栉孔扇贝的雌雄同体现象。     

熊本牡蛎三倍体与二倍体性腺发育特征比较

为了评估三倍体熊本牡蛎(Crassostrea sikamea)的繁殖潜力, 采用细胞松弛素 B 诱导了熊本牡蛎三倍体, 比较了 60 日龄(2016 年 8 月)~450 日龄(2017 年 9 月)三倍体与二倍体性腺发育特点, 分析了性腺发育与繁殖周期的相关性。研究结果表明, 熊本牡蛎三倍体与二倍体性腺发育均可分为形成期、增殖期、成熟期、排放期和耗尽期 5 个时期; 在一个繁殖周期内 22%的三倍体性腺可发育至成熟期, 但与二倍体相比, 三倍体成熟性腺的滤泡小、结缔组织丰富; 三倍体与二倍体性腺发育周期同步, 繁殖季节均位于 3—9 月, 繁殖期较长; 150 日龄(2016 年 10 月)三倍体与二倍体中发育的性腺(包括增殖期、成熟期、排放期、耗尽期)分别占 70%与 90%, 210 日龄(2017 年 1 月)减小至 3%与 18%, 之后性腺再次发育, 分别在 360 日龄(2017 年 6 月)和 450 日龄(2017 年 9 月)成熟期性腺比例达到最大值(40%和 90%)。三倍体与二倍体雌雄比分别为 1.35 : 1 和 0.95 : 1, 三倍体性比显著偏离 1 : 1 (P<0.01)。性腺成熟期三倍体与二倍体平均卵径分别为(44.30±6.88) μm 与(37.76±5.76) μm, 三倍体卵径比二倍体大 17.33% (P< 0.05)。本研究可为熊本牡蛎三倍体和二倍体繁育提供参考依据。     

方格星虫繁殖生物学研究

通过观察体腔生殖细胞发育的季节变化，研究广西海区方格星虫繁殖周期。研究样本采自北海市大冠沙至白虎头海区3个站点，1999年1月至2000年2月每月定期采集。观察结果表明，方格星虫雌雄异体；体腔内的生殖细胞最初成团附着在具有运动能力的滋养细胞上，卵原细胞经过细胞增殖期（1-2μm）、细胞质生长期（3-30μm）、滤泡膜形成期（30-70μm）、胶质膜形成期（70-160μm）和成熟期(≥160μm）5个发育时期；精原细胞的发育经过细胞增殖期、细胞生长期、细胞分化期和成熟期4个发育时期。方格星虫体腔全年都有生殖细胞存在，卵细胞分期成熟，分批产卵。广西海区方格星虫繁殖期于每年4-9月，繁殖盛期为5-8月。     

偏顶蛤胚胎和幼虫发育及温度对其浮游幼虫生长和发育的影响

在室内条件下,人工诱导偏顶蛤(Modiolus modiolus)产卵并在显微镜下对其胚胎和浮游期幼虫的形态进行连续观察和拍照,并采用实验生态学的方法,研究温度对其浮游期幼虫生长和发育的影响。结果显示,偏顶蛤亲贝人工催产时,以流水刺激4 h,阴干12 h为宜。偏顶蛤卵呈圆形或卵圆形,沉性卵,卵径为(82.6±3.2)μm,精子鞭毛型,全长约50μm。在水温19~21℃下,偏顶蛤受精卵发育至D形幼虫(壳长104.0μm±4.3μm)、匍匐幼虫(壳长255.8μm±15.0μm)和早期稚贝(壳长329.1μm±5.8μm)分别历时20.5 h、20 d和36 d。水温是影响偏顶蛤幼虫生长和发育的主要因素之一,幼虫适宜水温为15~20℃,15℃组幼虫畸形率显著低于20℃组,生长率20℃组最高达5.4μm/d;水温25℃和30℃下,幼虫畸形率均显著高于15℃组和20℃组,并分别在第6天和第4天全部死亡。相对于高温而言,偏顶蛤幼虫对低温的耐受能力更强。本文旨在为偏顶蛤繁殖生物学和苗种繁育技术提供基础资料。     

养殖光倒刺鲃精巢发育的研究

经激素处理和生态调控的光倒刺鲃,能够完成精巢发育的全过程;按照形态学特征将精巢的发育分为6个时期,依组织学特点将精巢的变化分为6个时期:即原始生殖细胞期,增殖期到原始生殖细胞期早期生长期,生长早期,生长晚期,成熟期,排空期。大多数雄体在3～4龄性腺发育成熟,繁殖期为4～9月。     

Association between the interannual variation in the oceanic environment and catch rates of bigeye tuna (Thunnus obesus) in the Atlantic Ocean

The environmental processes associated with variability in the catch rates of bigeye tuna in the Atlantic Ocean are largely unexplored. This study used generalized additive models (GAMs) fitted to Taiwanese longline fishery data from 1990 to 2009 and investigated the association between environmental variables and catch rates to identify the processes influencing bigeye tuna distribution in the Atlantic Ocean. The present findings reveal that the year (temporal factor), latitude and longitude (spatial factors), and major regular longline target species of albacore catches are significant for the standardization of bigeye tuna catch rates in the Atlantic Ocean. The standardized catch rates and distribution of bigeye tuna were found to be related to environmental and climatic variation. The model selection processes showed that the selected GAMs explained 70% of the cumulative deviance in the entire Atlantic Ocean. Regarding environmental factors, the depth of the 20 degree isotherm (D20) substantially contributed to the explained deviance; other important factors were sea surface temperature (SST) and sea surface height deviation (SSHD). The potential fishing grounds were observed with SSTs of 22–28°C, a D20 shallower than 150 m and negative SSHDs in the Atlantic Ocean. The higher predicted catch rates were increased in the positive northern tropical Atlantic and negative North Atlantic Oscillation events with a higher SST and shallow D20, suggesting that climatic oscillations affect the population abundance and distribution of bigeye tuna.     

Rare serotype occurrence and PFGE genotypic diversity of Streptococcus agalactiae isolated from tilapia in China

Previously, we reported 10 PEGE types of 85 tilapia Streptococcus agalactiae(GBS), which shifted from Streptococcus iniae in China, by using PEGE method. Presently, larger and more representative tilapia GBS were isolated, for the ?rst time in China, to characterize their serotypes and genetic diversities more precisely than had done before. 168 GBS strains were distributed in ?ve provinces of China, in which Guangdong, Guangxi and Hainan were the major ones, holding36.9%(62/168), 37.5%(63/168) and 19.6%(33/168), respectively. Serotypes, Ia, Ib and III, were observed in these strains and the most predominant one was Ia(95.2%), which mainly distributed in Guangdong, Guangxi and Hainan. Ia initially occurred in 2009, it shoot up to 32.1% in 2010,but decreased to 16.1% in 2011 before went up to 45.2% in 2012. Ib sporadically occurred during2007–2011, III onlyoccurred in 2012. 14 different PFGE types, including 4 new types(N, O,P and Q), were observed, in which B, D, F and G were the predominant types, holding 83.9%(141/168) of the total GBS strains. Ia corresponded to 11 PFGE types(A–H, N–P), in which type D predominated(51%). Ib represented 3 genotypes(I, J and Q) and III harbored only 2genotypes(N and F). Type N and Fsynchronously presented in Ia and III. In summary, the genetic diversity of tilapia GBS varied by serotypes and changed with geographical locations and years.Although Iastillpredominated, new rareserotypeIII alreadyoccurred in China.     

Growth performance,digestive enzyme activity and immune response of Japanese sea bass,Lateolabrax japonicus fed with fructooligosaccharide

In this experiment, a feeding trial was performed to determine the effects of fructooligosaccharide (FOS) on growth performance, digestive enzyme activity and immune response of Japanese sea bass, Lateolabrax japonicus juveniles (initial weight 38.3 ± 0.5 g), and the fish were examined following feeding with six levels of FOS (0, 0.5, 1, 2, 4 and 6 g/kg) for 28 days. Significant enhancement of weight gain (WG) and specific growth rate (SGR) was found in fish fed 1 g/kg FOS incorporated diets (p < .05), while the feed conversion ratio (FCR) in the 1, 2 g/kg FOS groups reduced significantly compared with the control (p < .05). Besides, the crude lipid in the 4, 6 g/kg FOS groups increased significantly compared with the control (p < .05). On the other hand, the erepsin and lipase activities significantly elevated in intestine of fish fed 2 g/kg FOS (p < .05) and the lysozyme activity in serum of fish fed 2 g/kg FOS were significantly higher than that in the control (p < .05). Moreover, the alkaline phosphatase activities in serum of fish fed 0.5, 1, 2 g/kg FOS were significantly higher than in control (p < .05). Regression analysis showed that the relationships between dietary FOS levels and either SGR, FCR, erepsin or lysozyme activities were best expressed by regression equations, and the optimal inclusion levels are 1.37, 1.80, 3.06, 3.11, 1.93 and 1.80 g/kg for SGR, FCR, erepsin, lipase, lysozyme and total superoxide dismutase activities, respectively. Overall, this study revealed that FOS incorporated diets could beneficial for L. japonicus culture in terms of increasing the growth, digestion and immune activities. Under the present experimental condition, the optimal supplementary level of FOS in the diet of L. japonicus is 1–3 g/kg.     

Evaluation of a Fast Method Based on the Presence of Two Restriction Sites in the Mitochondrial ND5 (mt ND5) Gene for the Identification of Scomber Species

The purpose of this work was to evaluate the suitability of a method based on the presence of two restriction sites (for Hae III and Hindf I) in the mitochondrial NADH dehydrogenase subunit 5 (mt ND5) gene to identify Scomber species. The evaluation was performed on 144 reference and market samples by sequencing of the entire 505-bp fragment of the mt ND5 gene and of a 464-bp fragment of the Kocher fragment of the cytochrome b gene (mt Cytb). Sequence analysis of any of the two fragments allows the identification of each of the four Scomber species, but S. japonicus and S. colias had the same restriction sites at the ND5 amplicon and would not have been differentiated by this analysis. Similarly, loss of the Hae III site in some S. scombrus individuals would have misidentified them as not being Scomber. All the market products were correctly labeled except one acquired in Spain labeled as originating in the Atlantic and containing S. japonicus.     

Purification and partial characterization of GtHs (cfLH and cfFSH) from Indian walking catfish (Clarias batrachus) (L.) and development of a homologous ELISA for cfLH

Two gonadotropins (GtH; Qa and Qb) were purified by gel filtration and ion exchange chromatography from the pituitaries of Indian walking catfish (Clarias batrachus). The presence of GtH during purification was assessed by in vitro oocyte maturation and in vivo steroidogenic activity, and their identities were determined by elution profiles, molecular weight, biological activities and yield. The molecular weights of Qa and Qb were 37 and 42 kDa, respectively, and composed of distinct subunits (Qa: 20 and 14 kDa and Qb: 26 and 18 kDa). Polyclonal antibodies raised against Qa immunostained Qa, Qb and pituitary GtH cells. A competitive Qa‐ELISA was developed whose sensitivity was 6.25 ng mL^?1 (1.25 ng well^?1) with intra‐ (3.5%) and inter‐ (12.4%) assay coefficients of variation. Displacement curves parallel to the standard were obtained with plasma and pituitary extracts of catfish, Qb and carp GtHII. The assay was validated by measuring the plasma Qa levels after LHRH treatment and in relation to ovarian growth in the female catfish during different reproductive phases. Based on the results, Qa and Qb corresponded to fish LH and FSH respectively. The findings will increase the knowledge of the mechanisms controlling fish reproduction and identification of sensitive phases in fish in captivity for hormonal manipulation.     

Controlled infection of Poecilia reticulata Peters (guppy) with Tetrahymena by immersion and intraperitoneal injection

Tetrahymena is a protozoan parasite, which infects guppy, Poecilia reticulata Peters, and causes substantial economical losses in commercial farms worldwide. Studies of guppy infected by Tetrahymena require standardized infection protocols. The LD50 for Tetrahymena infection of guppies by intraperitoneal (IP) injection was calibrated, and the level obtained was 946 parasites per fish. Guppy infection with Tetrahymena by immersion, imitating the natural route of infection via the integument, was studied under normal or stress conditions. Exposure to cold and netting (CNI) and to cold only (CI) followed by immersion exposure to 10 000 Tetrahymena per mL resulted in 22.5% and 19.2% mortality, respectively, as compared to 14.2% and 10% in groups that were netted only (NI) or non‐stressed (I). Histopathology revealed that immersion infection resulted in a systemic infection. Lysozyme levels, measured 3 weeks after infection, were significantly higher in the CNI group (288 μg per mg protein) compared with CI‐, NI‐ and I‐treated groups (94.5, 64 and 62.3 μg mg^?1, respectively). There was no evident parasite immobilization activity in body homogenates, suggesting no development of acquired immunity. Re‐infection by IP injection revealed no increase in protection in any of the treatment groups, mortality range of 56.3–75%, higher than in the non‐exposed control (40.6% mortality).     

The optimal dietary protein level of juvenile silver sillago Sillago sihama at three dietary lipid levels

A 5 × 3 factorial growth trial was conducted to evaluate optimal dietary protein and lipid levels (dietary protein level, DP; dietary lipid level, DL) for juvenile Sillago sihama (S. sihama) (2.0 ± 0.02 g, initial weight). Fish were fed 15 diets containing 5 DPs (350, 400, 450, 500 and 550 g/kg) and 3 DLs (60, 90 and 120 g/kg) for 8 weeks. The interaction between proteins and lipids significantly influenced the feed conversion ratio, condition factor, body composition, antioxidant indices and lipase activity (p < .05). DP 450 g/kg showed the highest average final body weight. DPs 500 and 550 g/kg significantly decreased the protein efficiency ratio (p < .05). DL 120 g/kg showed the highest percentage weight gain. The low feed conversion ratio was found in diets P45L12, P55L9 and P55L12. Diet P45L12 showed high superoxide dismutase activities. DP 450 g/kg showed the lowest average malondialdehyde content. Lipase activity was increased by increasing DP (p < .05) with a fall at DP 550 g/kg. Under the present experimental conditions, the optimal DP for S. sihama was 450 g/kg under the DL 120 g/kg.     

Involvement of gonadal steroids in final oocyte maturation of white perch (Morone americana) and white bass (M. chrysops): in vivo and in vitro studies

Plasma estradiol-17 (E₂), testosterone (T), 17,20-dihydroxy-4-pregnen-3-one (DHP) and 17,20,21-tri-hydroxy-4-pregnen-3-one (20-S) levels were measured by radioimmunoassay (RIA) in white perch (Morone americana) and white bass (M. chrysops) that were induced to undergo final oocyte maturation (FOM) with human chorionic gonadotropin (hCG). Plasma DHP levels increased in females of both species in association with oocyte germinal vesicle migration (GVM) and germinal vesicle breakdown (GVBD) and decreased thereafter. Plasma 20-S levels also increased with oocyte GVM in white bass, but were several-fold lower than DHP levels. Circulating E₂ and T levels were greatest during GVM and GVBD in both species and decreased to low levels during oocyte hydration and ovulation. Follicles from white perch and white bass which received a priming injection of hCG in vivo, produced both DHP and 20-S in vitro after exposure to hCG and their oocytes underwent GVBD. Ovarian incubates from unprimed fish of either species produced only E₂ and T and their oocytes did not complete GVBD. Oocytes from unprimed bass, but not perch, matured when follicles were exposed to hCG in vitro. Both trilostane and cycloheximide blocked in vitro production of DHP and 20-S and oocyte GVBD by white perch follices. DHP and 20-S were equipotent inducers of FOM in the GVBD bioassay. None of several other structurally-related steroids tested were effective within a physiological range of concentrations. These results indicate a role for DHP and 20-S in the control of FOM in white perch and white bass.