Cloning of estrogen receptor-β cDNA of common Japanese conger Conger myriaster and expression of the gene during oocyte development

ABSTRACT:   Estrogen receptor (ER) cDNA was cloned from the liver of common Japanese conger Conger myriaster . Common Japanese conger ER cDNA contains 2543 nucleotides including an open reading frame that encodes 596 amino acids, with a molecular weight of 66.1 kDa. The deduced amino-acid sequence of the common Japanese conger ER shares 85% identity with that of eel Anguilla japonica ER-β, and 39–46% and 53–59% identity with the deduced sequences of ER-α and ER-β of other species, respectively. In a phylogenetic analysis, the common Japanese conger ER was found to cluster with the ER-β of other species. The common Japanese conger ER-β also has six domains (A–F), which are conserved in the nuclear receptor superfamily. The amino-acid sequences in the C and E domains were highly conserved between common Japanese conger ER-β and other ER. However, the other domains showed low homology. In the female common Japanese conger, ER-β mRNA was highly expressed in the liver and pituitary gland. The expression levels of the ER-β gene increased from the oil droplet stage to the primary yolk globule stage and were maintained until the migratory nucleus stage.     

Reproductive cycle in reared male common Japanese conger, Conger myriaster

Annual changes in gonadal histology, gonadosomatic index (GSI), and plasma 11-ketotestosterone (11KT) levels were investigated in reared male common Japanese congers, Conger myriaster. Young fish, 20–30 cm in total length and around 20 g in body weight, caught in November 1996 (group 1) and in September 1999 (group 2) were reared for 3 years in seawater at temperatures ranging from 10 to 20 °C.

In most fish, only spermatogonia occupied the testes for 1 year and a few months after capture. Spermatocytes appeared in February, and both spermatids and spermatozoa appeared in March, in 1998 for group 1 and in 2001 for group 2. Spermiation was observed from May to September and reduction in testis was observed after October in both groups. GSI and plasma 11KT levels changed with progression of spermatogenesis. Although GSI was less than 1.0 and the plasma 11KT level less than 1.0 ng/ml, in the first year in most fish, both increased in the second year of rearing. GSI peaked in June 1998 (5.3±3.0; mean±standard deviation) in group 1 and May 2001 (2.3±1.3) in group 2, and bottomed in October (0.3±0.1) in both groups. Plasma 11KT levels peaked in March 1998 (5.8±1.9 ng/ml) in group 1 and May 2001 (4.4±2.4 ng/ml) in group 2, and bottomed in August in group 1 and September in group 2 (around 0.1 ng/ml in both groups). Spermatogenesis and changes in GSI and plasma 11KT levels were repeated the following year in both groups.

These observations indicate that males have an annual reproductive cycle under rearing conditions. It is possible that wild male common Japanese congers also have multiple spawning seasons in their lives.     

海州湾星康吉鳗的摄食生态特征

根据2011年3—12月在海州湾及其邻近海域进行的5个航次的底拖网调查,通过分析516尾星康吉鳗(Conger myriaster)的胃含物样品,对其食物组成、食性类型、摄食强度、营养生态位以及营养级等摄食生态特征进行了初步研究。结果表明,星康吉鳗摄食的饵料种类有40余种,鱼类、虾类和头足类是其最主要的3种饵料类群,优势饵料生物有尖海龙(Syngnathus acus)、矛尾虾虎鱼(Chaeturichthys stigmatias)、鲜明鼓虾(Alpheus distinguendus)、枪乌贼(Loligo sp.)等。星康吉鳗的食性类型以底栖动物和游泳动物食性为主,其食物组成存在明显的季节变化和肛长变化,除在4个季节均摄食大量的鱼类和虾类外,秋季还摄食大量头足类。不同肛长组星康吉鳗摄食的主要饵料种类存在明显差异:肛长小于70 mm的星康吉鳗主要摄食枪乌贼,70~99 mm的星康吉鳗主要摄食绯(Callionymus beniteguri)和鲜明鼓虾,大于100 mm的星康吉鳗则主要以枪乌贼、尖海龙(Syngnathus acus)和鲜明鼓虾为食。星康吉鳗的空胃率和平均胃饱满指数存在明显的季节变化,空胃率夏季最低,春季最高;平均胃饱满指数春季最低,秋季最高。星康吉鳗的营养级为4.17,表明其在海州湾食物网中处于较高的营养位置。本研究发现,海州湾星康吉鳗的摄食随季节和肛长的变化,主要与其栖息海域中优势饵料生物的种类组成和丰度有关,因此,通过定期监测星康吉鳗的摄食可间接了解基础饵料生物种类和数量的变动情况,同时也为食物网的构建和生态系统营养动力学的研究提供基础资料。     

Development of embryos and larvae in the common Japanese conger Conger myriaster

Development of embryos and larvae in the common Japanese conger Conger myriaster was observed after artificial fertilization. Eggs were obtained from females matured artificially by hormone injections and milt was obtained from males matured naturally. Fertilized eggs were kept in seawater at 12–14°C. The first cleavage occurred at 4 h, epiboly began at 24 h, the embryonic body was formed at 38 h and hatching occurred at 84 h after insemination. Newly hatched larvae were approximately 2.5 mm (total length) and similar to those of Anguilla japonica in terms of external features. The mouth and anus opened on the 7th day after hatching. Pigments began to appear at the tip of the tail on the 10th day. The total length of the larvae reached approximately 8 mm on the 11th day. Eye pigmentation began on the 14th day. One larva lived for 19 days without food.     

投喂频率对工厂化循环水养殖星康吉鳗生长、生理指标及其水质的影响

本研究采用生理学和实验生态学方法探究了工厂化循环水养殖模式下,不同投喂频率对星康吉鳗(Conger myriaster)生长、生理指标以及水质因子的影响。选用初始体重为(150.64±5.43) g的星康吉鳗为研究对象,实验共设2组,分别为1次/天(T1组)、2次/天(T2组),每组3个重复,实验周期为70d。实验每14d检测各养殖池实验鱼平均体重和循环水系统水质指标;实验结束时,采集星康吉鳗血液、组织相关样品,用于生长、生理指标的测定与分析。结果显示,T2组终末体重(FBW)、终末体长(FBL)、增重率(WGR)、特定生长率(SGR)显著高于T1组(P<0.05),T1组饲料系数(FCR)显著高于T2组(P<0.05)。T1组血清丙二醛(MDA)显著高于T2组(P<0.05),T2组肝脏谷草转氨酶(AST)、肝脏谷丙转氨酶(ALT)、肠道胰蛋白酶(TPS)显著高于T1组(P<0.05)。T1组、T2组出口水NH₄⁺-N、NO₂^--N 24 h变化中分别有1处(24:00)和...     

Annual changes in ovarian development and plasma estradiol-17β level in reared female common Japanese conger, <Emphasis Type="Italic">Conger myriaster</Emphasis>

ABSTRACT:   Annual changes in the gonadosomatic index (GSI), oocyte diameter, gonadal histology and plasma estradiol-17β (E₂) levels were investigated in female common Japanese conger Conger myriaster in captivity. Juveniles were caught in September 1999 and reared in seawater at temperatures ranging from 10–20°C for 3 years. All fish were immature when captured in September 1999. GSI and oocyte diameter increased from October 2000, peaked between summer and autumn 2001, and bottomed-out in winter 2001. Plasma E₂ level also increased from October 2000, but remained high. The ovarian developmental stage was at the peri-nucleolus stage or the oil droplet stage until September 2000. Vitellogenesis started in October 2000 and oocytes progressed to the tertiary yolk globule stage by summer 2001. However, vitellogenic oocytes regressed in all females after autumn 2001. The neogenetic oocytes began to increase after November 2001 and ovarian development progressed in 2002 as they did in 2001, although maximum GSI in 2002 was half its 2001 value. These data indicate that ovarian development in the common Japanese conger has an annual periodicity, and that these congers may be able to spawn in multiple years under rearing condition.     

Evidence for genetic differentiation in the european conger eel Conger conger based on mitochondrial DNA analysis

ABSTRACT:   The European conger eel Conger conger is an important marine benthic fish in the North-East Atlantic and represents a valuable fishery resource. However, little is known about its reproductive biology. In an attempt to gain a better understanding of the conger eel population structure, mitochondrial DNA (mtDNA) sequences were examined. A region with 432 bp of the control region of the mtDNA was sequenced from 40 individuals from six different locations around the central and eastern North Atlantic Ocean. Thirty variable positions defined 28 distinct haplotypes. The average sequence difference within samples (1.3–4.2%) was comparable to those between samples (1.4–3.6%). MtDNA sequence-based statistical tests showed significant geographic differentiation between some local population samples, suggesting that the conger eel does not comprise a single panmictic population. However, given our sample sizes, these preliminary results should be interpreted with caution and more individuals from more sites, including the Mediterranean Sea, should be analyzed in detail. The genetic variability detected in this study is an initial step to elucidate the genetic background of the conger eel population structure.     

Size selectivity of escape holes in conger tube traps for inshore hagfish <Emphasis Type="Italic">Eptatretus burgeri</Emphasis> and white-spotted conger <Emphasis Type="Italic">Conger myriaster</Emphasis> in Tokyo Bay

ABSTRACT:   In Tokyo Bay, conger tube-trap fishers voluntarily deployed escape holes of at least 13 mm diameter to reduce the by-catch of young conger smaller than the marketable size of 35 cm total length. Comparative fishing experiments in Tokyo Bay were carried out using tube traps with seven hole diameters (3, 9, 13.5, 14, 15, 17, and 19 mm), to obtain the size-selectivity of the escape-hole size for inshore hagfish Eptatretus burgeri and white-spotted conger Conger myriaster . On the assumption of the geometrical similarity in the combination of body g and hole perimeter m at a given retention probability, a single master curve s ( R ) = exp(−13.52 + 11.31 R )/(1 + exp [−13.52 + 11.31 R ]) was estimated for the two species in terms of relative R  =  g / m using the Share Each LEngth's Catch Total (SELECT) process based on a multinomial distribution. Almost all conger and hagfish with a girth equivalent to the hole perimeter were able to pass through the hole. Thus, the two species have a high ability to escape through a narrow space by squeezing the body through the hole in the rigid PVC tube. Optimum escape-hole size is discussed from several objectives for conger tube-trap fishery management, e.g. reduction of hagfish by-catch. This study also specifies the conditions for pooling data when fishing experiments using more than two fishing gears are replicated.     

山东南部近海秋、冬季星康吉鳗分布与环境因子的关系

根据2016年10月和2017年1月在山东半岛南部海域秋、冬2个航次获取的渔业资源与栖息环境调查数据,分析了星康吉鳗(Conger myriaster)的时空分布特征。运用广义可加模型研究了星康吉鳗数量分布与季节、水深、底层盐度和底层水温等影响因子间的关系。结果表明,该海域星康吉鳗的数量分布有明显的季节变化,秋季的渔获率高于冬季,且分布范围更广。星康吉鳗在近岸海域渔获率较高,分布相对均匀,远岸海域渔获率较低,分布不均匀。广义可加模型显示,对星康吉鳗分布影响显著的环境因子为水深和底层水温(P0.05),其中水深的影响最为明显。星康吉鳗渔获率随水深的增大呈现先增加后减少再增加的趋势,在水深30~40 m处渔获率较高。星康吉鳗渔获率随水温的升高呈现先增加再减少的趋势,最适水温约为10℃。山东南部近海星康吉鳗的空间分布与其洄游习性、黄海暖流的季节变化等引起的海洋环境因子的变动有关。     

珠江水系大眼鳜的繁殖生物学

为了研究大眼鳜（Siniperca kneri）的繁殖生物学,对珠江水系的322尾大眼鳜性成熟样本进行了生物学指标测量。根据性腺成熟系数周年变化情况和成熟度周年分布,可以推断大眼鳜的生殖季节为4-8月份,产卵旺季为5-6月份。绝对怀卵量随体长、体重、年龄的增加而增加,在11036～106022粒之间,相对怀卵量则不随体长、体重、年龄的变化而变化,而是保持在每克100粒左右。在水温24～25℃时,受精卵经过69h23min孵化出膜。     

鲤脑垂体和HCG诱导雌性日本鳗鲡性腺成熟过程中血清生化成分的变化

使用鲤脑垂体和HCG对雌性日本鳗鲡人工催熟,用临床医学检验方法,测定分析了雌性日本鳗鲡卵巢发育过程中,血清总蛋白(TP)、血清甘油三脂(TG)、血清胆固醇(TC)、血糖(Glu)、血钙(Ca)和血清无机磷(P)6项生化指标的水平及变化趋势,并与对应的不同卵巢发育阶段的性腺成熟系数(GSI)进行比较分析。结果表明,84d的注射过程中,实验组的性腺逐渐成熟,GSI显著升高,第12针时达到46.32%±1.75%;而对照组性腺GSI一直在2.42%±0.18%。实验组和对照组血清TP水平相对平稳,各组变化无显著差异(P>0.05)。实验组和对照组血脂在56d前差异显著(P<0.05):实验组血清TG,TC一直维持较高水平,平均分别为(12.67±2.83)mmol/L和(15.54±3.01)mmol/L;对照组TG和TC一直下降且水平较低,平均分别为(6.33±4.14)mmol/L和(8.53±3.30)mmol/L。实验组和对照组血清Glu均在实验初的较低水平基础上持续上升。相关分析表明,实验组血清TG与GSI水平极显著负相关(r=0.732,n=6,P<0.01)。实验组血清Ca与GSI(r=0.961,n=6,P<0.01),血清P与GSI(r=0.775,n=6,P<0.01)都呈现出极显著的相关性:血清Ca和P在28d后持续上升,GSI逐渐增大。对照组中的血清Ca和P水平则一直维持在一个较低的水平。研究结果表明:雌性日本鳗鲡卵巢发育与其脂类代谢密切相关,无机离子(Ca,P)在此过程中起到重要作用。利用繁殖鱼体营养代谢特点,检测日本鳗鲡血脂或血清Ca和P水平,可成为初步判断雌性日本鳗鲡发育情况的新方法。     

Discovery of a spawning area of the common Japanese conger <Emphasis Type="Italic">Conger myriaster</Emphasis> along the Kyushu-Palau Ridge in the western North Pacific

The common Japanese conger Conger myriaster is an important commercial coastal fisheries species in East Asia, but its spawning area has not been determined. A larval sampling survey was conducted in September 2008 along 136°E between 13°N and 22°N, which roughly followed the Kyushu-Palau Ridge in the western North Pacific. Twenty larval specimens were confirmed to be C. myriaster using DNA analysis. Two were newly hatched larvae (preleptocephali) 5.8 and 7.8 mm in total length (TL), which were caught at 17°N. The 5.8 mm TL larva was estimated to be 3–4 days after hatching, the youngest preleptocephalus (i.e., the earliest stage) of this species ever collected. Eighteen other leptocephali were caught at 18°N and 21°N, and these ranged from 18.6 to 40.0 mm TL. Based on these collections, we discerned that there is a spawning area of C. myriaster in the area along the Kyushu-Palau Ridge approximately 380 km south of Okinotorishima Island. Similar to the Japanese eel spawning area along the West Mariana Ridge, the Kyushu-Palau Ridge may play an important role as a landmark of the spawning area. The discovery of this offshore spawning area should lead us to a better understanding of the recruitment mechanisms of C. myriaster, and help to facilitate future international management efforts.     

Maturation and spawning of the small penaeid shrimp Metapenaeopsis dalei in Tosa Bay, Pacific coast of southern Japan

SUMMARY: Seasonal changes in the percentage of mature female Metapenaeopsis dalei were studied histologically, and the annual cycle of maturation and spawning of this species was discussed. Specimens were collected at night by a beam trawler in Tosa Bay (33°N, 133°E) during the period from April 1995 to March 1996. All individuals had a gonado somatic index [ GSI = 100 (gonado weight/body weight)] of higher than 8, and 66.7% of those individuals with a GSI of 6–8 had oocytes in the late phase of the prematuration stage after germinal vesicle shrinking and migrating to the margin of the oocyte or had oocytes in the maturation stage. Such individuals with developed oocytes appeared in April, June, July, August, October, November and March. Individuals with a GSI above 6 appeared throughout the year, except during September and February. Individuals with ovulated oocytes were sampled in March when the water temperature near the bottom depths was lowest (15.4°C) during the year, being similar to February (15.1°C). These facts indicate that maturation occurs all year-round and suggests that spawning in the Metapenaeopsis dalei population in Tosa Bay occurs all year-round. This is the first report of year-round maturation in penaeid shrimps in Japanese waters.     

Effect of probiotic on reproductive performance in female livebearing ornamental fish

A probiotic bacterial strain, Bacillus subtilis, isolated from the intestine of Cirrhinus mrigala (Hamilton), was incorporated in fish feed at four different concentrations (5 × 10⁸ cells g⁻², 5 × 10⁷ cells g⁻², 5 × 10⁶cells g⁻¹ and 5 × 10⁵ cells g⁻¹) and fed to four species of livebearing ornamental fish, Poecilia reticulata (Peters), Poecilia sphenops (Valenciennes), Xiphophorus helleri (Heckel) and Xiphophorus maculatus (Gunther) for one year duration to observe the effect of dietary probiotic supplementation on their reproductive performance. Sixty virgin females of each species were stocked separately in circular FRP tanks (350 L) and fed diets with varying levels of probiotic cells and control feed. Broodstock performance was evaluated based on gonadosomatic index (GSI), fecundity and fry production of female broodstock. The results showed that supplementation of feed with probiotics increased significantly (P<0.05) the GSI, fecundity and fry production of spawning females and length and weight of fry in all the four species of fish. The number of dead and deformed fry were also significantly lower (P<0.05) in fish fed with the probiotic feeds. The use of higher concentration of the probiont in diet did not always lead to significantly improved reproductive performance of the spawners. Collectively, this study showed that female livebearers benefit from inclusion of probiotics in diet during their reproductive stages.