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.     

Oogenesis in the common Japanese conger Conger myriaster

ABSTRACT:    We investigated the process and characteristics of oogenesis in the common Japanese conger Conger myriaster . Young fish caught in November 1996 were reared for use in this experiment. Fish were sampled monthly from December 1997 to August 1998. Some were injected with human chorionic gonadotropin to stimulate ovarian maturation from May to August 1998. Oocytes from the chromatin nucleolus stage to the secondary yolk globule stage were obtained from non-hormone-treated fish; those of more advanced stages were obtained from hormone-treated ones. We divided oocyte development into eight stages from the chromatin nucleolus stage to the maturation stage. The yolk vesicle stage was not separated because yolk vesicles began to appear just after appearance of yolk globules. Oocyte, oil droplet, yolk globule and nucleus diameters all increased concomitant with oocyte development. Oil droplet and yolk globule diameters increased remarkably at the maturation stage. However, zona radiata thickness peaked at the secondary yolk globule stage, decreasing gradually thereafter. Increased gonadosomatic index was related to oocyte development as found in European and Japanese eels receiving hormone treatment to mature. The present study is the first report describing oogenesis characteristics in congrid eels. It indicates that oogenesis is almost identical to that of other anguillid eels.     

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.     

Development of the common dentex (Dentex dentex) eggs in relation to temperature

Embryonic development of common dentex (Dentex dentex) was investigated at nine different constant water temperatures (8°C, 10°C, 12°C, 14°C, 16°C, 18°C, 20°C, 22°C and 24°C). The observed effects were compared using of regression analysis. Constant water temperatures between 12°C and 18°C were found to support successful embryonic development. A negative relationship between the rate of embryonic development and incubation temperature was observed. While embryonic development was completed within this range (12°C–18°C), there was no cell division at water temperatures of 8°C and 24°C. Total mortalities were observed at the 128 cleavage stage at a temperature of 10°C, and after the beginning of gastrulation at 20°C and 22°C.     

半滑舌鳎胚胎发育及稚鱼变态过程观察

利用显微镜对半滑舌鳎胚胎发育及稚鱼变态过程进行连续观察,对各个时期的发育时间进行了记录,并对不同时期的特征用进行了拍摄。结果表明：半滑舌鳎成熟卵子呈球形,为多油球浮性卵。受精卵培养在水温21．6—22．8℃,pH值7．0～8．2。盐度30的海水中,历时39h仔鱼孵出。与其他硬骨鱼类基本相似,半滑舌鳎胚胎发育属于盘状卵裂,发育过程可分为：受精卵、卵裂期、囊胚期、原肠期、神经胚期、器官分化期、出膜期和初孵仔鱼。仔鱼孵化出膜进入胚后发育阶段,之后进入变态期,向成鱼转化。与牙鲆、大菱鲆等鲆鲽鱼类不同,半滑舌鳎稚鱼变态初期是在头顶两眼前上方形成一个横裂,右眼由此横列穿过,最终到达身体左侧,此后横裂逐渐愈合,变态完成,该过程历时3-4d,其形成机制有待进一步深入研究。     

Development of microparticle diets for Japanese flounder Paralichthys olivaceus larvae

ABSTRACT:   Two newly designed microparticle diets (MD), with two kinds of peptide (C700 and C800) as a protein source were developed. Microparticle diet Q (MD-Q) contained C700 (molecular weight ∼30 000 Da) and C800 (molecular weight 1000–2000 Da); in contrast, microparticle diet T (MD-T) contained C700 only. Two separate trials, representing larvae from different hatches, were conducted. Japanese flounder Paralichthys olivaceus larvae were fed newly designed MD or a combination of them with live food (LF) between 3 and 10 days after hatching (d.a.h.) in experiment I, or between 11 and 20 d.a.h. in experiment II, and compared them to LF and a commercial diet (CD) feeding groups. The growth and survival rates in both experiments were the highest in the LF treatment. But in the microparticle treatment larvae fed MD-Q had a higher survival rate and better growth than those fed MD-T, either alone or in combination with LF. First-feeding larvae fed on MD-Q had a 20.5% survival rate and 1.12 mm gain by 10 d.a.h. Unfed larvae died within 6 d.a.h. These results indicate that using a mixture of different molecular weight peptides is good protein sources and also this type of microparticle diet can be applied to flounder from larval to juvenile stages.     

Changes in lipid content, fatty acid composition and lipid class composition of eggs and developing larvae (0–40 days old) of cultured common dentex (Dentex dentex Linnaeus 1758)

Total lipid content, fatty acid (FA) composition and lipid class composition of common dentex eggs spawned at different times and larvae reared under different culture conditions until 40 days posthatch (dph) were analysed to get a general pattern of lipid composition during larval development. Two groups of larvae were kept under starvation to compare their FA composition with that obtained from normally fed larvae. To compare FA use or accumulation during larval development, results were grouped according to the developmental stage of the larvae instead of age in days posthatch. Saturated and monounsaturated FAs decreased along larval development, while polyunsaturated fatty acid (PUFA) content increased. The ratio of docosahexaenoic acid (DHA)/eicosapentaenoic acid shifted from 4 to 5 in early developmental stages to lower than 1 after metamorphosis. Arachidonic acid levels remained constant along larval development. Larvae kept 6 days under starvation consumed most of their n-3 PUFA while conserving the DHA to values at day 0. The results presented here are useful for the design of nutritional experiments, because there were differences detected in terms of lipid and FA composition between developmental stages with higher differences mainly found in first-feeding larvae and early developmental stages.     

Density and sound speed contrasts of the Japanese common squid Todarodes pacificus and their influence on acoustic target strength

ABSTRACT:   In this study, density and sound speed contrasts were measured for the Japanese common squid Todarodes pacificus . Target strength (TS) data derived from an acoustic scattering model based on measurements of these two parameters were compared with TS values based on acoustic measurement data to determine whether the measured parameters are reasonable values for theoretical scattering model. Density contrast ( g ) was measured from the displacement volume and wet weight, while sound speed contrast ( h ) was measured from the acoustic measurements of travel time (time-of-flight method). The Kirchhoff ray mode model, which represents the squid body as a set of fluid-filled cylinders, was used to calculate theoretical TS. Mean g- and h -values of the squid were 1.029 and 1.041, respectively. Comparison with previous data showed that g was similar, whereas h was relatively high. The difference in the TS between the theoretical model using measured parameters and the acoustic measurement was within 3 dB. Thus, the measured g- and h -values are acceptable for theoretical models of squid.     

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.     

牙鲆仔鱼核酸与生长关系的研究

随机采取不同日龄健康的牙鲆仔鱼,用电子目镜和天平测定其全长（L）、体质量（m）,运用整体匀浆法测定鱼体中核酸和总蛋白浓度、RNA／DNA （a）比值和总蛋白／DNA比值（b）,研究了牙鲆仔鱼的生长,DNA、RNA和总蛋白的变化规律,探讨了核酸、总蛋白和生长的关系。试验结果表明,牙鲆仔鱼体质量、全长与RNA／DNA比值均呈线性负相关,关系式分别为 m＝-19．85 a＋82．79（r2＝0．89, P＜0．01）,L＝-7．41 a＋33．53（r2＝0．85,P＜0．05）。上述关系式说明,牙鲆仔鱼时期的生长以细胞增殖为主,大量消耗前期合成的蛋白质。牙鲆仔鱼体质量、全长与总蛋白／DNA 比值也呈线性负相关,关系式分别为 m＝-0．61 b ＋34．54（r2＝0．93, P ＜0．01）,L＝-0．22 b ＋15．33（r2＝0．86, P ＜0．01）。随着牙鲆仔鱼养殖日龄的增加,总蛋白／DNA比值下降的幅度大于RNA／DNA比值。核酸指标能从细胞水平上分析仔鱼的生长。