Gonadal maturation and spawning migration of stocked female barfin flounder Verasper moseri off the Pacific coast of northern Japan

Commercial catches of barfin flounder Verasper moseri, an important target flatfish for stock enhancement programs in northern Japan, have recovered remarkably since the large-scale release of seedlings from Hokkaido in 2006. However, their reproductive ecology remains unclear. Our study of 2008–2012 investigated seasonal changes in the maturity of stocked female barfin flounder (n = 4,123) off the Pacific coast from Hokkaido to Tohoku (35.7°–43.4°N). Histological observation of ovaries revealed that fish undergoing vitellogenesis were observed mainly off Hokkaido and partially off northern Tohoku during August–January (40.2°–43.4°N). However, fully matured or spawning fish were not found near those areas. They were observed only in southern Tohoku. Ongoing spawning was observed off southernmost Tohoku (35.8°–37.5°N around 300 m depth) from early February through late April, when commercial landings had decreased drastically off Hokkaido. Spent fish were caught only rarely off southern Tohoku, but were observed frequently off Hokkaido during April–June. These results demonstrate that spawning grounds form at the upper continental slope off southernmost Tohoku during February–April. Relations between maturation traits and seasonal landings strongly suggest that female barfin flounder repeatedly migrate more than 700 km from feeding grounds off Hokkaido to spawning grounds off southern Tohoku.     

条斑星鲽卵巢发育规律和性类固醇激素周年变化研究

采用组织学方法、形态测量法、放射免疫法(RIA)等技术方法,研究了人工养殖条件下条斑星鲽雌性亲鱼卵巢发育成熟和性类固醇激素的年周期变化规律.结果表明,条斑星鲽属于非同步分批产卵类型.卵母细胞按其组织学特点可分为6个时相,卵巢发育依据其形态特征可划分为相应的6个时期.卵巢年周期发育过程中,性腺指数(GSI)、肝脏指数(HSI)和肥满度(CF)发生变化,表现出与性腺发育协同一致的变化规律.统计分析表明,卵巢年周期发育过程中,GSI和HSI值与CF值都存在显著的正相关关系,GSI值的变化与水温调控呈显著的负相关关系.亲鱼血浆中雌二醇(E2)在6月份开始升高,9月份达到年周期中的第1个小高峰,翌年2月份,E2表达水平达到最高峰值,4月产卵结束后,E2表达水平降低并维持较低水平至下一个生殖季节.血浆中睾酮(T)含量在7月达到第1个峰值,并在翌年1月份达到第2个峰值,在4月份产卵后降至最低水平并维持至下一个生殖季节.统计分析表明,E2与T存在正相关关系,E2与光周期调控存在正相关关系,同时与GSI和CF呈弱的正相关关系.     

Genetic evaluation of interindividual relatedness for broodstock management of the rare species barfin flounder Verasper moseri using microsatellite DNA markers

ABSTRACT:   The barfin flounder has been recently declared to be rare, as the number of wild individuals in Japan has greatly reduced since 1975. The Japanese National Center for Stock Enhancement started the stocking program for this species on 1987. In the present study, microsatellite DNA loci were applied in order to determine the pedigree of the hatchery-produced juveniles for stock enhancement. Additionally, using six polymorphic microsatellite markers, the accuracy to assign dyads to categories of kinship was estimated using the relatedness estimator ( R _XY), similarity indexes (individual genetic identity [GI] and proportion of shared alleles [ P _S]), identification of kin groups using unweighted pair group method with arithmetic mean (UPGMA) clustering based on interindividual genetic distances (1- R _XY, 1- P _S, and 1-GI), a likelihood ratio approach, and partition methods to separate individuals into cohorts. The results were compared with the pedigree relationship previously obtained from parentage analysis. Estimation of the kinship relationship between individuals could be better inferred by means of UPGMA dendrogram clustering based on 1-GI or 1- P _S as interindividual genetic distances, or using computer software to perform partitioning of set of individuals.     

Molecular cloning, characterization expression of P450c17-I and P450c17-II and their functions analysis during the reproductive cycle in males of barfin flounder (Verasper moseri)

P450c17, a key steroidogenic enzyme, plays important roles in the production of sex steroid and cortisol. In teleost, there are two types of P450c17, P450c17-I possessing 17α-hydroxylase and 17, 20-lyase activities, and P450c17-II only possessing 17α-hydroxylase activity. This work describes the molecular cloning of the cDNA encoding the barfin flounder (Verasper moseri) P450c17-I and P450c17-II by means of RT-PCR and 5' and 3' rapid amplification of cDNA ends (RACE) analyses and mRNA expression profiles analyzing by semiquantitative RT-PCR. Respectively, P450c17-I and P450c17-II mRNA levels in the testes correlated with serum testosterone (T) level, as well as gonadosomatic index (GSI) of males during specific stages of spermatogenesis. P450c17-I and P450c17-II mRNA were expressed in the testis and ovary, suggesting that both of them participate in the production of sex steroid in barfin flounder gonads. P450c17-I mRNA was undetectable; in contrast, P450c17-II mRNA was detected at the highest level in the head kidney, meaning that only P450c17-II is involved in the production of cortisol in barfin flounder. The results demonstrated that both of P450c17-I and P450c17-II participate in the production of sex steroid in male barfin flounder gonads.     

Monitoring of the genetic variability of the hatchery and recaptured fish in the stock enhancement program of the rare species barfin flounder <Emphasis Type="Italic">Verasper moseri</Emphasis>

ABSTRACT:   In relation to the stock enhancement program for barfin flounder, hatchery juveniles produced in 2001 were genotyped using microsatellite DNA markers (msDNA) and then released to natural waters. Subsequently, recaptured individuals, designated as 'tentative recaptured', were examined using msDNA. In order to evaluate the effectiveness of the stock enhancement program, pairwise F _ST and genic differentiation tests were used to estimate the genetic divergence between the wild samples, the hatchery broodstock, and the tentative recaptured samples. Analysis showed significant differentiation among these three groups. Pedigree determination by msDNA was used to establish the origin of the tentative recaptured individuals, in order to elucidate whether they were hatchery produced, 'real recaptured', or wild specimens. Wild individuals were not found. The effective population size of the real recaptured stock was very low ( N _e = 16.6). Equal family survivability was observed between the released and real recaptured stocks, indicating that the genetic variability of the released stock was maintained in the natural environment. Future broodstock management, breeding designs, and family contribution equalization of the offspring to be released will be required in this rare species to avoid unintended genetic differentiation between the wild population and the hatchery broodstock.     

Pedigree analysis of recaptured fish in the stock enhancement program of spotted halibut Verasper variegatus

ABSTRACT:   Spotted halibut Verasper variegatus hatchery juveniles produced in 2002 were genotyped using three microsatellite DNA markers (msDNA) and then released into natural waters. Subsequently, recaptured individuals were examined using msDNA. In order to evaluate the effectiveness of the stock enhancement program, from the genetic point of view, a pairwise F _ST test was implemented to estimate the genetic divergence between the wild captive broodstock, the hatchery offspring and the recaptured samples. The analysis showed significant differentiation between the broodstock and recaptured samples. Pedigree determination using msDNA was used to calculate the effective population size of the recaptured stock, which was found to be very low ( N _e ≈ 8). Equal family survivability was observed between the two recaptured stocks, but not between the released and recaptured stock. The number of identified families was higher and more equalized in the hatchery offspring compared to the recaptured samples, where the number of families declined. This fact was caused by an unequal family survivability just before or just after release. Separately, the number of contributing parents to the hatchery offspring was lower than the broodstock census number. Consequently, these two facts caused the genetic divergence of the recaptured stock from the broodstock.     

Genetic diversity of red sea bream Pagrus major in western Japan in relation to stock enhancement

SUMMARY: Stock enhancement is used in Japan as a tool to help the replenishment of wild populations of red sea bream Pagrus major . In this study, we analyzed the genetic diversity and composition of wild red sea bream at seven locations around Shikoku Island, South-west Japan, using three microsatellite loci. This analysis was done to test the hypothesis that: (i) red sea bream comprises a single Mendelian population along Japan; and (ii) stock enhancement programs around Shikoku Island are causing genetic differentiation among wild stocks. The results indicated that some locations from the Shikoku area were not significantly different from the rest of Japan, supporting the hypothesis of a single Mendelian population. Significant departures from Hardy–Weinberg equilibrium and significant pairwise F_ST among locations indicated genetic instability within this region. We suggest that the stock enhancement programs made in the region are the possible cause of this genetic instability. A management scheme for the hatcheries involved in the stock enhancement of red sea bream is presented.     

Occurrence of Pacific bluefin tuna Thunnus orientalis larvae off the Pacific coast of Tohoku area,northeastern Japan: Possibility of the discovery of the third spawning ground

Recently, based on the histological studies it is suggested that Pacific bluefin tuna (PBF) spawns in the Kuroshio–Oyashio transition, off the Pacific coast of northeastern Japan, in addition to the previously identified two spawning areas of the northwestern Pacific around the Nansei Islands and the Sea of Japan. Distributional surveys for PBF larvae have not been conducted in the Kuroshio–Oyashio transition, and thus, we conducted PBF larval surveys at twenty stations in this area in early August 2018 to obtain evidence for the spawning of PBF. Twelve PBF larvae (3.9–7.2 mm in body length) were collected at six stations where sea surface temperature ranged from 27.2 to 28.2°C. Otolith microstructure analysis indicated that age of these larvae ranged from 4 to 11 days after hatching and the larvae hatched in late July. Growth of the collected larvae was comparable to those in the other two spawning grounds. Therefore, PBF spawns, hatches, and at least survives to the postflexion stage, 11 days after hatching in the Kuroshio–Oyashio transition. This fact potentially has a large impact on recruitment processes of PBF if they survive to recruitment in this third spawning ground.     

Weight-based virtual population analysis of Pacific cod Gadus macrocephalus off the Pacific coast of southern Hokkaido, Japan

ABSTRACT:   Age-based population assessment is widely used, but there are cases where information on age or even body length of landed fish is difficult to collect. In the present study, the biomass and fishing mortality of the southern Hokkaido stock of Pacific cod Gadus macrocephalus was estimated directly from body weight composition, using weight-based virtual population analysis, from 1994 to 2000. The estimated biomass over 1 kg body weight was 5607 t in 1994 and increased to 7908 t in 2000. The increase was explained by an increase in recruitment.     

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.     

渤海渔业生物生殖群体结构及其分布特征

根据2004年春季渤海底拖网调查资料,从渔获物的种类组成、渔业资源结构、优势种以及重要鱼类的体长、体重和性腺成熟度等方面分析了渤海渔业生物生殖群体结构,并利用聚类分析法对生殖群体的区域集群进行了研究.结果表明,春季渤海的生殖群体种类仅为51种,资源量指数为1.54kg/网·h,与20世纪80、90年代相比,优势种更替明显,生殖群体结构的小型化、低龄化更加突出;生殖群体区域集群分布明显,渤海中部和渤海湾的种类组成最相近,相似指数达到67.67%.     

Interannual changes in the timing of walleye pollock spawning migration and their impacts on the gillnet fishery in the southwestern Pacific coast of Hokkaido,Donan area,Japan

The southwestern Pacific coast of Hokkaido is the main spawning ground for the Japanese Pacific stock of walleye pollock Theragra chalcogramma. A commercial gillnet fishery targeting spawning adult pollock in this area mainly operates from October to January to coincide with the migration of adult pollock from the feeding ground. Given the results of acoustic surveys, and changes in the proportion of the monthly total catch that was monthly walleye pollock caught by the commercial gillnet fishery, it is thought that the timing of walleye pollock spawning migration to the Donan area varies among years and that the pollock catch of the gillnet fishery clearly reflects changes in pollock abundance in this area. A time series of interannual variability in catch data from 1980 to 2005 suggested that adult pollock migrated and concentrated on their spawning ground later in the 1980s and after 2000 than in the 1990s. Such decadal-scale shifts are presumably caused by climatic changes (e.g., in water temperature) in the Oyashio region. These shifts affect the gillnet fishery through differences in monthly unit prices of pollock and changes in the formation of fishing grounds. These scientific findings can aid the establishment of rules for more efficient walleye pollock resource management under the total allowable catch system.     

春季钓鱼岛海域竹鱼产卵群体生物学特征的研究

利用2005年3月在钓鱼岛海域捕获的竹鱼产卵群体样品测定数据,对其主要生物学特征、主要产卵期和繁殖力特征进行了研究。结果表明,钓鱼岛海域是春季东海南部竹鱼的主要产卵场,主要产卵期为3月中下旬。根据叉长和体重的频率分布图,可以看出该产卵群体主要有3个叉长优势组,其中以200～220mm和230～240mm叉长组为主,260～270mm叉长组个体极少;体重的组成特征与叉长组成基本一致。由于所取样品处于产卵后期,因此条件生长因子相对较小。个体绝对生殖力在12264～37629粒/尾,个体平均绝对生殖力为27844±10179粒/尾;单位长度生殖力范围为50～157粒/mm,平均值为121±42粒/mm;单位纯体重生殖力为82～238粒/g,平均值为202±68粒/g。     

Occurrence and distribution of settling and newly settled spotted halibut Verasper variegatus and Japanese flounder Paralichthys olivaceus in shallow nursery grounds around Shimabara Peninsula, western Japan

The occurrence and distribution of settling and settled spotted halibut Verasper variegatus were compared with those of Japanese flounder Paralichthys olivaceus in shallow habitats around Shimabara Peninsula, western Japan, to elucidate the settlement and recruitment characteristics of spotted halibut, a rare pleuronectid flatfish in Japan. Push-net sampling conducted at nine sites in March and April 2003 collected spotted halibut from four nurseries located at eastern areas of Shimabara Peninsula in Ariake Bay; Japanese flounder were sampled from eight nurseries. Comparison of microhabitat distributions in a tidal-flat nursery during February?CApril in 2003?C2007 revealed that metamorphosing larvae and juveniles of spotted halibut, which showed the drastic body coloration (black to brown) and behavioral changes (frequent swimming to settlement), were distributed mainly in the lower edge of the intertidal area, whereas Japanese flounder inhabited both intertidal and subtidal areas. Metamorphosing larvae of spotted halibut (12.6?C16.5?mm standard length; n?=?24) were collected in March when the highest densities were observed, whereas metamorphosing larvae of Japanese flounder (10.0?C15.9?mm, n?=?55) were observed during March?CApril. Our results suggest that spotted halibut has a narrower time/space window for recruitment to the specific nurseries compared with Japanese flounder.     

中国鲷科鱼类分类和系统发育研究进展

为研究黑鲷(Sparus inacrocephalus)增殖放流最适宜运输密度及运输后生理生化变化情况,选取全长9~11.7 cm的黑鲷鱼苗为实验对象,设计5个密度组(10尾、15尾、20尾、25尾和30尾)采用塑料袋密封充氧运输方式,即塑料袋中充等量的海水并充氧至饱和,水体为育苗池海水,水温27.7 ℃,盐度29,pH 8.04,溶解氧8.8 mg·L^–1,运输2.75 h。分别于运输后暂养的第0、第6、第12、第24和第48小时取样,研究黑鲷鱼苗血清和肌肉中总蛋白(TP)、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、丙二醛(MDA)等指标的变化情况。结果显示,不同密度的塑料袋密封充氧运输后,10尾组和15尾组血清和肌肉中的TP和MDA浓度低于30尾组(P<0.05),而SOD和CAT活性显著高于30尾组(P<0.05);从暂养后恢复水平上看,10尾组和15尾组肌肉和血清中各项指标恢复最快,20尾组和25尾组次之,30尾组的各项指标恢复较慢且至实验结束时未能全部恢复。综合经济因素分析,在水温27.7 ℃、盐度29、pH 8.04的条件下运输9~11.7 cm黑鲷鱼苗2.75 h时,用塑料袋密封充氧运输的最佳密度为每袋25尾。     

Growth of the brittle star Ophiura sarsii sarsii in Funka Bay,Hokkaido, Japan

Fisheries Science - The brittle star Ophiura sarsii with a disc diameter (DD) of less than 9&nbsp;mm is an important prey item for flathead flounder Hippoglossoides dubius in Funka...