东、黄海日本鲭种群鉴定和划分的研究进展

分布于东、黄海的日本鲭(Scomber japoncus)在我国海洋渔业中具有重要的地位,随着中韩、中日渔业协定的生效,开展日本鲭等重要经济鱼类的种群归属研究显得尤为重要。关于东、黄海日本鲭种群划分,20世纪中日两国学者利用标志放流和渔业调查数据分别进行了研判,但中日间以及国内对其种群划分存在不同见解。21世纪以来,中国一些研究者利用形态框架法和分子遗传学方法对前辈的种群划分进行了验证并提供了一些证据,但分析结果值得商榷。总结相关研究结果,多数中国学者将分布于东、黄海的日本鲭划分为东海西部种群、五岛西部种群和闽南—粤东地方种群,也有中国学者将其划分为东海群系和闽南—粤东地方种群;日本学者将分布于东海不同越冬场日本鲭归属为对马暖流群系,也有日本学者将分布于东、黄海和日本海西部的日本鲭划分为九州西部群系和东海西部群系。针对东、黄海日本鲭种群划分存在的不同观点,今后研究者应同时利用目前较为先进的、相对可操作的鱼类框架形态和分子遗传等判别技术,增加产卵场样本采集覆盖面,以获得判别东、黄海日本鲭种群相对最为科学的证据。     

Time course of final oocyte maturation and ovulation in chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> induced by hCG and GnRHa

Abstract:   The question of whether the ovulation and spawning time in chub mackerel Scomber japonicus is entrained by a circadian rhythm was raised by our previous experiments. Further questions were also raised about whether the time course of human chorionic gonadotropin (hCG)-induced final oocyte maturation (FOM) and ovulation reflected the natural time course induced by endogeneous pituitary gonadotropin (GtH). To address these questions, hCG and gonadotropin-releasing hormone analog (GnRHa) were administered at two 'opposite' times, 14:00 and 02:00 hours, and the time courses of FOM and ovulation were compared. When hCG was injected, ovulation occurred 33 h post-injection in both groups, regardless of the timing of the hCG injection. The timing of ovulation in chub mackerel depends on the timing of hCG injection, but apparently not on circadian rhythms. When GnRHa was injected, ovulation began at 36 h post-injection of GnRHa, regardless of the timing of injection. These results indicate that the time course of FOM and ovulation in the chub mackerel followed a similar pattern whether stimulated by hCG injection or spontaneous luteinizing hormone (LH) surge because GnRHa induces the secretion of endogenous GtH (primarily LH) from the fish pituitary. Thus, it is concluded that the time course of hCG-induced FOM and ovulation in chub mackerel follows the natural time course induced by endogenous pituitary LH.     

Influence of death struggle on the structural changes in chub mackerel muscle during chilled storage

ABSTRACT: Chub mackerel (34–35 cm, approximately 500 g), which were caught by fishing with a rod and line at the Bungo Channel, Oita prefecture, were rested overnight in a fish preserve and either killed by decapitation (control group) or allowed to struggle in air for 30 min (struggled group). Muscle samples were excised every 4 h, and measurements on breaking strength and histological observations were done for both groups. The breaking strength of muscle in the control group was significantly higher than that in the struggled group, whereby a decrease in breaking strength was delayed for 12 h compared to the struggled group. Light microscopy showed space extension among muscle cells in association with a decrease in breaking strength. Especially in the struggled group, the extended area was larger and the difference in area was significant at the time when breaking strength showed a significant difference. Using electron microscopy, the extended area showed cut and/or disappeared collagen fibrils. From these results, it was demonstrated that struggling to death promoted the degradation of collagen fibrils and the weakening of connective tissue and, resultantly, led to the faster softening of muscle of chub mackerel.     

Reproductive parameters of the chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> estimated from human chorionic gonadotropin-induced final oocyte maturation and ovulation in captivity

ABSTRACT:   Final oocyte maturation and ovulation of captive chub mackerel Scomber japonicus with fully yolk-accumulated oocytes were induced by a single injection of human chorionic gonadotropin. Reproductive parameters, including spawning frequency and batch fecundity, which are required to estimate spawning biomass in pelagic fish by the daily egg production method, were analyzed. Germinal vesicle migration (GVM) occurred at 18–24 h post-injection, and the hydration and ovulation of oocytes were completed at 30 and 36 h post-injection, respectively. The results of the maturation process suggest that fish with GVM-stage ovaries captured in the daytime from the field are capable of spawning on the night following their capture. The oocytes used in the oocyte size-frequency distribution method for batch fecundity estimates should be at late GVM and more advanced stages. The results of sequential artificial insemination showed that the quality of ovulated eggs held in the ovarian lumen rapidly deteriorated as time progressed after ovulation. This indicates that the fertilization window for the ovulated eggs of chub mackerel lasts only a few hours, and spawning behavior should be performed within a few hours after ovulation in the wild population.     

Effect of Liquid Smoke Dipping and Packaging Method on the Keeping Quality of Raw and Cooked Chub Mackerel (Scomber japonicus) Fillets

Changes in biochemical and sensory attributes of chub mackerel (Scomber japonicus) fillets during storage treated by immersion in a 12% NaCl brine with or without 0.2% liquid smoke were investigated. Brine-treated chub mackerel fillets were packaged in modified atmosphere or under vacuum and were stored at 4°C. The brined fillets were stored and evaluated raw and after heat treatment as cooked samples. Fish fillets were assessed organoleptically to determine acceptability and by measuring the pH, oxidation levels (TBARS test), and total volatile basic nitrogen (TVBN). Fillets treated in brine with liquid smoke exhibited similar pH and significantly lower TBARS and TVBN values (p < 0.05). The combination of the use of brines containing liquid smoke and subsequent vacuum packaging produced the lowest TBARS and TVBN values and resulted in extended acceptability.     

Age validation,growth and annual reproductive cycle of chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> off the waters of northern Kyushu and in the East China Sea

The age and growth of chub mackerel Scomber japonicus collected from the East China Sea and the northern waters off Kyushu between June 2000 and June 2001 were determined by observing the otolith surface after dipping it in xylene. The translucent and opaque zones on the otolith surface were identified, and the number of translucent zones was counted. Monthly changes in the frequency of fish with translucent zones on the otolith margin, and in the marginal increments, indicated that the translucent zones were formed between April and June. The seasonal pattern of annulus formation on the otolith became clear by observing the otoliths of fish with known ages, and the otolith formation in wild fish was consistent with that of fish with known ages. The mean gonadosomatic index of male and female fish was high from March to May, and spawning females were observed from mid-March to mid-May. The estimated ages were 1–5 years for males and 1–6 years for females. The von Bertalanffy growth parameters did not significantly differ between male and female. The model was obtained as FL _t=406×{1−exp[−0.372×(t+1.68)]     

东海南部鲐鱼生物学特性的初步研究

本文对东海南部的鲐鲹鱼类的叉长、体重及性腺成熟度等进行了初步分析,认为1999年5月份东海南部鲐鱼优势叉长组为26～28cm,优势体重组为200～300g;7、8月份优势叉长组为24～26cm,优势体重组为100～200g。蓝圆鲹优势叉长组为20～21cm。2000年7、8月份鲐鱼优势叉长组为24～26cm。1999年鲐鱼叉长组成基本呈正态分布,2000年鲐鱼叉长组成明显存在两个峰值。2000年相同叉长的鲐鱼体重要略低于1999年,认为跟1999年、2000年海洋环境因子变化有关。从相关系数来看,2000年的曲线更贴近实际情况。并认为5月份北上参加产卵洄游的鲐鱼群体、其性腺已开始发育成熟,并沿途产卵。     

Temperature conditions in the Argentine chub mackerel (Scomber japonicus) fishing ground: implications for fishery management

We describe the seasonal migrations of Argentine chub mackerel ( Scomber japonicus ) into the fishing ground in relation to sea surface temperature conditions and analyse the temperature evolution during the fishing season on the basis of 1955–97 time-series. The upper temperature limit for the presence of schools was around 19°C. At higher values, most schools leave coastal waters (< 50 m) for the shelf. An inverse relationship was observed between catches per unit of effort (CPUE) of the inshore fishery and sea surface temperature. The highest standardized CPUE values corresponded to temperatures lower than 19°C. Above this temperature, the probability of obtaining a standardized CPUE higher than 1 was extremely low, and the standard deviations were minimal. The economic benefit from catches was also analysed through the different months of the fishing season. It was found that the mean benefit corresponding to temperatures lower than 19°C exceeded approximately 15 times that obtained at higher temperatures. A simple fishing strategy was proposed to the commercial fleet in order to improve the economic benefit of the catches. The migratory pattern followed by mackerel during the spawning period was also analysed in relationship to other environmental factors like food availability. Zooplankton composition, size structure and abundance in coastal and shelf waters are described, and their implications for feeding ecology of larvae and adults of the species are discussed.     

Morphology, endocrinology, and environmental modulation of gonadal sex differentiation in teleost fishes

Successful reproduction by an adult depends on the normal ontogenesis of the gonads, a complex process of cellular and histological differentiation that starts early in life. This process is theoretically predetermined by genetic factors and includes sensitisation of the bipotential gonads to endogenous endocrine factors prior to, during and even after commitment to maleness or femaleness. However, young fish are relatively vulnerable to a host of environmental (physical and chemical) factors that can affect this endogenous endocrine axis, disturbing or even overriding the putative developmental pathway. This sexually lability can be exploited to our advantage for the production of monosex fish populations of the most valuable sex for food production or aquarium fish trade. On the other hand, it represents also a potential path for undesirable influences from endocrine-disrupting chemicals and climatic factors, particularly environmental temperature. This paper provides a detailed account of the early histological process of gonadal sex differentiation, with special reference to gonochoristic species, and reviews the criteria employed to positively identify ovarian and testicular differentiation. It also reviews the development of endocrine competence and sensitivity of the differentiating gonads to exogenous influences in the context of the relative stability of genotypic sex determination in various fish species. Sex differentiation in some species seems to be under strong genetic control and may not require endogenous sex steroid production. Conversely, reliance on endogenous sex steroids for gonadal differentiation is observed in other species and this phenomenon is apparently associated with a higher incidence of environment (mainly temperature)-labile sex differentiation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Growth of juvenile chub mackerel Scomber japonicus in the western North Pacific Ocean: with application and validation of otolith daily increment formation

The growth of juvenile chub mackerel Scomber japonicus collected in the western North Pacific Ocean in 2007 and 2009 was examined based on the evidence of otolith daily increment formation in captive specimens. There was a significant difference in the relationship between known age and number of increments in the frontal and sagittal planes. Repeated markings on the otolith using Alizarin complexone and the coefficient of variation in number of increments suggest that the increments in the frontal plane of the otolith are more suitable for age estimation than those in the long and short axes of the sagittal plane. The increments in the frontal plane formed daily, and the first ring was usually deposited 3 days after hatch. Age of wild juveniles ranged from 24 to 211 days after hatch based on the frontal plane method. The estimated hatching periods of specimens ranged from February to June, but the April-hatched specimens were collected throughout the sampling periods of 2007 and 2009. The Gompertz growth model showed a difference in growth pattern in specimens between 2007 and 2009. The juveniles in 2009 appeared to grow more quickly than those in 2007 until summer, but thereafter the 2009 specimens seemed to grow more slowly.     

Occurrence of postmortem myoliquefactive kudoosis in Atlantic mackerel, Scomber scombrus L., from the North Sea

Members of the myxosporean genus Kudoa occur in various marine teleosts worldwide. Several species are of concern to the fishery and aquaculture industries as they may produce unsightly cysts in the fish host's musculature or are associated with postmortem myoliquefaction of the fish muscle, commonly referred to as 'soft flesh'. This study describes the occurrence and effects on a host of a Kudoa species in Atlantic mackerel, Scomber scombrus , from the northern North Sea. Generalized postmortem myoliquefaction associated with Kudoa sp. occurred in 0.8% of the examined fish, i.e. 11 of 1339 mackerel developed 'soft flesh'. There was a significant difference in the prevalence of myoliquefaction between medium sized (400–600 g) and large mackerel (>600 g). The prevalence reached 8.9% in the latter host size group. No subclinical infections of Kudoa sp. were detected when examining fresh muscle ( n  = 103) and blood ( n  = 165) samples for spores using light microscopy. Affected mackerel developed generalized myoliquefaction after 38–56 h post-catch. No inflammatory host response was associated with the presence of plasmodia within single body muscle fibres of 'soft flesh' affected fish. Based on comparison of myxospore dimensions and analysis of the nuclear small subunit (SSU) ribosomal DNA, the present Kudoa species is assigned to Kudoa thyrsites . However, due to the species' apparently very wide geographical distribution and host range, its varying effect on different fish host species, together with the still unknown life cycle of Kudoa spp., the taxonomic status of K. thyrsites appears not to be fully resolved.     

产卵深度变动对东海日本鲭鱼卵仔幼鱼输运和存活率的影响

日本鲭(Scomber japonicus)是我国近海重要经济鱼种,海洋环境变动对鱼类生命周期中最为脆弱的鱼卵和仔幼鱼的生长、存活直至种群补充产生重大的影响,其中产卵深度变动对其是否会产生影响,目前尚不清楚。为此,本文拟采用FVCOM(Finite-Volume Coastal Ocean Model)物理模型来模拟三维物理场,使用基于个体模型IBM(individual-based model)参数化并模拟日本鲭的早期生活史,从而建立起基于物理-生物个体的东海日本鲭初期生态耦合模型,使用该耦合模型模拟了日本鲭产卵水深不同导致鱼卵仔幼鱼从产卵场向育肥场的输运过程中经历物理环境的差异对鱼卵仔幼鱼的输运分布以及存活率的影响。研究发现,产卵深度的变动,未对鱼卵仔幼鱼的输运分布产生明显影响,但在输运过程中所处水深和水温的微小差异却导致了变浅(5 m)和加深(15 m)产卵深度鱼卵仔幼鱼的存活率降低,正常产卵深度(10 m)是最佳的产卵水深。因此,研究认为产卵深度的细微变动将会对东海日本鲭鱼卵仔幼鱼的存活率产生影响,但对鱼卵仔幼鱼输运则影响不大。     

Environmental factors and recruitment of mackerel, Scomber scombrus L. 1758, along the north-east Atlantic coasts of Europe

Increasingly, scientific publications refer to some of the environmental factors affecting the recruitment in fish species. However, presently, there is little information available concerning the influence of the environment on the recruitment of Scomber scombrus, the North-east Atlantic mackerel (NEAM). In this contribution, North Atlantic Oscillation (NAO), upwelling and turbulent mixing (or `turbulence') series were compared with recruitment estimates, at age-0. The results show that the southern prespawning migration pattern of the Atlantic mackerel is directed towards areas with low turbulent mixing at spawning time, providing a `stable environment' for egg and larval survival. In the southern areas, where the spawning starts, the turbulence conditions of prespawning and spawning periods have the largest influence on the success of recruitment; this is related, possibly, to the more `stable' weather in the subsequent months and for the remainder of the year. In contrast, in the northern areas, the role of turbulence over the entire year becomes increasingly more relevant; this is related, possibly, to the high levels of turbulence during autumn and winter, which may become limiting to the survival of juveniles. About 50% of the variability in the Atlantic mackerel recruitment may be explained by means of environmental variables, such as turbulence. Other variables, such as upwelling and NAO, are only slightly, or not, statistically significant.     

Spawning frequency of the Tsushima Current subpopulation of chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> off Kyushu,Japan

Female Japanese chub mackerel Scomber japonicus of the Tsushima Current subpopulation were collected during the spawning season from March to May 2001. A total of 137 adult females were caught between midnight and daybreak. A considerable number of fish displayed new postovulatory follicles (POF), whereas there was no evidence of germinal vesicle breakdown or hydrated oocytes in any of the fish collected. This suggests a daily spawning synchronicity toward midnight. To estimate the spawning frequency (S), the female reproductive state was classified into four criteria based on the degenerative stage of the POFs and the developmental stage of the oocytes. To stage the POFs according to age and determine the stage duration, ovaries from S. japonicus were induced to spawn in the laboratory and were sampled 0–72 h after ovulation at appropriate intervals. The average S, which is evaluated from four different indices, was 16.9%, corresponding to the average female chub mackerel spawned every 5.9 days (8.5 times) during the 50 days.     

Molecular mechanisms of sex determination and gonadal sex differentiation in fish

We have used various genetic and molecular approaches to investigate the mechanisms of sex determination and gonadal sex differentiation in fish. DMY was identified as the sex-determining gene of medaka. In tilapia, endogenous estrogens act as natural inducers of ovarian differentiation, while DMRT1 may be important for testicular differentiation. The roles of these regulators in sex determination and gonadal sex differentiation were ascertained using a gene or hormonal blockade strategy.     

Gonadal sex differentiation and sex control in red sea bream, Pagrus major

The gonadal sex differentiation in red sea bream, Pagrus major, which is one of the most important species for aquaculture in Japan, was revealed histologically. The suitable conditions for induction of all-male groups in the fish were investigated, and functional males were induced by the conditions of oral administration of 17α-methyltestosterone. The sex determination of this fish was also discussed.