Two spawning stocks of icefish <Emphasis Type="Italic">Neosalanx taihuensis</Emphasis> revealed from annual reproductive cycle analyses

Neosalanx taihuensis were sampled from the Tian-e-zhou Oxbow from March 2006 through November 2007. Two separate spawning seasons were identified based on the annual reproductive cycles of the females, designated as the autumn-spawning season and the spring-spawning season. Lifespan of the offspring of the spring-spawning fish was 1 year, with them dying after the subsequent spring spawning. Autumn-spawned females seem to be the offspring of the spring-spawning fish, based on monthly changes in the length–frequency distributions. Spring-mature females had higher absolute fecundity, gonadosomatic index, and relative condition factor in 2007 than in 2006. Relative condition factor of the immature female offspring of spring-spawning fish was higher in 2007 than in 2006, portending a further increase in reproductive investment during the spring spawning of 2008. The increasing reproductive investment suggests that the population of N. taihuensis in the Tian-e-zhou Oxbow may be recovering from its recent decline.     

Elemental fingerprinting in otoliths reveals natal homing of anadromous Baltic Sea pike (Esox lucius L.)

We examined the element pattern in the otoliths of a migratory fish species that inhabit the coastal areas in the brackish of the Baltic Sea. The northern pike (Esox lucius) show migratory behaviour, spawning in streams and rivers and foraging in the sea. We examined spawning migration in four nearby streams in the south‐west part of the Baltic. Otolith analysis by microPIXE revealed unique elemental patterns (Sr, Zn, Br, Co and Mn) for the juveniles in each of the different streams. The strontium signal in the otolith of the juveniles was used as an indicator of freshwater origin and the time spent in the stream. Adult pike in their migrating spawning phase were caught in each of the streams. The elemental composition in otoliths in their freshwater phase (using juvenile pike in the streams as references) was determined. A principal component analysis showed that the elemental fingerprint during the freshwater phase several years back in time was similar for the adult fish and for juveniles inhabiting the stream today. The results indicated natal homing of the adults to a specific stream, a conclusion that was strengthened by the fact that marked fish returned to spawn over consecutive years. Anadromous pike in the Baltic Sea may thus be divided in subpopulations. The results of the study may have implications for fishery management, as pike in the Baltic Sea cannot be seen as homogenous population.     

Otolith microstructure of chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis>: formation of sea entry check and daily deposition of otolith increments in seawater conditions

To apply otolith microstructure to examination of age and growth of juvenile chum salmon Oncorhynchus keta inhabiting coastal waters, formation of otolith increments was investigated for juveniles reared in a seawater aquarium and in net pens. In all otoliths examined, a distinctive check was formed at the time of sea entry of the fish. The deposition of otolith increments after the check was daily for rearing both in the aquarium (57 days) and in the net pens (26 days). Check formation associated with sea entry was also observed in otoliths of juvenile salmon collected 1 km off the coast of Shari, Hokkaido, Japan. Transmitted light observation of otoliths of those fish revealed a transition in otolith increment appearance from dark to light. Otolith Sr: Ca ratio remarkably changed from a low to a high level, coinciding with the transition in otolith appearance. It is suggested that the transition was associated with individual sea entry. This study demonstrated that the check and/or transition associated with sea entry are applicable to a benchmark for otolith increment counts of juvenile chum salmon inhabiting coastal waters.     

Interannual differences in growth and hatch‐date distributions of early juvenile European anchovy in the Bay of Biscay: implications for recruitment

In order to understand better the recruitment variability in European anchovy in the Bay of Biscay, it is important to investigate the processes that affect survival during the early life stages. Anchovy juvenile growth trajectories and hatch‐date distributions were inferred over a 3‐year period based on otolith microstructure analysis. Otolith growth trajectories showed a characteristic shape depending on their hatch‐date timing. Earlier‐born juveniles had notably broader maximum increments than later born conspecifics, resulting in higher growth rates. This observation suggests that early hatching would be beneficial for larval and juvenile growth, and, therefore, survival. The estimated juvenile hatch‐date distributions were relatively narrow compared with the extended anchovy spawning season (March–August) in the Bay of Biscay and indicated that only individuals originated mainly from the summer months (June–August) survived until autumn. Hatch‐date distributions were markedly different among years and seemed to influence the interannual recruitment strength of anchovy. We conclude that years characterized by juvenile survivors originating from the peak spawning period (May and June) would lead to considerable recruitment success. Downwelling events during the peak spawning period seem to affect larval survival. Furthermore, size‐dependent overwinter mortality would be an additional process that regulates recruitment strength in the anchovy population in the Bay of Biscay.     

苏北浅滩沙脊潮沟地形对鱼类分布格局的影响

为研究苏北浅滩沙脊潮沟海域地形特征对鱼类群落分布格局的影响,根据2011年5月(春)和2010年11月(秋)在苏北浅滩中部海域渔业资源调查的资料,采用方差贡献和回归分析的方法,通过对中部海域沙脊潮沟处鱼类生物学特征、资源密度、优势种相对重要性指数以及优势种对鱼类总数量的贡献的分析,讨论苏北浅滩沙脊潮沟地形对鱼类分布格局的影响。结果显示,鱼类空间分布差异与潮沟系统的地形地貌有关,春季潮沟外侧海域是小黄鱼、鰐等洄游性鱼类的渔场,潮沟海域是洄游性鰐和方氏锦鰑的渔场位置,沙脊海域是赤鼻棱鰒等非洄游性鱼的渔场。秋季鱼类空间分布仅与潮沟系统沙脊地形相关,沙脊海域主要是大银鱼的索饵场和越冬场。鱼类数量季节变化还与鱼类产卵洄游和生长相关。春季重量密度(16.08 kg/km2)大于秋季(10.74 kg/km2),而秋季尾数密度(16.3×103尾/km2)大于春季(5.36×103尾/km2)。春季鱼类规格较大,与部分成鱼具有到这一海域进行产卵洄游的习性有关,而秋季同种鱼则以幼体居多,且优势种个体小,与秋季部分鱼类幼鱼在此处索饵和育幼有关。总体上,苏北浅滩沙脊潮沟海域特有地形,使得这一海域春季是鱼类的产卵场,夏秋季是育幼场,因而在渔业上具有重要的意义。     

福建诏安湾春、秋季鱼卵和仔稚鱼种类组成及数量变化

2012年10月和2014年5月在诏安湾海域进行了鱼卵、仔稚鱼的调查,对诏安湾秋季和春季的鱼卵和仔稚鱼的种类组成、数量和分布进行了研究。结果表明,本调查海域共鉴定的鱼卵7种、仔稚鱼7种,隶属于10科10属;秋季共采集到鱼卵31个和仔稚鱼47尾,密集区出现在湾口的西屿北侧海域,春季共采集到鱼卵662个和仔稚鱼69尾,密集区主要分布在诏安湾中部偏北海域和湾口西屿西侧海域。秋季主要优势种为隆头鱼科鱼类、美肩鳃鳚,春季主要优势种为黄姑鱼、红鳍笛鲷和美肩鳃鳚。与东山湾相比,春季诏安湾鱼卵密度明显较大、仔稚鱼资源密度略低;秋季两个海湾的鱼卵、仔稚鱼数量均处于低水平;两个海湾的产卵时期主要在春季。     

虹鳟、金鳟亲鱼成熟群体卵质比较研究

对相同饲养条件下经产虹鳟和初产金鳟亲鱼自然成熟产卵群体生物学特性及其成熟鱼卵中四种不饱和脂肪酸（亚油酸,亚麻酸,EPA,HDA）组成含量进行分析比较,结果表明：两种鱼成熟产卵期和成熟卵粒重相近;成熟鱼卵四种脂肪酸组成含量（mg/g鲜样）均依次为亚油酸＞DHA＞EPA＞亚麻酸,相关明显（R=0.97),虹鳟鱼卵四种脂肪酸总和（6．68）,必需脂肪酸（3．83）,DHA（2．534）含量明显高于金鳟（3．93,2．21,1．14）。金鳟受精卵发眼率较低,可能与鱼卵EFA,DHA含量低有关。     

Seasonal changes in otolith increment width trajectories and the effect of temperature on the daily growth rate of young sardines

We studied the otolith microstructure and growth of sardine, Sardina pilchardus, in the North Aegean Sea (eastern Mediterranean Sea), using samples of larvae and juveniles that had hatched in winter (November–January) and winter–spring (February–May), respectively. The juveniles had developed during an extended period coinciding with marked pelagic ecosystem changes (from winter, mixed conditions to summer, stratified waters). To examine the relationship between environmental changes and the observed variability in their otolith increment–width trajectories (width‐at‐age), we summarized the shape of trajectories with a four‐parameter set estimated from a growth model fit to each width trajectory. The individual parameter sets were then related to the potential oceanographic conditions that fish experienced during their development, derived from a hydrodynamic–biogeochemical model (POM‐ERSEM), implemented in the sampling area. Substantial seasonal effects were demonstrated on the otolith microstructure (platykurtic versus leptokurtic trajectories in winter‐mixed versus summer‐stratified conditions), which were related to the progressive sea surface warming. In a subsequent step, in order to study the effect of oceanographic conditions on larval and juvenile daily growth rates, a GAM (Generalized Additive Model) analysis of otolith increment widths was carried out, using model‐derived oceanographic parameters and taking into account the ‘inherent otolith growth’, expressed by the explanatory variables ‘previous increment width’ and ‘Age’. Results showed a strong and positive, linear effect of temperature on the growth rate of winter‐caught larvae, whereas in juveniles, which had developed within a wide range of temperatures, an optimum temperature for growth was observed at around 24°C.     

Daily and sub-daily otolith increments of larval and juvenile walleye pollock, Theragra chalcogramma (Pallas), as validated by alizarin complexone experiments

Walleye pollock (Theragra chalcogramma) were reared from eggs to the juvenile life stage to study daily increment formation in the sagittae otoliths, which are routinely used for age and growth analyses. The apparent deposition of sub-daily growth increments becomes problematic for determining fish age from the late larval stage throughout the juvenile (young-of-the-year) development stage. Otolith marking experiments were conducted to determine interpretation criteria to differentiate between daily and sub-daily increments. Immersion of larval and transforming walleye pollock in 25 mg/l of alizarin complexone (ALC) for 6 h once a week produced a fluorescent mark on the day of staining. Evidence of six well defined and equally spaced increments counted between the weekly ALC marks validated the deposition of daily increments. The daily increments gradually increased in width as the fish/otolith grew. The criteria for determining the presence of sub-daily increments between the daily increments were (1) weak optical definition and (2) a sudden change in incremental distance that lasted for one or two increments and were approximately <0.5 μm in width. Growth problems that occurred during the experiments were identified on otoliths as reductions in daily incremental widths and optical definition, which continued for several days. Otoliths from field-collected fish have also shown similar changes in daily increment properties during the juvenile stage, which may be an indicator of an environmental influence. The criteria for defining different increment types help to resolve our current age determination issues for late larval and early juvenile stage walleye pollock from the Gulf of Alaska.     

闽南渔场沿海仔稚鱼时空分布特征及影响因子

为探明闽南渔场沿海仔稚鱼时空分布特征及与环境因子的相关关系, 根据2022 年5 月(春季)、2022 年11月(秋季)、2023 年2 月(冬季)以及2023 年7 月(夏季)开展的4 个航次仔稚鱼调查资料, 研究该海域仔稚鱼的种类组成、数量分布、群落结构和多样性, 探讨闽南渔场海域的水文特征与仔稚鱼分布的相关关系。结果显示: (1) 4 个航次共采集仔稚鱼1114 尾, 隶属于9 目40 科87 种, 其中鲈形目(Perciformes)数量最多, 占研究海域仔稚鱼总数量的65.26%;夏季仔稚鱼丰度最高, 种类数最多, 秋季仔稚鱼丰度最低, 种类数最少; 各季度间优势种差异明显, 无公共优势种。(2) 闽南渔场沿海仔稚鱼群聚的组成各季节存在显著差异, 春−夏、夏−秋、秋−冬和冬−春的季节物种更替率依次为88.46%、98.15%、100.00%、92.11%。多样性分析结果显示, 仔稚鱼Margalef 丰富度指数(D)和Shannon-Wiener多样性指数(Hʹ)均夏季最高, 但Pielou 均匀度指数(Jʹ)冬季最高。(3) 仔稚鱼群落结构相似性分析表明, 春季、夏季和冬季各站位仔稚鱼群聚划分明显, 春季仔稚鱼群落可分为近岸类群和近海类群2 个群组, 夏季和冬季仔稚鱼群落均可分为近岸类群、近海I 类群和近海II 类群3 个群组。(4) 仔稚鱼时空分布与环境因子的相关性分析表明, 不同站位间盐度变化和季节间的温度变化是影响仔稚鱼时空分布的主要原因。本研究结果可为研究闽南渔场渔业资源的补充机制及制定渔业资源养护与管理措施提供科学依据。     

大连海区大泷六线鱼生物学指标的季节变化

2003年9月～2004年7月,分秋季、繁殖期、繁殖后、越冬后、春季、夏季6个时期在大连地区采集大泷六线鱼标本。各个时期分别采集雌雄标本20～30尾,规格约20cm。并于9月和10月采集幼鱼约50尾。测定样本的成熟系数、肥满度、肝指数、胃肠充塞度等生物学指标,分析了其生物学指标的季节变化规律及成幼鱼间的差别。     

Wind‐induced stock variation of the neon flying squid (Ommastrephes bartramii) winter–spring cohort in the subtropical North Pacific Ocean

Our examination of the neon flying squid (Ommastrephes bartramii) winter–spring cohort catch per unit effort (CPUE, an index of stock) revealed significant positive correlations with the interannual variations of observed chlorophyll‐a (Chl‐a) concentration and autumn–winter mixed layer depth (MLD) in the winter–spring feeding grounds of paralarvae and juveniles (130–170°E, 20–27°N). These correlations suggest the importance of integrated bottom‐up effects by the autumn–winter MLD for the neon flying squid stocks. However, the influence of autumn–winter MLD interannual variation in the forage availability for paralarvae and juveniles, i.e., particulate organic matter and zooplankton, has still been unclear. In this study, we use the lower trophic ecosystem model NEMURO, which uses the physical environmental data from the ocean reanalysis dataset obtained by the four‐dimensional variational (4DVAR) data assimilation method. The model‐based investigation enables us to clarify how the autumn–winter MLD controls the particulate organic matter and zooplankton abundance in the feeding grounds. Further, our investigation of the autumn–winter MLD interannual variation demonstrates that the stronger autumn wind in the feeding grounds develops a deeper mixed layer. Therefore, the deep mixed layer entrains nutrient‐rich water and enhances photosynthesis, which results in good feeding conditions for paralarvae and juveniles. Our results underline that the wind system interannual variation has critical roles on the winter–spring cohort of the neon flying squid stock.     

Effects of hydrologic regulation on icefish population dynamics,assemblage structure and fishery yield in Lake Nanyi,China

Stock dynamics and demographic parameters of a family of annual icefishes (Salangidae) were investigated in Lake Nanyi in eastern China before and after construction of irrigation infrastructure. After hydroregulation, two of four icefish species, a migratory species (Hemisalanx brachyrostralis) and a previously rare species (Neosalanx tangkahkeii) were absent from survey samples. The relative abundance of the remained icefish stocks changed greatly. The spring and autumn stocks of N. taihuensis increased from 9.9% and 1.7% to 74.8% and 4.8%, respectively, and N. oligodontis decreased from 84.8% to 20.4%. Total icefish density (CPUE) and yield doubled under the new hydrologic regime. Average adult body size and absolute fecundity of the three persistent icefish stocks decreased, and this could have resulted from slower rates of growth and development of larvae and juveniles in response to greater density of icefishes overall and more intense competition for planktonic food resources during summer and fall.     

Characterization of the quality of the gametes and sex steroid levels during spring and summer spawning events in pejerrey Odontesthes bonariensis reared under natural conditions of temperature and photoperiod

Pejerrey Odontesthes bonariensis spawning period takes place during the end of winter and spring and, depending on temperature conditions, during late summer and autumn. Nevertheless, the occurrence and quality of the summer–autumn spawning period have not been well documented and are not considered for aquaculture production. In this context, this study aimed to characterize the reproductive activity of pejerrey reared in captivity under natural conditions of temperature and photoperiod throughout a year in order to summarize the spawning quality of the two spawning periods. The present results showed that pejerrey might spawn from late winter to the end of the spring with a peak in October (mid‐spring) and, also during summer and early autumn, interrupted by a period of 56 days without spawning activity in between. The extension of both spawning periods was almost equal (67 and 69 days). Nevertheless, higher relative fecundity and larger egg size were observed during the first spawning period, associated with higher levels of oestradiol measured in females demonstrating that it is better than the second spawning. The fertilization rate was not affected throughout the reproductive periods. These differences in the reproductive parameters are discussed in order to design specific strategies to increase seed production.     

海州湾及其邻近海域鱼类群落结构冗余度

过度捕捞、环境污染等人类活动以及气候变化等影响着海洋鱼类群落动态及其稳定性。为深入研究海州湾海域鱼类群落结构及其变化,根据2011年、2013—2016年春、秋两季在该海域进行的渔业资源与环境调查数据,应用多元统计分析和结构冗余度分析方法,研究了海州湾海域春、秋季鱼类群落结构冗余度。结果显示,海州湾及邻近海域春、秋季鱼类均可划分为南北两个群落。春季北部群落的典型种包括方氏云鳚、细纹狮子鱼、黄鮟鱇和大泷六线鱼;南部群落的典型种为小黄鱼、短吻红舌鳎、方氏云鳚和星康吉鳗。秋季北部群落的典型种为棘绿鳍鱼、长蛇鲻和星康吉鳗;南部群落典型种包括短吻红舌鳎、棘头梅童鱼、鮸、矛尾虾虎鱼、小黄鱼和皮氏叫姑鱼。春、秋季鱼类群落响应单元数均为1,群落结构冗余度水平低;响应单元中种类与南、北鱼类群落典型种组成相似,表明海州湾春、秋季鱼类群落空间结构特征主要受方氏云鳚、细纹狮子鱼、小黄鱼、棘绿鳍鱼和长蛇鲻等少数种类决定。决定海州湾及邻近海域鱼类群落结构特征的可替代种类较少,当主要种类受损时,群落结构会发生较大变化,鱼类群落结构稳定性较低。     

Population dynamics of portunid crab <Emphasis Type="Italic">Charybdis bimaculata</Emphasis> in Ise Bay,central Japan

ABSTRACT:   The present study dealt with seasonal and interannual variations in the abundance and biomass, and spatio-temporal distributions of the portunid crab Charybdis bimaculata dominant in Ise Bay, central Japan. The abundance and biomass of the crab decreased in summer when the oxygen-poor water developed in central or inner parts of the bay, and then increased through new recruits from autumn (October–November) to the following spring (March–May) when the oxygen-poor water disappeared. Berried females were collected mainly from spring to autumn. Recruits were collected in any season. Particularly in winter, most recruits were located in the innermost part of the bay. According to the cohort separation based on size frequency distribution in carapace width of the crab specimens, the cohorts that were derived from spawning in spring to summer largely contributed to establishing and maintaining the benthic populations for the following year in the bay, whereas those from other seasons failed to recruit because of serious damage caused by the oxygen-poor water. Most crab individuals one year post hatch contributed to spawning and then died by the winter of the same year.     

Variation in DVM behaviour of juvenile and adult pearlside (Maurolicus muelleri) linked to feeding strategies and related predation risk

In the Norwegian fjord Masfjorden, different developmental stages of the mesopelagic planktivore Maurolicus muelleri form vertically separate sound scattering layers (SSLs) and in late autumn display different diel vertical migration (DVM) behaviour. Post‐larvae and juvenile fish perform normal crepuscular DVM, whereas the large majority of adults remain at depth throughout the diel period. In this study we examined the stomach contents of juvenile and adult fish caught at different times and depths during a 24‐h period in autumn. The different DVM behaviour of these two SSLs in addition to a shallow layer believed to be composed of post‐larvae is explained with a model for visual foraging in aquatic environments that uses gradients in vertical light intensity and copepod density and size as input variables. Field data revealed that vertically migrating juveniles distributed at a higher ambient light intensity and on average consumed 25 times more copepods than non‐migrating adult fish. The model showed that juveniles experienced a 15 times higher prey encounter rate and a higher level of predation risk than non‐migrating adults, and that the energetic benefits for post larvae and juveniles from prolonged feeding in a nearly constant and brighter environment outweigh the associated predation risk. The model also suggests that the visual detection range of piscivore predators is relatively more limited by the turbid surface water than that of their prey, which provide the post‐larva and juvenile life‐stages of M. muelleri a window of reduced visual predation near the surface.     

Comparative ecologies of domestic and naturalised rainbow trout in northern Lake Huron

Northern Lake Huron (Ontario, Canada) supports the largest concentration of freshwater salmonid cage culture farms in Canada and receives inputs of domestic‐strain rainbow trout (Oncorhynchus mykiss) through escapement. We assessed the potential effects of these domestic fish on the naturalised rainbow trout of this ecosystem by comparing their respective ecologies. Mature adults were sampled from spawning tributaries, primarily in spring, and to a lesser extent in fall. Fish of domestic origin comprised ~80% of rainbow trout sampled from sites near cage culture facilities but <20% of rainbow trout sampled from more distant sites. Domestic adults in spawning condition (gametes free‐flowing) were present in the spawning tributaries in both spring and fall sampling seasons, whereas naturalised fish in spawning condition were only observed in the spring. Domestic adults were younger and smaller (in length), appeared to have shorter lifespan and had a higher male to female ratio compared with their naturalised counterparts. Growth rates (change in length with age) of naturalised and domestic females in the wild were similar, but domestic males grew more slowly than naturalised males. Domestic females also produced smaller eggs than naturalised females. Food web positions (inferred from δ¹³C and δ¹⁵N) of domestic and naturalised fish were very similar but varied more strongly with body size in the former. Domestic‐strain rainbow trout of cage culture origin can survive, grow and attempt to spawn in northern Lake Huron and have the potential to compete for food, mates and spawning habitat with naturalised rainbow trout.     

长江口沿岸碎波带仔稚鱼分布的季节性变动

为进一步探明长江口沿岸碎波带仔稚鱼种类组成和数量分布的季节性变化特征,2006年11月至2007年10月,在长江口沿岸碎波带的13个站位用小型拖网(1 m×4 m,网目1 mm)共采集到仔稚鱼77种,隶属于13目27科63属。各季节出现仔稚鱼种数分别为37、20、13和7种。仔稚鱼是以暖温性种类占绝对优势,按生态类型划分,河口性和淡水性种类为主,其次为海洋性种类,洄游性种类最少。根据优势度曲线可看出,夏季优势种最突出,秋季优势种最不明显。夏季与秋季的共有种最多,均为27种;冬季与春季,冬季与秋季间的共有种最少,均为11种。从数量分布来看,冬季仔稚鱼数量最少,且分布较分散,春季数量有明显增加,夏季数量达最大值,且分布趋于集中。在低盐和淡水的站位St.4、St.5、St.7和St.10,形成了以刀鲚为主要种类的仔稚鱼密集区,平均密度高达2 729尾/站。     

The source of autumn and spring downstream migrating juvenile Atlantic salmon in a small lowland river

Over 3 years, 32,444 age‐0 group Atlantic salmon (Salmo salar) parr tagged with passive integrated transponder tags throughout the River Frome catchment were assigned to one of three groups, nonmigrants, autumn migrants and spring smolts, depending on the detection and the timing of detection at downstream tag readers (situated 8.6 km above the tidal limit). We examined the effect of density at the time of tagging (n·m^?2), distance upstream from the tidal limit (km), fish length (mm), Fulton condition index, habitat type (divided into two types, main river and carrier), days after 1 September that each fish was tagged and year (replication) on the proportions of fish in each of the migration groups. Distance upstream from tidal limit was strongly negatively related to the proportion of autumn migrants and positively related to the proportion of spring smolts. Nonmigrants had a lower average body size than migrants, although there were no differences in the sizes of autumn migrants and spring smolts in September prior to migration. Fish density had no effect on migration strategy. A lower proportion of fish migrated as autumn migrants from the smaller carrier habitats than the main river channel. There is some evidence that those parr destined to become autumn migrants underwent a lower mortality rate during September before tagging than those destined to become spring migrants indicating possible physiological or behavioural differences between these two groups of fish at that time. More research into the factors responsible for initiating the autumn migration is required.