东海近海蟹笼网目尺寸对三疣梭子蟹的选择性

不断壮大的东海近海笼壶渔业对三疣梭子蟹（Portunus trituberculatus）等甲壳类资源造成了巨大的压力，实施养护幼蟹的管理措施已成为渔业管理者和生产者的共同呼声。本研究通过海上对比试验，分析了放大网目尺寸对蟹笼渔获效率的影响，运用SELECT模型估算了蟹笼对三疣梭子蟹的尺寸选择性，结合混合影响模型探讨了作业时间和可捕群体对选择性分析的影响。结果显示，对照蟹笼（网目尺寸32.0 mm）与试验蟹笼（网目尺寸分别为52.3 mm和59.7 mm）的三疣梭子蟹渔获甲宽分布存在显著性差异；SELECT模型拟合结果显示试验蟹笼与对照蟹笼的相对作业强度无显著性差异，网目尺寸分别为52.3 mm和59.7 mm的试验蟹笼对三疣梭子蟹的50%选择甲宽（CW₅₀）分别为86.9 mm和90.9 mm，选择范围分别为15.9 mm和9.2 mm。试验蟹笼的CW₅₀远未达到浙江省等当前的最小可捕尺寸规定，表明蟹笼渔业中仅依靠放大网目尺寸可能难以实现幼蟹的有效释放。结果分析显示，在此次试验中作业时间和可捕群体的数量对蟹笼的选择性没有显著性影响。     

iTRAQ‐based identification of differentially expressed proteins related to growth in the swimming crab,Portunus trituberculatus

The swimming crab, Portunus trituberculatus, is an important farmed species in China, and it has been studied extensively, which requires more information on its genetic background. To date, information on the proteomics of P. trituberculatus is scarce. In this study, we used isobaric tags for relative and absolute quantitation (iTRAQ)‐based proteomics to investigate growth regulation in P. trituberculatus. Total proteins were isolated from five tissues (eyestalk, gill, heart, hepatopancreas and muscle). Equal quantities of protein from each tissue were pooled at the proteome level using the iTRAQ method. A total of 961 proteins were identified using liquid chromatography coupled with tandem mass spectrometry and de novo sequencing data. Using a 1.2‐fold change in expression as a physiologically significant benchmark, 30 differentially expressed proteins (DEPs) were found to undergo differential expression related to the growth of P. trituberculatus, and most of the growth‐related proteins, including those involved in metabolism, immune responses, DNA duplication and protein synthesis, were upregulated, indicating that conservation of energy is an important strategy to cope with growth. There was a high consistency between the expression levels determined using iTRAQ and mRNA, highlighting the high reproducibility of our proteomic approach and its great value in elucidating the molecular mechanisms of P. trituberculatus.     

Abiotic and biotic factors affecting recruitment variability of walleye pollock (Theragra chalcogramma) off the Pacific coast of Hokkaido,Japan

Abiotic and biotic factors affecting the recruitment variability of the Japanese Pacific stock (JPS) of walleye pollock (Theragra chalcogramma) were examined using a bivariate regression and multivariate combined model. Of the abiotic variables around Funka Bay (spawning ground), February sea surface temperature (SST) and wind direction index showed significant bivariate relationships with recruitment. February SST was positively related to recruitment, suggesting that warmer water temperature in February favors JPS recruitment. On the other hand, the relationship between February wind direction index and recruitment predicts high JPS recruitment under predominant northwest winds in February. For the biotic variables in the Doto area (nursery ground), significant and negative bivariate relationships with recruitment were observed for catch per unit effort of Kamchatka flounder (Atheresthes evermanni), Pacific cod (Gadus macrocephalus), and walleye pollock, implying an important impact of predation by these groundfishes on JPS recruitment. The overall model incorporating these abiotic and biotic factors successfully reproduced the variability in JPS recruitment. Temperature and wind conditions around the spawning ground along with predator condition in the nursery ground appear to play a dominant role in the recruitment dynamics of JPS. Based on these results and prior knowledge, we propose a new hypothesis to explain the processes controlling JPS recruitment.     

致急性肝胰腺坏死病副溶血弧菌(VpAHPND)自然感染三疣梭子蟹

近年来包括急性肝胰腺坏死病(AHPND)在内的多种新发疫病的流行,使我国甲壳类养殖业遭受了严重的经济损失。为了筛查导致山东潍坊某养殖场中一虾蟹混养池塘内患病三疣梭子蟹感染的可能病原,本研究采用分子生物学检测方法,对三疣梭子蟹样品进行了白斑综合征病毒(WSSV)、传染性皮下及造血组织坏死病毒(IHHNV)、虾血细胞虹彩病毒(SHIV)、致急性肝胰腺坏死病副溶血孤菌(Vp_(AHPND))、虾肝肠胞虫(EHP)、偷死野田村病毒(CMNV)、黄头病毒(YHV)和肝胰腺细小病毒(HPV)等8种病原的检测,并对样品进行了组织病理和原位杂交分析。分子生物学检测结果显示,患病三疣梭子蟹样品呈Vp_(AHPND)阳性,而呈现WSSV、IHHNV、SHIV、EHP、CMNV、YHV和HPV阴性。对样品进行Vp_(AHPND)套式PCR第二轮扩增产物的序列测定、比对和进化树分析,结果显示,扩增产物序列与致病副溶血弧菌质粒上pirA~(vp)毒力基因片段具有99%的同源性,该序列与已报道的多个致病副溶血弧菌PirA聚在进化树的同一主分支上。组织病理学分析显示,患病三疣梭子蟹的肝胰腺小管上皮细胞坏死,心肌纤维呈溶解样病变,鳃丝上皮柱突细胞明显坏死,胸神经节的神经细胞损伤严重,并且这些组织中还可见大量的细胞核固缩现象;原位杂交结果显示,肝胰腺、心肌、鳃组织及胸神经节中的病变部位均存在Vp_(AHPND)探针的蓝紫色杂交信号。以上表明,虾蟹混养池塘中三疣梭子蟹在自然状态下感染了Vp_(AHPND),并导致肝胰腺、心肌、鳃和胸神经节发生了严重病理损伤。本研究首次在养殖三疣梭子蟹中检测到Vp_(AHPND)感染并揭示了感染所致的病理变化,相关结果为揭示Vp_(AHPND)自然宿主种类和养殖三疣梭子蟹病害防控提供了基础信息。     

Effects of supplementation of decapod zoea to Artemia basal diet on fatty acid composition and digestive gland histology in common octopus (Octopus vulgaris) paralarvae

The present study aimed to evaluate the effect of the supplementation of different crab zoeas to enriched Artemia basal diet for Octopus vulgaris paralarvae during the first month of life. Paralarvae were fed using enriched Artemia nauplii alone and Artemia co‐fed either first zoea stages of Grapsus adscensionis or Plagusia depressa. The experiment was carried out over a period of 28 days, in 0.12 m³ tanks with a flow‐through rearing system. Growth in dry weight as well as mantle length and width were assessed weekly. Additionally, prey and paralarvae fatty acid composition and digestive gland (DG) histology were evaluated. Addition of low amounts of crab zoeas (approx. 100 indv. L^?1 day^?1) provided during critical life stages of O. vulgaris proved to be good enough to improve paralarvae growth and survival in comparison with those fed exclusively on enriched Artemia. These results were supported by the finding of a higher number of glycoprotein absorption vacuoles in the DG from paralarvae co‐fed crab zoeas, suggesting a higher feeding activity. In addition, fatty acid analysis of crab zoea showed that these are good sources of dietary arachidonic and eicosapentaenoic acids during the octopus planktonic life stage, whereas the low docosahexaenoic (DHA) content suggests the use of additional DHA sources or higher zoea densities to meet paralarvae nutritional demand to carry out a successful metamorphosis to benthic life.     

莱州湾4种大型甲壳类的空间与营养生态位

根据2010—2019年夏季莱州湾底拖网调查数据,研究了4种大型甲壳类(中国明对虾、三疣梭子蟹、日本蟳和口虾蛄)的优势度、种间联结、空间生态位特征,并应用碳氮稳定同位素数据分析了4种大型甲壳类的营养级、营养生态位与摄食来源。结果显示,口虾蛄、日本蟳是目前莱州湾夏季甲壳类最主要的优势种,放流种类中国明对虾、三疣梭子蟹为群落的重要种;4种大型甲壳类的种间联结性不强,显著正联结主要出现于中国明对虾与其他三者之间;日本蟳空间生态位宽度最高(2.45),口虾蛄(2.13)次之,中国明对虾(1.92)和三疣梭子蟹(1.93)较低;生态位重叠较高主要发生于中国明对虾与其他3种之间;4种大型甲壳类营养级相近(3.02～3.28),中国明对虾生态位总面积最大,三疣梭子蟹与日本蟳、口虾蛄的生态位总面积相近,三疣梭子蟹和日本蟳的营养生态位重叠较高;摄食来源分析表明,中国明对虾摄食双壳类比例更高,其他3种摄食来源同质化程度较高。目前莱州湾三疣梭子蟹和中国明对虾的优势度低于口虾蛄和日本蟳,表明增殖放流虽然扩大了三疣梭子蟹和中国明对虾的种群规模,但尚未较大程度改变甲壳类群落结构。综合4种甲壳类的群落地位、种间联结性、空间生态位宽度与重叠、营养级与营养生态位以及摄食来源的研究结果,中国明对虾与其他三者竞争相对较小,而三疣梭子蟹与日本蟳、口虾蛄竞争较大。为最大程度发挥增殖效益,建议在确定放流地点和放流数量时,应着重考虑相近生态位物种对放流物种的竞争和限制。     

池塘养殖三疣梭子蟹的生长规律

为探讨池塘养殖三疣梭子蟹的生长规律和雌雄差异，本研究对1～6月龄池塘养殖三疣梭子蟹各生长指标进行了比较分析，并采用Logistic模型分别拟合三疣梭子蟹的体重(BW)、体长(BL)、体高(BH)、全甲宽(FCW)、甲宽(CW)、大螯长节长(MLC)、大螯不动指长(FFLC)、第一步足长节长(MLFP)等8个形态性状的生长特征。结果显示，三疣梭子蟹雌性和雄性的生长存在差异，早期雄性生长较快，后期雌性生长较快，而雌雄混合分析介于二者之间。三疣梭子蟹各生长性状的Logistic模型拟合结果显示，除雌性MLC和MLFP以及雌雄混合分析的MLFP之外，其余性状R²均达到0.990以上；雌性和雄性体质量的极限生长值分别为290.27和195.91g，快速生长区间分别为2.74～5.10月龄和2.33～4.14月龄，拐点分别为3.92和3.24月龄。研究表明，三疣梭子蟹的生长过程均符合“慢-快-慢”的特征，雄性比雌性更早进入快速生长期，但是快速生长期的持续时间不及雌性。本研究对三疣梭子蟹不同生长指标的规律特征，以及各指标在混合养殖条件下雌性和雄性的优势阶段进行了研究，为实现三疣...     

莱州湾“伏休”结束前三疣梭子蟹的资源状况及其分布特征

根据2010—2017年莱州湾"伏休"结束前底拖网调查资料,通过轮廓系数法对莱州湾三疣梭子蟹资源的时空分布特征进行了研究,并结合放流回捕资料对莱州湾三疣梭子蟹资源状况提出了建议。结果显示,在空间分布上,三疣梭子蟹南部资源明显优于北部;依据Rousseeuw质量指数分为3组,分别为近岸组、远岸组和深海组,分组评估合理,平均轮廓系数为0.34,组内相似度较高,聚类效果较好;从时间变化上,三疣梭子蟹资源具有明显的年际波动性,依据Rousseeuw质量指数分为3组,分别为较好组、一般组和较差组,分组评估合理,平均轮廓系数为0.15,组内相似度较低,聚类效果较差。另外,空间分组的Pearson相关性分析结果表明,三疣梭子蟹资源状况与"伏休"结束前近岸组资源密切相关;时间分组的SIMPER分析结果同样显示,三疣梭子蟹资源状况主要取决于"伏休"结束前的近岸资源。因此,"伏休"结束前三疣梭子蟹近岸资源的管理与保护对于三疣梭子蟹资源的影响至关重要,建议在实施三疣梭子蟹增殖放流时,不仅要保持增殖的规模,还应重点关注前期资源的保护与管理,从而有效增加近岸资源,进一步实现三疣梭子蟹增殖放流修复的意义。     

Improvement of larval rearing technique for mass seed production of snow crab <Emphasis Type="Italic">Chionoecetes opilio</Emphasis>

Larval rearing experiments were conducted to examine the potential for mass seed production of the snow crab Chionoecetes opilio using a total of eight 20-kL tanks. Tanks were equipped with agitators, which move the water using a rectangular blade to prevent the zoeas sinking to the bottom of the tank. Larval rearing water was treated with sodium nifurstyrenate once a week to reduce the chance of larval infection by pathogenic bacteria. Zo eas were fed with rotifers and Artemia nauplii. A total of 122 830 megalops and 16 660 first-stage crabs were produced. Thus, the potential for mass seed production of snow crab was determined. Survival rates up to the megalopal stage were high in tanks with a feeding regime that fed rotifers to larvae through an entire zoeal stage. This study also describes the fatty acid composition of snow crab larvae. It revealed that the first zoeas had a high DHA content and DHA/EPA ratio, but these values significantly decreased in the second stage zoeas and megalops. Improving the DHA content and/or DHA/EPA ratio of larvae should be important in studies on mass seed production technology of the snow crab.     

Identification of quantitative trait loci for growth‐related traits in the swimming crab Portunus trituberculatus

The swimming crab (Portunus trituberculatus) is an economically important species in Asian aquaculture. Implementing growth‐related traits of P. trituberculatus into genetic breeding programmes is an ongoing effort. We used a previously published genetic linkage map of P. trituberculatus, containing 55 simple sequence repeat (SSR) markers and 172 amplified fragment length polymorphism (AFLP) techniques to map quantitative trait loci (QTL) for growth‐related traits in a single full sibling F₂ family. Ten growth‐related traits were measured for QTL mapping. Composite interval mapping identified 9 QTL on the female map and 16 on the male map. Individual QTL with additive effects explained 11–38% of the phenotypic variance for various traits using the female parent's map, and from 1% to 21% using the male parent's map. Two QTL explaining a large percentage of variation in body weight were detected on chromosome 17 on the female map, and on chromosome 16 on the male map, and contributed 38% and 18% of the phenotypic variance respectively. This is the first study to report the detection and positioning of major QTL affecting growth in a true crab species (Brachyura). The mapping of growth‐related QTL in this study raises the possibility of improving the growth of P. trituberculatus through marker‐assisted selection.     

Effect of environmental factors,especially hypoxia and typhoons,on recruitment of the gazami crab <Emphasis Type="Italic">Portunus trituberculatus</Emphasis> in Osaka Bay,Japan

Important crustacean fisheries occur in semi-enclosed seas. These fisheries can be strongly affected by intense exploitation and episodic anthropogenic and climatic events, but the effects of such events remain largely uninvestigated. To assess the influence of such factors, we examined dredge catch data on the gazami crab Portunus trituberculatus in Osaka Bay, Japan from 1984 to 2008 and investigated various associated environmental factors. There were five peak monthly catches during the study period, which typically occurred in August or November. Relative abundance (measured as catch per unit effort) in August was positively associated with previous recruitments to the fishery, typhoon frequency, and dissolved oxygen saturation during the juvenile period. In comparison, relative abundance in November was strongly correlated with the number of typhoons and was also positively associated with dissolved oxygen levels in the bottom water. The results of our multi-decadal study suggest that hypoxia is a principal agent of mortality for juvenile crabs and that normoxia in the nursery habitats is a necessary condition for the successful recruitment of individuals into the adult population. The positive influence of typhoons on recruitment is probably due increased mixing in stratified coastal waters, which disrupts the persistent hypoxia in bottom waters, but other unknown processes may also contribute to favorable recruitments.     

Ovarian development and nutritional quality changes of the wild‐caught Portunus trituberculatus during the artificial fattening period

A female swimming crab (Portunus trituberculatus) with fully developed ovaries is considered one of the most nutritious types of seafood. The fishing yield of P. trituberculatus in China has always been high; however, its economic value has been low and unreliable due to poor ovarian development and low nutritional value. Artificial fattening is an effective way to improve the value of wild‐caught crabs, and this study focused on analysing the ovarian development and nutritional quality of the female P. trituberculatus during an artificial fattening period. Therefore, this study provides scientific evidence on the effects of artificial fattening on female P. trituberculatus and can guide the development of nutritional quality regulations for wild‐caught female crabs during the fattening process. The results showed that the ovaries of the wild female P. trituberculatus developed gradually. The ovarian morphology became bulkier, while the gonadosomatic index (GSI) and total edible yield (TEY) were significantly improved after artificial fattening. Significant changes in the nutritional components of the edible tissues were observed, and the moisture content in the ovaries and hepatopancreas decreased continually, while both the protein and fat content in the ovaries significantly increased. Moreover, the fat content in the hepatopancreas significantly increased. The saturated fatty acids(ΣSFA) in the ovaries and hepatopancreas had an increasing trend after fattening, while ΣPUFA and Σn‐3PUFA first decreased and then increased. In contrast, the ratio of Σn‐3PUFA to Σn‐6PUFA decreased steadily. However, the fatty acid composition of the muscles did not change significantly. The levels of all the amino acids increased continuously during the fattening process, and EAA increased significantly in the early stages of the fattening period. Consequently, all amino acids became nonlimiting amino acids after fattening. Furthermore, the ratio of EAA/NEAA in the ovaries increased continually until the end of the fattening period. On the other hand, the fatness and TEY increased significantly after artificial fattening. In addition, the nutritional value significantly improved with the exception of the high‐quality fatty acids in the ovaries and hepatopancreas, which were slightly lower in both.     

Comparison of immune responses and antioxidant status of different generations of growth‐selected Portunus trituberculatus families

The purpose of this study was to investigate the effects of inbreeding on the immune responses and antioxidant status of Portunus trituberculatus juveniles. Results showed that inbreeding affected the total haemocyte count, and phagocytic, pro‐phenoloxidase (propo), phenoloxidase and antibacterial activities decreased after the seventh generation. Antioxidant status showed a similar pattern: total antioxidant capacity, superoxide dismutase (SOD) activity and GSH/GSSG in the cell‐free haemolymph and hepatopancreas decreased, while catalase activity in the cell‐free haemolymph increased (P < 0.05). There were no significant differences in α₂‐macroglobulin and bacteriolytic activities in the cell‐free haemolymph and glutathione peroxidase activity in the cell‐free haemolymph and hepatopancreas among nine inbreeding generations. Gene expression levels of proPO and crustin in haemocytes and SOD in haemocytes and hepatopancreas also decreased significantly as the inbreeding generations increased. The results suggest that a high level of inbreeding could severely reduce the physiological health of P. trituberculatus. Our obtained data would be particularly useful for P. trituberculatus breeding programmes.     

Effects of co‐supply ratios of swimming crab Portunus trituberculatus zoeae and Artemia on survival and growth of East Asian common octopus Octopus sinensis paralarvae under an upwelling culture system

Despite recent advances in culture technology for East Asian common octopus Octopus sinensis paralarvae using upwelling systems, securing suitable feed for the paralarvae is an unresolved issue. The zoea of the swimming crab Portunus trituberculatus is a good candidate for paralarval feed because of the high fecundity of the adult females. To investigate the effects of supplying P. trituberculatus zoeae and their feeding method on paralarvae, we cultured paralarvae with supplying different combination ratios of zoeae and Artemia (10:0, 7:3, 5:5, 3:7 and 0:10), and with or without supplementing rotifers using small‐scale (3‐L) upwelling systems. Paralarval survival rate and growth were improved when zoeae were supplied as the main feed, but reduced when the proportion of Artemia exceeded half the whole preys. Supplementing rotifers did not affect the paralarval survival and growth. Subsequently, paralarvae were cultured by supplying zoeae (partially augmented by Artemia) using three large (1‐kl) upwelling systems to assess their feeding effectiveness in juvenile octopus production. Paralarvae could be cultured at high survival rates of 77.1 ± 5.1% to reach benthic juveniles at 23 days after hatching. In conclusion, supplying P. trituberculatus zoeae augmented with Artemia under an upwelling culture system has great potential for juvenile octopus production.     

三疣梭子蟹受精卵离体孵化技术

为了探究三疣梭子蟹受精卵的离体孵化技术及效果，本研究先后开展了受精卵块最适分离液种类及作用条件的筛选、分离液处理不同发育期受精卵离体孵化的差异、分离液处理对受精卵卵膜的结构影响，及分离液处理受精卵对孵化后幼体活力的影响实验。结果显示，木瓜蛋白酶是一种较为理想的分离液，在浓度为0.09 g/mL，分离时间30 min时，分离率可达到99%以上；经过分离液处理后的各期受精卵均能孵化出幼体，卵内溞状幼体期离体胚胎孵化率最高，为89.0%±3.3%，未经处理的对照组为70.0%±4.8%；卵裂期离体胚胎孵化率最低，为58.0%±3.9%，对照组为31.0%±2.3%，与对照组相比，处理组的孵化率明显提高。透射电镜结果显示，经过分离液处理的受精卵卵膜结构疏松，且厚度降低，符合处理组孵化率增加这一现象，干露、福尔马林溶液胁迫和行为学测试对不同处理组的幼体进行质量评价的结果显示，处理组和对照组幼体活力无显著差异。研究表明，实验所获得的分离液可以有效提高三疣梭子蟹受精卵的分离率和孵化率，且不影响幼体质量，可为三疣梭子蟹及其他甲壳动物受精卵的离体孵化提供参考。本研究可为三疣梭子蟹的苗种繁育提供新的技术手段，也将为基因编辑辅助育种等技术的实施奠定基础。     

Isolation,characterization and virulence of Mesanophrys sp. (Ciliophora: Orchitophryidae) in farmed swimming crab (Portunus trituberculatus) in eastern China

A disease outbreak occurred in swimming crab (Portunus trituberculatus) farmed in eastern China, with a mortality rate of more than 80%. To further investigate the characteristics and pathogenesis, we reported isolation, characterization and virulence of the causative agent of this disease from 10 sick crabs. Histopathological observation found that multiple tissues, especially haemolymph, contained lots of ciliates. The ciliate was isolated and cultured in vitro, and molecular and morphological studies were done. The results showed that SSU rDNA and LSU rDNA sequences of the ciliate were similar to Mesanophrys ciliates (>96.81%), while ITS1-5.8s-ITS2 sequence was similar to Mesanophrys pugettensis (95.37%) and identical to Orchitophrya stellarum (100%). Furthermore, the results of the morphological study confirmed that the ciliate was similar to Mesanophrys ciliates and O. stellarum cultured in supportive media, but different from O. stellarum cultured in living sperm cells of starfish (Leptasterias spp.). Also, the growth of the ciliate did not interfere with light, which was different from O. stellarum. Accordingly, the ciliate was classified as genus Mesanophrys and temporarily named as Mesanophrys sp. In addition, experimental infection confirmed that Mesanophrys sp. was the pathogen that infected farmed crabs. In summary, Mesanophrys sp. was first isolated and characterized in P. trituberculatus.     

三疣梭子蟹心激肽基因克隆及在低盐适应中的功能验证

采用RACE技术克隆获得三疣梭子蟹(Portunus trituberculatus)心激肽(CCAP)基因。该基因全长606 bp, 5￠端非编码区72bp,3￠端非编码区108bp,开放阅读框426bp,编码141个氨基酸,预测分子量15.6kD,理论等电点9.55。同源性分析表明,三疣梭子蟹CCAP与拟穴青蟹(Scylla paramamosain)和蓝蟹(Callinectes sapidus)的CCAP同源性较高,分别为85%和82%。系统进化树分析显示,三疣梭子蟹与蓝蟹首先聚为一支,之后再与拟穴青蟹相聚。组织表达分析发现, CCAP基因在胸神经节中的相对表达量最高,其次是脑和眼柄组织。通过分析CCAP基因在低盐胁迫过程中的表达规律发现,低盐可显著改变CCAP在胸神经节中的表达模式,在24 h, 48 h和72 h实验组的表达量显著高于对照组(P0.05),分别为对照组的1.73, 2.16和2.19倍。体外注射CCAP多肽可降低三疣梭子蟹在低盐条件下的死亡率,并诱发钠钾ATP酶(Na~+/K~+-ATPase)和V型ATP酶(V-ATPase)酶活力显著提高。本实验结果暗示CCAP通过调控Na~+/K~+-ATPase和V-ATPase活力以达到盐度适应的作用。     

A biophysical model to assess the trade‐off between larval recruitment and catch in southern Australia's largest prawn fishery

Data from stock assessment surveys, published research and climate sensors were linked to model the interaction between fishing, physical‐oceanographic processes and spatial patterns of larval settlement for western king prawn [Penaeus (Melicertus) latisulcatus]. This information was used to evaluate the trade‐off between larval recruitment and catch during fishing periods that demand high prices but coincide with spawning. Total rates of larval settlement were maximized when tidal currents and atmospheric physical‐forcing components were coupled with simulations of larval swimming behaviour under average gulf temperatures. Average gulf temperatures sustained longer larval durations and increased larval settlement rates by over 12% compared with warmer gulf conditions simulated under a scenario of global warming. Reproductive data coupled with outputs from the biophysical model identified consistent inter‐annual patterns in the areas contributing to larval settlement success. Areas located in the north‐east, and central‐west of the fishery, consistently contributed to over 40% of all larvae reaching a settlement in each year. Harvest sensitivity analyses indicated that changes in the spatial patterns of pre‐Christmas fishing could lead to improvements in overall rates of the larval settlement while maintaining or improving the levels of catch. Future studies to refine the model inputs relating to physical processes, larval behaviour and mortality rates for P. latisulcatus coupled with surveys of juvenile prawn abundance to ground truth the modelled predictions, would allow stock recruitment relationships to be more closely examined and inform adaptive management of the fishery in the future.     

Photoperiod affects the survival rate but not the development of larval swimming crab Portunus trituberculatus

Photoperiod is a crucial environmental factor affecting the survival and development of crustacean larvae. The full-spectrum light-emitting diodes (LEDs) were used as light sources to investigate the effect of five photoperiods, i.e., 0 L:24D (constant darkness), 6 L:18D (6 h photophase), 12 L:12D (12 h photophase), 18 L:6D (18 h photophase), and 24 L:0D (constant light) on the survival and development of the swimming crab Portunus trituberculatus larvae (from zoea I to juvenile crab). Natural photoperiod (ambient) was used as a control group. Each treatment had four replicates (n?=?4, 100 larvae per replicate). The experiment lasted 20 days when all the larvae died or metamorphosed into juvenile crabs. The results revealed that the P. trituberculatus could not metamorphose into juvenile crab under constant darkness, 6 h photophase, and constant light, and all the larvae died in zoeal III, zoeal IV, and zoeal IV stage, respectively. The highest survival and the shortest developmental duration of larvae were found in the 12 h photophase group (1.75%, 16.80 d) but were not statistically different from those reared in the 18 h photophase group (0.75%, 17.00 d) and natural photoperiod (0.25%, 18.90 d). The above results indicated that full-spectrum LEDs could be a considerable alternation for natural light, and the optimal photoperiod for P. trituberculatus larvae is 12–18 h photophase.

     

The influence of hydrology on the recruitment of brown trout in an Alpine river,the Ybbs River,Austria

Abstract – We monitored yearly recruitment (1997–2008) of brown trout (Salmo trutta) in a fourth‐order Austrian Alpine river. The relative proportion of recruits to adult fish varied strongly among years (5.6–66.4%). These proportions were strongly correlated with specific flow patterns. High flows before and during the spawning period were positively correlated with recruitment, whereas high flows during incubation and emergence were negatively correlated with recruitment success. Unsteady flow modelling supported a causal hypothesis for these relationships in demonstrating that discharges > 30 m³·s^?1 resulted in substantial sediment motion (erosion and deposition) in suitable spawning areas within the study stretch.