Control of dissolved oxygen levels of water in net pens for fish farming by a microscopic bubble generating system

ABSTRACT:   A microscopic bubble generating system (MBGS) has been developed to control dissolved oxygen (DO) levels suitable for fish farming. The MBGS has been tested to confirm its capability in net pens. Water conditions in a fish farm were monitored every two hours from June to October 2004 by setting an online vertical profiling system (OVPS) close to the net pen. DO in the net pen water decreased to physiologically stressful levels for the fish during the night (4.84–5.51 mg/L), while the DO was kept in saturated conditions during the day, due to oxygen supply from phytoplankton. The MBGS was operated from the evening to the morning of the next day for 16 h, to successfully create DO-saturated conditions in the net pen water at night. By using microscopic bubbles during the warm seasons, DO levels in the net pen water could be improved to a level suitable for fish farming. However, the low DO levels (<5.0 mg/L) of the bottom water occasionally extended to the net pen layers, despite the supply of microscopic bubbles to the water. To maintain the DO of the net pen water at levels suitable for fish farming, DO supply to the net pen water and the bottom water needs to be increased, and the organically enriched sediment just below the net pens needs to be treated.     

Effects of 17/0 circle hooks and bait on fish catches in a Southern Atlantic swordfish longline fishery

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Balancing conservation and recreational fishery objectives for a threatened fish species,the Murray cod,Maccullochella peelii

Murray cod Maccullochella peelii (Mitchell) is a large, iconic Australian fish species targeted by anglers but also listed as nationally threatened. A consultative process that included conservation and fishery interests helped to develop a population model for this species and agree on management scenarios to be tested. The modelled scenarios illustrated that threats to populations (risk of decline) can be substantially reduced and catch rates increased through harvest slot length limits (HSLL) rather than minimum legal limits (MLL). A 600‐ to 1000‐mm HSLL provided lower risk of decline and greater catch rates than the existing 500‐mm MLL, but better results were achieved with a 400‐ to 600‐mm HSLL. Importantly, a range of other impacts (fish kills, stocking, thermal impacts, larval mortalities, habitat changes) were recognised and incorporated. This study provides an example of the utility of a population model to improve management decision‐making for both conservation and fishery objectives.     

梭子蟹定置三重刺网设计与试验

根据捕捞目标的生物学习性和体型特征,设计了一种捕捞三疣梭子蟹(Portunus trituberculatus)的专用定置三重刺网并进行了生产试验。所设计的刺网主尺度为50.00 m×1.08 m,上纲长50.00 m,下纲长66.00 m;内网衣规格为1 200目×18.5目,目大120 mm;外网衣规格为200目×2.5目,目大500 mm。2015年9月4—26日在莱州湾渔场进行了生产试验。结果表明,新刺网所捕获的三疣梭子蟹平均体重为175.69 g,单位捕捞努力量渔获量(CPUE)为1.61 kg/(片·次),主捕率高,其中梭子蟹产量占总渔获量的99.31%。新设计的刺网,下纲比上纲长32%,网衣底部较松弛,提高了网衣对梭子蟹的缠络性能,因而提高了捕捞效率;内网衣网目较大,利于释放幼鱼,网高较低,减小了捕获中上层鱼类的几率,因此,兼捕率较低,有利于渔业资源的保护。     

Feasibility of a single-species quota system for management of the Malaysian multispecies purse-seine fishery

Malaysian fisheries employ multiple measures to improve management; however, not all are well-suited to the multispecies fisheries. As part of a pilot project, an individual quota system was introduced for the purse-seine fishery off the East Coast of Peninsular Malaysia (ECPM), but no assessment of this particular measure nor the feasibly of its implementation has been confirmed. Therefore, this study analysed spatial and temporal patterns of purse-seine fishing, by collecting catch composition data per landing and its fishing ground within three period fishery surveys between August 2017 and September 2018 at six different landing sites. Similarity and cluster analysis examined species composition and diversity to determine the feasibility of implementing a single-species quota system in this multispecies fishery. Some overlapped of indices results and minor difference in catch composition were found due to changes in spatial and temporal fishing activities. However, no specific spatial or temporal patterns were discernible as structuring the fishing grounds used by purse-seiners. The absence of patterns, using the available data, might be attributable to huge species aggregations and widely distributed and homogenously mixed fish stocks. Thus, it is likely impractical to manage species individually in such a multispecies fishery.     

Selectivity estimates for Amblygaster sirm (Clupeidae) in the small-meshed gill net fishery on the west coast of Sri Lanka

Selectivity of Amblygaster sirm by gill nets of seven mesh sizes ranging from 2.3 to 3.8 cm stretched mesh was studied for a period of 12 months in the coastal waters off Negombo on the west coast of Sri Lanka. The size range of fish caught was 9.0–22.0 cm. Selection by mesh sizes smaller than 3.0 cm was towards the lower end of the selection curve.

Estimated values for selection factors ranged from 5.11 to 6.03 and those for optimum selection lengths varied from 12.9 to 19.7 cm. The highest selection factor was observed for 2.9 cm mesh, probably due to wedging of larger individuals in this mesh.     

A decision support system for setting legal minimum lengths of fish

Abstract  The use of legal minimum lengths is one of the oldest forms of regulation in fisheries management. Management objectives using minimum legal lengths are varied, often conflicting and generally poorly communicated. This paper introduces a decision support system that will assist fisheries managers in determining optimal legal minimum lengths. The system uses multi-criteria decision analysis to enable the integration of objective scientific and biological information into a system that assesses the success of any potential length limit in achieving each of the management objectives. The system can also document trade-offs between options that achieve management objectives and short-term socio-economic impacts. The decision support system is demonstrated using 13 commercially and recreationally important coastal species from New South Wales, Australia.     

New fish resources of reservoirs in Sri Lanka: Feasibility of introduction of a subsidiary gillnet fishery for minor cyprinids

The existing commercial fishery of the Sri Lankan reservoirs is a gillnet fishery, which is almost mono-specific, based on the exotic, Oreochromis mossambicus (Peters). The reservoirs are also known to harbour significant populations of indigenous, minor cyprinids. In this paper, results of experimental surveys with gillnets of different mesh sizes in five reservoirs, carried out to evaluate the feasibility of exploiting these untapped resources, are presented. It is apparent that there are differences in the minor cyprinid fauna in the reservoirs. The selection curves for each minor cyprinid species and the size and proportion of landings of minor cyprinids and O. mossambicus indicate that a subsidiary gillnet fishery of 15–20 mm mesh size could be introduced without affecting the existing O.mossambicus fishery.     

Intensive rearing system for fish larvae research II: Artemia hatching and enriching system

Live food such as Artemia is considered to be an essential part of any marine finfish hatchery. Standard methods were developed for hatching and enhancing the nutritional value of the Artemia nauplii by using different enrichment products. Although there is a variety of commercially available products in the market, further research on more specific enrichments for solving specific nutritional deficiencies in fish larvae is still required. A simple, compact and reliable experimental system was developed for these nutritional experiments. The system was built as a compact, all-in-one system with eight 50-l conical tanks in a water bath. The system reduces variation between the replicates (tanks), otherwise resulting from individual heaters and aeration. It reduces the manpower and time needed for harvesting and to re-establish the system on a daily basis by the ability to harvest, wash and refill all the tanks at the same time with the same volume of water. The system has been used for a variety of experiments, comparing commercial and experimental enrichments, bacterial monitoring and evaluation of different Artemia procedures.     

A system for automatic recording of fish tagged with coded acoustic transmitters

A telemetry system designed to automatically record the presence and swimming direction of fish tagged with coded acoustic transmitters is described. The present paper presents results from an extensive mapping of signal strengths and the proportion of correctly identified codes from a transmitter at various positions outside automatic listening stations (ALS). The system is evaluated on the basis of two field seasons, during which 107 Atlantic salmon, Salmo salar L., were tagged with acoustic transmitters in a fjord system in south-western Norway. By installing one ALS (two at high water discharges) in the mouth of the River Suldalslågen and two ALSs in the Hylsfjord, the presence and swimming direction of all tagged salmon entering the river and the inner part of the 750-m-wide Hylsfjord were recorded.     

浅谈猪的配套系

1 “配套系”简释 “配”者,对个体而言,有两性结合、配种之意;对群体而言,有分工、配合、互补之含意。“套”有套用、把缺少的东西补足之意,“配套”就是把若干相关的事物组合成一整套。“系”有品系、系列、体系、系统之意。“配套系”在此可理解为：在一个育种目标内的一组品系系列,在品系内部,根据生产性能的不同进行分工(父系、母系),其中一些品系选择性的专用于同另一些品系进行配套杂交,以期获得兼有双亲优点的具有显著杂种优势的杂种后代作为经济利用。     

淡水鱼类原良种场设施--水体自然净化系统的设计理念与建设实践

1 前言 20世纪80年代以来,我国建设了一批淡水鱼类的种质保存与繁育基地(即淡水鱼类原良种场).这对于保持淡水鱼类的遗传多样性状相对稳定,延缓退化和推广良种发挥了非常重要的作用,有力地推动了淡水渔业向前发展.     

在淡水鱼类混养系统中吊养三角帆蚌对养殖产量和水质的影响

通过78 d围隔养殖实验检验了在草鱼、鲫、鲢、鳙混养系统中吊养三角帆蚌对鱼产量和水质的影响。设2个处理,处理Ⅰ混养草鱼、鲫、鲢和鳙,处理Ⅱ在处理Ⅰ基础上按鱼∶蚌=1∶1的比例配养三角帆蚌。实验期间定期采样分析浮游植物种类组成和生物量、初级生产力(P)、群落呼吸(R)、溶氧(DO)、pH、透明度(SD)、主要离子(CO2-3、HCO-3、Cl-、SO2-4、Ca2+、Mg2+)、总碱度、总硬度、氨态氮、亚硝酸态氮、硝酸态氮、活性磷、总氮(TN)、总磷(TP)、总有机碳(TOC)、高锰酸钾指数(COD M n)和生化耗氧量(BOD5)。结果发现,吊养三角帆蚌显著降低水体中Ca2+浓度,但对其他指标均无显著影响。处理Ⅱ草鱼、鲫、鲢产量略高于处理Ⅰ,而鳙产量略低于后者,表明在草鱼、鲫、鲢、鳙混养系统中按1∶1的比例配养三角帆蚌不会导致草鱼和鲫产量下降,但导致鳙产量降低。处理Ⅱ浮游植物多样性(Shannon-Weaver多样性指数、Margalef丰富度指数、Pielou均匀度指数和种类数)、P、P/R、SD和DO略高于处理Ⅰ,而氨态氮、活性磷、TN、TP、COD M n、BOD5和TOC略低于后者,表明在混养系统中配养三角帆蚌可显著降低养殖水体Ca2+浓度,同时可在一定程度上提高浮游植物多样性、P和DO并降低TN、TP、COD M n、BOD5和TOC。结果表明,在淡水鱼类混养系统中适度配养三角帆蚌可提高养殖的经济效益,同时有助于降低养殖系统内氮、磷和有机废物的积累。     

Development of a label-free immunosensor system for detecting oocyte maturation-inducing hormone in fish

A label-free immunosensor for detecting the oocyte maturation-inducing hormone 17, 20β-dihydroxy-4-pregnen-3-one (DHP), was developed. A principle of the sensor system was based on differences in electrochemical activity changed by an immunoreaction in the absence and presence of DHP. For preparation of the immunosensor, anti-DHP IgG was immobilized on an Au working electrode modified with a self-assembled monolayer of 3-mercaptopropionic acid. The sensor was immersed into a sample solution containing DHP. DHP was determined by cyclic voltammetry. The immunosensor showed a specific response to DHP, and the oxidation peak current linearly decreased in the range of 7.8–500 pg ml⁻¹ with a correlation coefficient of 0.996. The sensor system was applied to determine the DHP levels in plasma of goldfish and was compared with the DHP levels of the same samples determined using an ELISA as the conventional method. Good correlation was obtained between values determined using both methods in the range of 0.1–7.7 ng ml⁻¹ (correlation coefficient 0.876). These findings suggest that the proposed label-free immunosensor can be used to analyze DHP levels in fish plasma samples.     

Development of a label-free immunosensor system for detecting plasma cortisol levels in fish

Fishes display a wide variation in their physiological responses to stress, which is clearly evident in the plasma corticosteroid changes, chiefly cortisol levels in fish. In the present study, we describe a novel label-free immunosensor for detecting plasma cortisol levels. The method is based on immunologic reactions and amperometric measurement using cyclic voltammetry. For the immobilization of the antibody on the surface of sensing electrode, we used a self-assembled monolayer of thiol-containing compounds. Using this electrode, we detect the CV signal change caused by the generation of antigen–antibody complex. The immunosensor showed a response to cortisol levels, and the anodic peak value linearly decreased with a correlation coefficient of 0.990 in diluted plasma. The specificity of the label-free immunosensor system was investigated using other steroid hormones, such as 17α, 20β-dihydroxy-4-pregnen-3-one, progesterone, estriol, estradiol, and testosterone. The specific detection of cortisol was suggested by a minimal change from ?0.32 to 0.51 μA in the anodic peak value of the other steroid hormones. The sensor system was used to determine the plasma cortisol levels in Nile tilapia (Oreochromis niloticus), and the results were compared with those of the same samples determined using the conventional method (ELISA). A good correlation was obtained between values determined using both methods (correlation coefficient 0.993). These findings suggest that the proposed label-free immunosensor could be useful for rapid and convenient analysis of cortisol levels in fish plasma samples.     

工厂化海水养鱼循环系统的工艺流程研究

讨论了一种经济型的封闭式海水养殖水处理技术。包括机械过滤固体废弃物、泡沫分离悬浮物、臭氧消毒、生物膜降解“三态氮”、滴滤除去气态废弃物、贝壳调节pH、氧气罩与溶氧罐混合氧浴增氧等工艺,并就研制的活性生物填料进行了净水实验。结果表明,经过以上系统处理后的水质指标为：COD＜2．8mg／L,SS＜7．2mg／L,非离子氨＜0．02mg／L,细菌含量低于自然海水,养殖牙鲆平均单产为29．92kg／m^2,成活率为95．39％。     

节能型半滑舌鳎循环水养殖车间优化设计

优化设计建设了半滑舌鳎循环水养殖车间,车间建筑面积2 880 m2,养殖水面1 340 m2.优化设计主要包括节能型养鱼车间、循环水处理工艺、补充水及外排废水处理工艺、养鱼池、生物滤池及渠道式紫外线消毒池设计.该养鱼车间比一般低拱车间节能30%以上.生物滤池为4段流水式结构.养鱼池能自动清污,倒U形管控制水位.渠道式紫外线消毒池消毒效率高,细菌去除率99%以上.通过养鱼工程优化设计及基地建设,提出了我国未来海水循环水养殖的三级推广模式.     

溢油事故对天然渔业资源损害的评估指标体系与实例应用

实验结合2006年4月发生在舟山沿岸渔场的韩国籍现代独立轮溢油事故案例,探讨了溢油事故对天然渔业资源损害的评估指标体系。研究结果提出了溢油事故对天然渔业资源损害的评估指标体系由溢油事故污染指标子体系和天然渔业资源损害评估子体系二大部分构成。其中溢油事故污染指标子体系主要包括溢油品种特征、溢油时间特征、溢油空间特征,溢油区域环境特征、溢油动态特征和采取的防范措施;天然渔业资源损害评估子体系主要包括污染前后天然渔业资源的种类、单位面积资源生物数量,各种资源生物的损害率、损失量、恢复措施和所需费用。同时提出溢油事故渔业损害的评估程序和在不同情形下,各指标参数的选取方法。案例研究结果得出该事故造成渔业受到严重影响的海域范围在100km2(≥5.0mg/L)以上,鱼卵和仔鱼的总损失量分别为6700万个和117000万尾,鱼、虾和蟹类幼体总损失量分别为3681、17045和406万尾,底栖动物总损失量为8162万个,事故海域渔业资源恢复直接所需总费用为1822万元。研究结果表明,建立的溢油事故对天然渔业资源损害的评估指标体系具有较强的可操作性,可为溢油事故对天然渔业资源损害索赔提供参考。     

Fish welfare assurance system: initial steps to set up an effective tool to safeguard and monitor farmed fish welfare at a company level

The objective was to take a first step in the development of a process-oriented quality assurance (QA) system for monitoring and safeguarding of fish welfare at a company level. A process-oriented approach is focused on preventing hazards and involves establishment of critical steps in a process that requires careful control. The seven principles of the Hazard Analysis Critical Control Points (HACCP) concept were used as a framework to establish the QA system. HACCP is an internationally agreed approach for management of food safety, which was adapted for the purpose of safeguarding and monitoring the welfare of farmed fish. As the main focus of this QA system is farmed fish welfare assurance at a company level, it was named Fish Welfare Assurance System (FWAS). In this paper we present the initial steps of setting up FWAS for on growing of sea bass (Dicentrarchus labrax), carp (Cyprinus carpio) and European eel (Anguilla anguilla). Four major hazards were selected, which were fish species dependent. Critical Control Points (CCPs) that need to be controlled to minimize or avoid the four hazards are presented. For FWAS, monitoring of CCPs at a farm level is essential. For monitoring purposes, Operational Welfare Indicators (OWIs) are needed to establish whether critical biotic, abiotic, managerial and environmental factors are controlled. For the OWIs we present critical limits/target values. A critical limit is the maximum or minimum value to which a factor must be controlled at a critical control point to prevent, eliminate or reduce a hazard to an acceptable level. For managerial factors target levels are more appropriate than critical limits. Regarding the international trade of farmed fish products, we propose that FWAS needs to be standardized in aquaculture chains. For this standardization a consensus on the concept of fish welfare, methods to assess welfare objectively and knowledge on the needs of farmed fish are required.