Drag force acting on biofouled net panels

Measurements were made to assess the increase in drag on aquaculture cage netting due to biofouling. Drag force was obtained by towing net panels, perpendicular to the incident flow, in experiments conducted in a tow tank and in the field. The net panels were fabricated from netting stretched within a 1 m² pipe frame. They were towed at various speeds, and drag force was measured using a bridle-pulley arrangement terminating in a load cell. The frame without netting was also drag tested so that net-only results could be obtained by subtracting out the frame contribution. Measurements of drag force and velocity were processed to yield drag coefficients.

Clean nets were drag tested in the University of New Hampshire (UNH) 36.5 m long tow tank. Nets were then exposed to biofouling during the summer of 2004 at the UNH open ocean aquaculture demonstration site 1.6 km south of the Isles of Shoals, New Hampshire, U.S.A. Nine net panels were recovered on 6 October 2004 and immediately drag tested at sea to minimize disturbing the fouling communities. The majority of the growth was skeleton shrimp (Caprella sp.) with some colonial hydroids (Tubularia sp.), blue mussels (Mytilus edulus) and rock borer clams (Hiatella actica). Since the deployment depth was 15 m (commensurate with submerged cages at the site), no algae were present. The net panels had been subject to several different antifouling treatments, so the extent of growth varied amongst the panels. Drag force measurements were made using a bridle-pulley-load cell configuration similar to that employed in the tow tank. Fixtures and instruments were mounted on an unpowered catamaran that was towed alongside a workboat. Thus, the catamaran served as the “carriage” for field measurements.

Increases in net-only drag coefficient varied from 6 to 240% of the clean net values. The maximum biofouled net drag coefficient was 0.599 based on net outline area. Biofouled drag coefficients generally increased with solidity (projected area of blockage divided by outline area) and volume of growth. There was, however, considerable scatter attributed in part to different mixes of species present.     

Response of offshore cultivated Laminaria saccharina to hydrodynamic forcing in the North Sea

The aim of the presented investigation was to test the sensibility of macroalgal aquaculture in offshore wind farms in the North Sea and to find arguments for the choice of appropriate sites among the planned wind farms. Based on experience with an offshore aquaculture farm of Laminaria saccharina conducted in 2002, we assessed the maximum hydrodynamic forces affecting farmed algae by applying the model software “WaveLoad”. Drag measured in a towing tank was considerably higher on algae with a more ruffled margin and wider blade collected from sheltered environments than on flat and narrow farmed Laminaria despite comparable blade areas. Drag varied according to frond size, current velocity and acceleration reaction. Dislodgement of laminarian holdfasts and the forces necessary to break the stipe depended on blade length and surface area. Neither did our measured nor our calculated values of drag exceed those forces, provided the algae had been grown in a current > 1 m s^− 1. Even in storm conditions with maximum current velocities of 1.52 m s^− 1 and wave heights of up to 6.4 m can cultivated L. saccharina withstand the high energy environment.     

桑沟湾养殖海带生长的模型预测

海带(Saccharinajaponica)是一种常见的大型经济褐藻,是海洋生态系统重要的初级生产者,也是我国北方沿海主要的养殖藻类。本研究旨在建立海带个体生长数值模型,并以此预测中国北方近海大规模筏式养殖条件下海带的生长情况。本研究以桑沟湾养殖海带为例,利用可视化模型软件STELLA描述海带生长的关键过程及其与环境参数的关系,以净生长量(N_(growth))=总生长量(G_(growth))–呼吸作用(resp)–枯烂(E_(kelp))为基本框架,模拟和预测海带的生物量和叶片长度变化。海带的总生长用光照、温度、盐度、海带体内营养盐(包括N和P)等强制函数定义,其中,光照参数来自桑沟湾气象记录,盐度、温度和营养盐为现场调查实测值。模型模拟桑沟湾养殖海带的长度与干重结果与实测值的拟合度R~2值分别为0.936、0.963,说明该模型能够很好反映海带的真实生长情况。可靠的个体生长模型是评估海带养殖容量的基础,并可为水产养殖区的空间规划提供决策依据。     

基于GIS的桑沟湾及周围海域海带养殖适宜性评价

目前水产养殖面临用海冲突、单位面积和人均生产率偏低、养殖业的生态和经济成本较高等问题。为充分利用海区的自然生产力,提高养殖效率和效益,需要对海区进行适宜性评价,选择最适宜的水域进行养殖。以桑沟湾及周围海域主要的养殖品种海带(Saccharina japonica)作为评价对象,选取光照、温度、流速、无机氮、盐度、深度作为适宜性评价指标,利用遥感技术确定海区养殖布局,通过野外调查和数据模拟获取养殖海区环境参数数据,根据动态能量学(Dynamic energy budget, DEB)模型——STELLA模型敏感性分析结果,并结合层次分析法计算评价指标权重,海带生长相关环境因子的强制函数拟合得到单因子评分曲线进行评分。最后,采用线性加权叠加分析方法得到海带养殖适宜性评价结果。适宜性评价过程以地理信息系统(Geographical information systems, GIS)作为技术支持,利用GIS空间插值功能生成光照、温度、流速、无机氮、盐度、深度专题图层,采用栅格计算功能对各专题图层进行叠加,得到综合多因素的海带养殖适宜性评分和适宜性等级。评价结果显示,在不考虑用海冲突的情况下,桑沟湾及周围海域海带养殖适宜性分数分布在0~6.7范围内,分值主要集中在4~6分,属于中等适宜,占研究区总面积的67%,最适宜和不适宜分别占研究区总面积的23%和10%,无一般适宜区。评分较高的区域主要分布在北部爱莲湾和楮岛东部海域周围,适宜性评分较低的区域主要位于近岸水深较浅的海域。根据适宜性评价结果可进行水域空间规划和安排养殖生产计划,为管理部门开展养殖分区和海洋功能区划提供参考。     

七带石斑鱼和云纹石斑鱼幼鱼在封闭循环水条件下的生长特性

观测研究了七带石斑鱼(Epinephelus septemfasciatus)幼鱼和云纹石斑鱼(Epinephelus moara)幼鱼在封闭式循环养殖系统中的生长特性,用SPSS 17.0软件中的Curve Estimation对相关数据进行模型分析与参数估计。结果表明,经过122 d的养殖,七带石斑鱼幼鱼平均体质量由(114.836±25.343)g增加到(213.861±38.604)g,相对增长率为0.707%,全长(TL)与养殖时间(t)的函数关系式为TL=-0.006t3+1.622t+13.954,体质量(W)与体长(BL)的关系式为W=0.436BL2.055;云纹石斑鱼幼鱼平均体质量由(79.620±13.007)g增加到(238.086±46.307)g,相对增长率为1.631%,全长(TL)与养殖时间(t)的函数关系式为TL=-0.013t2+2.008t+11.540,体质量(W)与体长(BL)的关系式为W=0.018BL3.083。两种幼鱼丰满度生长差异不显著(P0.05),都保持在2.2-3.4之间。     

Genetic comparison of wild and cultivated European populations of the gilthead sea bream (Sparus aurata)

This study represents the first large-scale population genetic analysis of the marine fish gilthead sea bream (Sparus aurata), one of the most significant species in the South European aquaculture. Six wild and five cultivated sample sets covering the South Atlantic and Mediterranean European area have been screened for allozyme, microsatellite and mitochondrial DNA (mtDNA) variation. Microsatellites showed higher levels of polymorphism than allozymes. The low variability of mtDNA offered no basis for population differentiation.

The results reveal levels of variability for S. aurata above those from other sparids. Cultivated populations show a slight decrease of variability related to the wild ones, but not sufficient to document inbreeding depression effects, thus suggesting a fairly proper management. Wild populations reveal a slight degree of differentiation more pronounced with microsatellites than with allozymes, but not apparently associated with geographic or oceanographic factors. The cultivated populations seem to be highly divergent as a result of genetic drift caused by different factors pertaining to their respective histories. With both markers, the two cultivated Spanish sample sets are the most divergent. The high differentiation between cultivated and wild populations from the same area might indicate no evidence for significant genetic flow between them.

This study provides an insight into the population structure of S. aurata, although more questions have arisen that need to be solved. This can be achieved by further screening of small-scaled targeted sample sets in the studied area.     

Testing the efficacy of bouncing-bucket nursery systems for enhancing shell strength and thickness in on-bottom cultured Eastern oysters (Crassostrea virginica)

Through physical manipulation, oyster growers can modify the morphological features of young oysters in order to improve their robustness and resiliency to predation. In this study, the efficacy of a novel passive culturing technique using floating buckets that “bounce” oysters prior to the benthic grow-out phase for enhancing shell thickness and strength, while not compromising oyster shape, was investigated. Using a field experiment, we quantified and compared the shell thickness (mm), compressive strength (Newtons), and shape (fan ratios and cup ratios) of juvenile oysters subjected to this bouncing technique with oysters grown in floating bags, the current industry standard. Results indicated that bouncing increased shell thickness and strength for oysters >45 mm shell height compared to control oysters, but also decreased shell thickness and strength for oysters <45 mm shell height compared to control oysters. There was no difference in shell shape between bounced and control oysters, with both groups having similar fan and cup ratios. Ultimately, our results suggest that the size at which bounced oysters are released to the benthos for grow out will dictate the usefulness of bouncing technique for reducing predation-related mortality.     

调味海带的食用加工及营养学评价

根据目前对功能食品的看好,研制出适合大众口味的方便即食调味海带,并分析了它们的主要营养成分及对微生物指标的检测,结果表明,调味海带中碘含量为0.026％,蛋白质含量为13.35％,脂肪为1.38％,粗纤维为9.5％,钙含量偏低,只有0.65％,灰分含量很低,仅为4.32％。微生物(包括细菌总数、大肠菌群和致病菌等)指标均符合国家食品卫生标准。因此研制出的调味海带是一种高蛋白、低脂肪、低热量、营养丰富的方便食品。     

平面网衣在水流作用下的受力和变形特性数值模拟研究

基于集中质量点法和牛顿第二定律,建立了网衣在水流作用下的受力和运动响应数学模型.采用计算机数值模拟方法,研究了水流作用下网衣的动态变形情况以及网衣受力平衡后的空间分布形状.在2种配重(GW1=4.12 N、GW2=16.38 N)和6种流速(U=0.17、0.22、0.28、0.33、0.39和0.44 m · s-1)条件下对网衣稳定后沿水流方向的总水流力、网衣底端的水平及垂直位移进行了数值计算.计算结果表明,配重及流速大小对网衣受力和变形特性具有较大的影响.随着水流速度的增大,网衣在水流作用下的运动变形加剧,且当配重增大时,网衣变形减小,网衣受力随流速的变化增幅明显加快.为了验证模型的正确性和有效性,文章还将数值模拟结果与前人的试验结果进行了比较,效果良好.     

转变增长方式是我国水产养殖持续发展的必由之路

水产养殖业是渔业中的重要产业之一,已经成为我国水产品市场供给的主要来源。在回顾我国水产养殖业取得伟大成就的同时,也认识到水产养殖业的发展面临着诸如水资源严重缺乏、耕地资源不断被压缩、水产养殖良种覆盖率水平不高、饲料原料短缺、劳动力不足、水产疫苗和药物发展滞后、质量安全和水产品品质安全等问题。认为唯有转变水产养殖的增长方式才是我国水产养殖持续发展的必由之路,如通过转变现有养殖模式,提高单位水体的产量;转变饲料投喂模式,普及高效环保饲料,开发替代鱼粉的新蛋白源;提高优良品种选育与普及水平;加强疫苗创制能力,扩大其应用范围;转变消费习惯,提升加工与流通领域发展水平等措施。水产养殖产品是我国乃至全世界经济社会可持续发展的刚性需求,政府应从战略高度认识到通过转变增长方式实现我国水产养殖业可持续发展的重要意义。     

Measuring technical,allocative and cost efficiencies of seabass and seabream farms in Greece

Abstract

A stochastic Cobb‐Douglas production frontier is used to provide estimates of output‐oriented technical efficiency, input‐oriented technical efficiency, input allocative efficiency and cost efficiency for a sample of seabass and seabream farms in Greece. Mean output‐oriented technical efficiency is estimated at 78.5%, input‐oriented technical efficiency at 73.6%, input allocative efficiency at 79.2%, and cost efficiency at 58.2%. Considering the sources of efficiency differentials among fish farms, it is evidence from the empirical results that large farms tend to achieve higher (technical and allocative) efficiency scores; specialization in either seabass or seabream affects positively technical and cost, but not allocative, efficiency; and utilization of skilled labor seems to have a positive impact only on technical efficiency.     

铁离子对海带配子体克隆系生长发育的影响

为了探究Fe³⁺在不同氮、磷条件下对海带（）配子体生长发育的影响,以海带''黄官1号''雌、雄配子体克隆系为材料,以含有不同浓度的氮（N）、磷（P）营养盐的灭菌海水为培养液,添加不同浓度（0μmol/L、0.36 μmol/L、3.60 μmol/L、8.90 μmol/L、17.80 μmol/L）的铁离子（Fe³⁺）,通过测定光系统Ⅱ的最大荧光产量（）观察配子体营养生长状况,通过计算发育率（包括卵囊形成率、排卵率、幼苗形成率）观测配子体发育与生殖状况。结果显示,N、P浓度分别为0.825 mmol/L、0.0336 mmol/L的条件下,浓度为3.60 μmol/L的Fe³⁺对海带配子体营养生长阶段的促进作用最大;在不同N、P浓度条件下,Fe³⁺浓度为3.60~17.80 μmol/L时能够提高海带配子体的最大荧光产量,且各浓度组之间没有显著性差异（3+能够促进海带配子体由营养生长转向生殖生长,Fe³⁺浓度为3.60~17.80 μmol/L时可显著促进海带配子体的生殖生长,且各浓度组之间没有显著性差异（>0.05）;即使N、P浓度达到0.825 mmol/L、0.0336 mmol/L,在无铁条件下所有的海带配子体维持在营养生长状态;即使Fe³⁺浓度达到3.60 μmol/L,在N、P浓度0.007 mmol/L、0.0003 mmol/L条件下,大部分海带配子体（65%）维持在营养生长状态,虽然小部分海带配子体（35%）进入了生殖生长状态,但生殖生长明显滞后于实验中的其他各个N、P浓度组。本研究表明,铁和N、P营养盐对海带配子体的营养生长和生殖生长具有协同促进作用,铁是海带配子体由营养生长到发育成熟再到有性生殖过程中的关键因素;在添加适宜浓度的氮（0.275 mmol/L）、磷营养盐（0.0112 mmol/L）条件下,浓度为3.60 μmol/L的Fe³⁺对海带配子体的生长发育促进作用最大。该结果可为提高海带育苗效率提供理论依据。     

Research on the jellyfish (<Emphasis Type="Italic">Rhopilema esculentum</Emphasis> Kishinouye) and associated aquaculture techniques in China: current status

The jellyfish is a popular seafood in eastern and southern Asian nations where there is a high market demand that stimulates large-scale jellyfish production. Due to its economic importance in China, many biological studies have focused on the jellyfish Rhopilema esculentum Kishinouye in terms of the environmental impact of aquaculture activities and culture techniques. In recent years, the commercial aquaculture of R. esculentum has expanded greatly in China. This paper summarizes the current status of research in China on R. esculentum and associated aquacultural practices, focusing on a number of related technological approaches.     

浅海围栏牧场中柱桩受力及波浪场分布试验

通过物理模型试验的方法,对浅海围栏牧场设施中柱桩的受力及内部波浪场进行了研究。试验模型整体采用1∶20比尺,试验波要素设定五个波高,原型分别为1、2、2.5、3、3.5m,五个波浪周期分别为5、6、7、8、9s,五个流速分别为0.5、0.76、1、1.25、1.57m/s。测量在不同波流组合以及不规则波单独作用和流单独作用下迎浪侧最前方单根桩柱的受力情况及围栏牧场内波浪场情况。试验结果显示,随着波高和流速的增加,桩柱所受到的波流力逐步增大,在计算柱桩受力时,需要考虑到网衣受力带来的影响。波高及周期越大,围栏设施内的波浪场分布规律越明显,沿着波浪传播方向呈逐渐减小趋势,小波高及短周期时波浪场分布规律不明显。     

HDPE圆柱形网箱与圆台形网箱受力变形特性的比较

介绍了一种用于模拟水流作用下网箱受力变形的数值计算模型,并利用海上实测数据对计算模型进行了验证。验证结果表明,网箱锚绳力的计算结果与实测数据十分接近,最大相对误差为7.0%。在此基础上,分别对圆柱形网箱和圆台形网箱在不同配重(GW₁=350 kg、GW₂=600 kg)和流速(U=0.3～0.9 m/s)条件下所受的水流力以及容积损失率进行了数值计算。结果表明,两种网箱无论在所受的水流力方面还是在变形后保持的网箱容积方面随流速和配重的变化趋势基本一致。圆柱形网箱的容积损失率远大于圆台形网箱的容积损失率,在较小流速(U=0.3 m/s)研究时,圆柱形网箱的容积损失率达到了28%左右,具有较明显的初始变形。圆台形网箱的初始变形很小,具有较好的耐流特性和抗变形能力。     

Growth and biomass production of Tetraselmis suecica and Dunaliella tertiolecta in a standard medium added with three products of zeolitic nature

At the end of the exponential growth phase, the cell concentrations of batch cultures of Tetraselmis suecica and Dunaliella tertiolecta grown in f medium added with 5, 10 and 20 mg l⁻¹ of the zeolitic products Zestec 56, Zesep 56 and Zeben 06 (ZT56, ZS56 and ZB06) were similar to those obtained with the same medium without zeolites. At the end of the following period of slow growth, all the experimental media gave significantly higher concentrations of T. suecica than the control cultures, but only the addition of 20 mg l⁻¹ of ZT56 and ZB06 gave significantly better results with D. tertiolecta. However, in all cases the final harvests of total and ash-free biomass were similar to those of the controls, indicating the presence of smaller or lighter cell in the experimental cultures. The effect of these products is to enhance cell division rates in the phase of slow growth, with no advantage in terms of biomass production.     

海水养殖对近岸生态环境的影响

文章研究了从硝化菌群中分离的菌株NB5在不同培养条件下的生长情况及其对氨氮 (NH₄ ⁺-N) 和亚硝氮 (NO₂ ⁻-N) 的去除效果,并对菌株NB5进行了鉴定。结果发现,菌株NB5在盐度25~45、pH 6.0~9.0、15~35 ℃和通气量1~2 L·min⁻¹的条件下生长良好 (P>0.05)。在盐度45、35和25条件下对NH₄ ⁺-N的最大去除率分别为96.24%、88.93%和75.08%;pH 7.5和9.0条件下分别为99.53%和99.37%;温度30、25、15和35 ℃条件下分别为99.53%、97.22%、97.29%和71.26%;通气量为2和1 L·min⁻¹时分别为99.87%和99.82%。在上述培养条件下菌株NB5对NH₄ ⁺-N的最大去除率均显著高于对照组和其他条件组 (P<0.05)。菌株NB5在不同培养条件下对NO₂ ⁻-N浓度变化无显著作用 (P>0.05)。经16S rDNA序列分析,菌株NB5鉴定为海水硝酸盐还原菌 (Nitratireductor aquimarinus)。研究表明,菌株NB5具有较好的环境适应性和氨氮去除效果,尤其适合中高盐度 (25~45) 养殖池塘环境。

     

Bacterial community structure and activity in fish farm sediments of the Ligurian sea (Western Mediterranean)

The environmental impact of a well-established fish farm has beeninvestigated in surface sediments of the Ligurian Sea in order to assess thebiodeposition, bacterial community structure and dynamics at a mature stage oforganic enrichment.The Biopolymeric carbon (BPC) fraction of organic matter and phytopigmentconcentrations displayed very high values beneath the fish cages. In particularlipid, carbohydrate and chlorophyll-a concentrations werehigher in farm sediment while protein concentrations did not show significantchange between farm sediment and control.Benthic bacteria were closely related to organic enrichment and their densitywas three times higher (up to 3 × 10¹⁰ cellsg^–1) in stations beneath the cages being positivelycorrelated with BPC (n = 10, p < 0.05) and lipid (n = 10, p < 0.05)concentrations. Colony forming units (CFU) counts of heterotrophic bacteriaindicate a shift in the relative importance of the gram negative bacterialfraction, displaying the predominance of theCytophaga/Flexibacter-like bacteria (CBF), as well as theoccurrence of pathogenic bacteria (such as Vibrio) insediments beneath the farm. In contrast, Gram positive bacteria were moreprevalent in control site where they represented up to 90% of total isolates.Aminopeptidase activity displayed higher values in sediment beneath the cages,whereas the enzymatic activity per bacterial cell was lower. These data suggesta functional stress of bacterial degradation rates and represent a potentialvaluable environmental index of imbalance between supply and removal of organicmatter in eutrophicated environments.Data presented in this study also suggest that either the biochemicalcomposition of sedimentary organic matter as well as the selected microbialvariables may represent useful tools for evaluating the effects of organicenrichment due to fish farming and could be proposed as new environmentalindices of aquaculture impact on marine sediment.     

Effect of pressure and pH in ammonium retention for nanofiltration and reverse osmosis membranes to be used in recirculation aquaculture systems (RAS)

Recirculation systems are becoming widely used in the aquaculture industry, where ammonium removal results are crucial for a proper performance considering its high toxicity on fish. The objective of this study was to assess the ammonium retention, when the transmembrane pressure (TMP) in nanofiltration (NF) and reverse osmosis (RO) membranes are changed. Two pH levels were tested: pH 5, where ammonium is as NH⁴⁺, and pH 7 which is an average of the most common range in aquaculture (pH 6-8). In this study a model solution of ammonium-water and commercial membranes of polyamide supplied by Alfa Laval (DSSHR98PP) and Dow (NF90, NF200 and NF270) were used, with a membrane area of 0.01018 m². A critical TMP was determined, where the repulsive electrochemical forces at the active layer were exceeded by the transmembrane pressure, causing an irreversible decrease of the retention values. The maximum TMP values for NF and RO membranes were 16 bar and 24.5 bar, respectively. Ammonium retention at pH 7 was higher than pH 5 for all assessed membranes before the critical TMP was reached, with average values of 100, 99.7, 98.4 and 87.5% for membranes NF90, DSSHR98PP, NF200 and NF270, respectively. It may be concluded the ammonium retention mechanism in the studied membranes basically corresponds to an electrochemical mechanism, where pH and critical TMP influence the retention values of ammonium.     

Formaldehyde degradation in denitrifying woodchip bioreactors: Effects of temperature,concentration and hydraulic retention time

Formalin is applied in certain aquaculture systems to control parasites infestations as well as bacterial and fungal diseases. This study investigated the capacity of end-of-pipe denitrifying woodchip bioreactors to remove potentially harmful amounts of residual formaldehyde (FA) from aquaculture effluents. Formaldehyde was readily removed by experimental- and field-scale denitrifying woodchip bioreactors and the removal of FA was found to be a combination of an initial adsorption of FA to woodchip surfaces (52 ± 2.8 g FA/m³ woodchips) and microbial degradation. Volumetric FA removal rates reaching 261 ± 27 g FA/m³/d were found at FA inlet concentrations of 90 mg FA/L and hydraulic retention times (HRT) of 5 h. High FA removal efficiencies ranged from 88.3 ± 4.6–99.8 ± 0.2% found for FA inlet concentrations –up to 105 mg FA/L and HRTs between 3.4 and 15 h. Microbial FA degradation rates in woodchip bioreactors were positively correlated to temperature with a Q₁₀ value of 2.27 and a corresponding Arrhenius temperature coefficient of 1.086 for the investigated temperature range of 7–23 °C. At a commercial, outdoor recirculating aquaculture system (RAS) three full-scale woodchip compartments, achieved an average volumetric FA removal rate of 29.4 ± 0.2 g FA/m³/d and a removal efficiency of 82.5 ± 0.8% during the first 24 h following addition of FA. The results demonstrated that woodchip bioreactors are efficient in removing residual FA from RAS effluents and that nitrate removal was transiently enhanced during FA removal.