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.  

铜合金网衣在海水养殖中的应用研究进展

铜合金网衣在渔业工程领域特别是网箱和围栏网海水养殖中得到了广泛的应用,并取得良好效果.铜合金网衣具有“0”生物附着、高效低碳、健康环保等特点.本文结合国内外在海洋、环境和金属材料等领域对铜合金研究已取得的成果,探讨了铜合金网衣在海洋中的抗污、耐腐蚀机理;通过介绍几种铜合金网衣类型,描述了两种结构类型的铜合金网衣网箱的制作方法以及在网箱养殖应用中常见的问题,并分析了其结构、力学特性和抗风浪能力等作业性能的关系,对铜合金网衣网箱在渔业上的应用情况及研究进展进行了梳理,以期为铜合金网衣网箱的进一步研究和应用提供参考.  

Formation of periphyton biofilm and subsequent biofouling on different substrates in nutrient enriched brackishwater shrimp ponds

Periphyton grown on substrates is known to improve water quality in aquaculture ponds. Five different substrates, (i) bamboo pipe (ii) plastic sheet (iii) polyvinylchloride (PVC) pipe (iv) fibrous scrubber, and, (v) ceramic tile were evaluated for the formation of biofilm in this experiment. The substrates were suspended 25 cm below the water surface. Each type of substrate was collected fortnightly to analyze the abundance and biomass of different periphytic algae and of the biofouling organism. The study was terminated after 60 days due to severe fouling by polychaete. Results showed that pond water nutrients were high on day 60 with mean total ammonia-N, nitrite-N and soluble reactive phosphorus concentrations of 309.6 ± 8.6 μg L^− 1, 26.0 ± 2.7 μg L^− 1 and 87.2 ± 7.1 μg L^− 1 respectively. During the first two weeks the substrates were colonized by 19 periphytic algae. The most abundant family was Bacillariophyta (8 genera) followed by Chlorophyta (7 genera) and Cyanophyta (4 genera). Periphyton colonization on bamboo pipe showed the highest (p < 0.05) biomass in terms of chlorophyll a amongst all the substrates used. The biomass varied from 179 to 1137 μg m^− 2 with mean values of 1137.2 ± 0.6, 929.6 ± 0.6, 684.2 ± 1.2, 179.1 ± 0.6 and 657.0 ± 0.6 μg m^− 2 on bamboo pipe, PVC pipe, plastic sheet, fibrous scrubber and ceramic tile respectively for the first 15 days. From 3rd week, polychaetes began to form tubes on the substrate. By day 60, the whole surface of all substrates was covered with tightly packed polychaete tubes with mean densities of 168.0 ± 15.4, 121.0 ± 13.5, 72.8 ± 9.8, 72.4 ± 7.4 and 56.0 ± 6.8 polychaete tubes cm^− 2 for bamboo, PVC, plastic, fibrous scrubber and ceramic tile respectively. This study illustrated the invasive nature of attached polychaete thus hampering the formation of periphyton biofilm on substrates which could have been used for improving water quality in enriched brackishwater shrimp ponds.  

海水贝类养殖中污损生物的防除研究进展

据2002年统计，我国贝类养殖产量占海水养殖总量的79．4％，贝类养殖面积占海水养殖面积的66．9％，贝类养殖种类已发展到了30余种，其中主要为贻贝、扇贝、蛤、蚶、牡蛎等。贝类养殖已成为我国海水养殖业的重要组成部分。目前广泛采用的贝类养殖方式是网笼养殖，但是贝类在笼内放养一定时间后，一些海生动物、植物和微生物会在贝壳表面和养殖网笼的表面附着从而影响养殖贝类的正常生长。污损生物的大量出现严重影响了贝类养殖业的生产效率。如何有效地防止和减少污损生物对养殖贝类和养殖器具的危害，已成为水产养殖业的重要研究课题之一。  

Biofouling as a reservoir of <i>Neoparamoeba</i> <i>pemaquidensis</i> (Page, 1970), the causative agent of amoebic gill disease in Atlantic salmon

Amoebic gill disease (AGD) is currently the most important disease affecting the Tasmanian salmonid industry and is caused by a marine amoeba, Neoparameoba pemaquidensis (Page, 1970). In this study biofouling communities on salmon cages were surveyed for the presence of the disease agent over a period of 4 months. Malt–yeast–seawater (MYS) agar plates were used to culture N. pemaquidensis with its presence confirmed by immunofluorescent antibody test (IFAT). Positive percentages of categorised samples ranged from 0% to 55%. The survey detected the presence of N. pemaquidensis on a number of macrofouling species (in particular bryozoan Scrupocellaria bertholetti and solitary ascidian Ciona intestinalis), and in microfouling and water samples. High percentages of positive IFATs occurred in microfouling aggregates, the solitary ascidian, C. intestinalis, and centrifuged water samples. No positive IFATs occurred from samples of Caprella sp. The presence of N. pemaquidensis was sporadic and varied in species and over sampling month. Experimental exposure of Atlantic salmon, Salmo salar, to lightly fouled netting was conducted to assess the potential for microfouling to act as a source of infection. No signs of the disease were detected in fish exposed to lightly fouled netting treatments, while 100% of positive control fish were infected and had an average of 4.24±1.79 amoebae per field of view in IFAT of mucus smears. When combined with N. pemaquidensis loads in the water column, the loads of amoebae in biofouling communities may contribute to disease outbreaks. Thus, biofouling should be considered a risk factor for AGD outbreaks.  

桑沟湾筏式养殖鼠尾藻(Sargassum thunbergii)的生长特性

2014年4-6月在桑沟湾海区进行鼠尾藻(Sargassum thunbergii)海上筏式养殖实验,分析了鼠尾藻在桑沟湾的生长特性,调查了藻体上的附着生物.结果显示,(1)鼠尾藻在桑沟湾海域生长迅速,水温为10-17℃时特定生长率最高,可达6.10％/d;根据特定生长率与水温的关系,获得了鼠尾藻的最佳生长温度为14.9℃;(2)5月10日开始有生殖托形成,水温达到20.4℃时,鼠尾藻生殖托大量成熟,并有放散;(3)养殖期间,鼠尾藻最大长度达187.05 cm,均长可达112.31 cm;干湿比由0.147(4月)上升至0.189(6月);每公顷产量可达43.95 t(湿重),相当于干重为8.25 t;(4)藻体上有大型附着生物16种,主要优势种为尖嘴扁颌针鱼鱼卵、玻璃海鞘和海绵;附着生物的生物量随着水温升高而增加.研究表明,海区的附着生物对鼠尾藻的生长影响不大,在桑沟湾大规模养殖鼠尾藻是可行的.  

桑沟湾夏季栉孔扇贝养殖笼内水质变化

以2006年桑沟湾筏式养殖的栉孔扇贝为研究对象,测定了网笼内的水质状况及栉孔扇贝的死亡率,探讨了污损生物的可能影响.结果表明,(1)经过7个月的养殖,初始密度低于30个/层的实验组,栉孔扇贝的死亡率低于6%;高密度实验组(40个/层)的死亡率高达27%;(2)网笼内、外的磷酸盐、硅酸盐浓度没有显著性差异,但是,7、8月份的氨氮浓度差异较为明显;(3)同营养盐浓度的变化相比,网笼内、外叶绿素a浓度的变化较大,在9月份,高密度组的网笼内叶绿素a浓度低于0.67 mg/m3,食物可能为高密度组扇贝生长、存活的限制因子;(4)8月份,高密度组网笼内的细菌总数显著高于笼外及其他密度组.分析认为,高温期网笼内的水质状况及食物限制可能与养殖栉孔扇贝的死亡有关.  

Quantitative quality evaluation of Eastern oyster (Crassostrea virginica) cultured by two different methods

In order to evaluate the quality of oysters and whether a production method affects quality or not, a set of objective quantitative quality measures was developed. Eastern oysters (Crassostrea virginica) were cultured using two different treatments (never desiccated or desiccated daily with tidal exposure) and the meats were tested by textural, physico‐chemical and chemical analyses over a 25‐day cold storage period. Texture analyses parameters (cutting force and chewiness on oyster adductor muscles) were strongly correlated with storage time before the death of oysters and could be used as a quality indicator for oyster. Total volatile basic nitrogen (TVBN) could be used as freshness indicator for raw Eastern oysters, with the acceptability of 11 mg/100 g. Models for evaluating the quality of oysters were established that reflect the impact of a biofouling treatment on oyster's shelf life and texture attributes. The methods and quality indicators developed in this study were effective in evaluating the quality and freshness of Eastern oysters objectively, and could serve as routine quality check of oyster meat for the industry.  

PCR survey for Paramoeba perurans in fauna,environmental samples and fish associated with marine farming sites for Atlantic salmon (Salmo salar L.)

Amoebic gill disease (AGD) caused by the amoeba Paramoeba perurans is an increasing problem in Atlantic salmon aquaculture. In the present PCR survey, the focus was to identify reservoir species or environmental samples where P. perurans could be present throughout the year, regardless of the infection status in farmed Atlantic salmon. A total of 1200 samples were collected at or in the proximity to farming sites with AGD, or with history of AGD, and analysed for the presence of P. perurans. No results supported biofouling organisms, salmon lice, biofilm or sediment to maintain P. perurans. However, during clinical AGD in Atlantic salmon, the amoeba were detected in several samples, including water, biofilm, plankton, several filter feeders and wild fish. It is likely that some of these samples were positive as a result of the continuous exposure through water. Positive wild fish may contribute to the spread of P. perurans. Cleaner fish tested positive for P. perurans when salmon tested negative, indicating that they may withhold the amoeba longer than salmon. The results demonstrate the high infection pressure produced from an AGD‐afflicted Atlantic salmon population and thus the importance of early intervention to reduce infection pressure and horizontal spread of P. perurans within farms.