Effects of stocking density on survival,growth and biochemical composition of cultured mussels (Mytilus galloprovincialis,Lamarck 1819) from an offshore submerged longline system

This study examined an offshore submerged mussel longline system, in the Black Sea, from May 2009 to May 2010. The system was allowed 1 year for spat collection. After a 1‐year spat collection period, some spat collectors were left untouched (NS), and some spat collectors were grazed and socked (S) for a grow‐out study in May 2009. The effects of stocking density on the growth and survival of the S and NS mussels were examined. The biochemical composition of the mussels was also determined. Environmental factors including temperature, salinity, chlorophyll a, total suspended matter, inorganic matter and organic matter were monitored monthly during the experimental period. In May 2010, the mean length and live weight of the S and NS mussels were 60.46 ± 0.60 mm and 53.34 ± 0.37 mm, respectively, and 20.50 ± 0.50 g and 13.11 ± 0.26 g respectively. Mean moisture and ash were 82.35 ± 0.47% and 6.67 ± 0.44% respectively. Mean carbohydrate, protein and lipid were 27.74 ± 2.40%, 57.68 ± 2.15% and 7.91 ± 0.68% respectively. These results indicate that a submerged offshore mussel culture system in the Black Sea can be commercially convenient. In addition, stock management via thinning out of the spat can considerably increase the marketable size of mussels, reduce harvest time and produce better growth.     

Effect of water velocity on growth and retention of cultured Greenshell™ mussel spat, <Emphasis Type="Italic">Perna canaliculus</Emphasis> (Gmelin, 1791)

The Greenshell^TM mussel, Perna canaliculus, is a commercially important species forming New Zealand’s largest aquaculture export product. Losses of P. canaliculus spat from culture ropes between larval settlement and the time mussels reach initial reseeding size (c. 10 mm) are common. To test whether water velocity affects growth and retention of post-settlement P. canaliculus spat, and whether there is a threshold effect of increasing velocities on spat migration, a laboratory-based experiment was conducted. Spat were grown for 8 weeks in experimental tanks on culture ropes at four velocities typical of velocities within mussel farms (40, 10, 4, and 1 cm s⁻¹). Spat migration was observed at all the velocities tested, but the number of spat migrating decreased as water velocity increased. Spat retention was highest at the 40 cm s⁻¹ velocity. Mean spat size increased significantly with increasing water velocity. At the highest velocity tested (40 cm s⁻¹), migration increased as the spat grew suggesting that migration was density-driven. The results of this experiment indicate the potential for mussel farmers to reduce seeded spat loss and to increase the growth rate of spat by modification of the water flow within their farms, or placement of seeded ropes in locations of certain existing water velocities, and indicate that velocities in the range 15–40 cm s⁻¹ promote higher spat growth and spat retention for P. canaliculus.     

海州湾不同养殖区紫贻贝的营养特征及其影响因素

为探究海州湾不同养殖区紫贻贝(Mytilusgalloprovincialis)收获期营养成分变化及其影响因素,于2021年1—3月测定了海州湾不同养殖区(H1：离岸1 n mile,H2：离岸3 n mile,H3：离岸7 n mile、H4：离岸13 n mile,H5：离岸21 n mile)水环境理化因子、紫贻贝的条件指数及蛋白质、脂肪、糖原、氨基酸等营养成分,分析了水体理化因子与条件指数和营养成分的关系。结果显示,随着离岸距离的增加,水温和叶绿素a(Chl-a)浓度等关键理化因子均有升高趋势,1—3月H1站位紫贻贝的条件指数逐渐增加,H2～H5站位的条件指数均在2月达到峰值;各站位的紫贻贝总糖含量呈正态分布,于2月达到峰值,其中,H4和H5站位总糖含量在3月显著下降(P<0.05),比2月分别降低了62.7%和61.6%;H5站位紫贻贝的氨基酸含量在1月显著高于其他站位(P<0.05),而后,在3月显著降为各站位中最低(P<0.05);1—3月各站位紫贻贝外套膜的糖原含量呈先上升后下降的趋势,而3月H5站位紫贻贝糖原含量显著高于其他站位。本研究表明,紫贻贝营...     

Health and growth performance of the blue mussel (Mytilus edulis L.) from two hanging cultivation sites in the German Bight: a nearshore—offshore comparison

The health of cultivated blue mussels from an offshore and a nearshore sites was compared by assessing lysosomal membrane stability (LMS) and accumulations of lipofuscin and neutral lipids in the digestive glands. In addition, the condition index, parasite infestation rates, growth performance and energy status of the mussels were assessed during 10?months of sampling. Abiotic and biotic site characteristics were investigated by water analysis for each sampling cycle. Further, data of contaminant loads of the softbody and pollutant concentration of the water column, suspended particles and sediments from both sites were analysed. Results show that positive offshore effects due to dilution of contamination were not evident for all parameters analysed. Condition indices were high, and parasites were not present in offshore mussels. In contrast, the integrative health parameter LMS and growth performance were slightly, but not significantly, better in the nearshore cultivated mussels. These findings correspond with the higher contaminant concentrations in the softbodies of mussels and the water column from the offshore testing site. Both sites showed low LMS values and high accumulations of lipofuscin and neutral lipids, indicating that environmental conditions in the German Bight are generating stress for blue mussels even in the offshore areas. Exposure to fluvial transport points to a comparable probability for high contamination loads similar to nearshore areas. We therefore recommend adding a minimum salinity threshold to the definition of offshore aquaculture to exclude areas under fluvial influence.     

Protective socking material for cultivated mussels: a potential non-disruptive deterrent to reduce losses to diving ducks

Predation of cultivated mussels by diving ducks can threaten the viability of mussel farms. Conventional scaring tactics have had limited success at deterring ducks from feeding on cultivated mussels, because of rapid habituation and 24-h feeding cycles of some waterfowl species. We tested a socking material containing a biodegradable protective layer against predation by diving ducks on experimental blue mussel (Mytilus edulis) aquaculture sites in Prince Edward Island, Canada. We also assessed the effect of this new socking material on mussel growth and survival. Results showed that the protective socking has the potential to reduce losses to ducks, but did not perform well for all mussel seed sizes used by the industry. The protective layer also did not biodegrade fast enough, trapping a portion of mussels inside the sock, affecting growth and survival of these mussels. Improvements are needed to make this solution effective for all mussel sizes used by the industry and to make its production more cost effective.     

The feasibility of offshore aquaculture and its potential for multi-use in the North Sea

Following the Blue Growth ambition of the European Commission, the interest in the potential of offshore is growing. This paper aimed to contribute to the discussion on the feasibility of offshore aquaculture development and its potential for multi-use with other maritime activities. A review of national and international projects forms the basis of the paper, where the Dutch North Sea is used as a case-study area. Analysis of technical, economic and ecological boundaries indicated that the potential of fish culture is limited, that seaweed cultivation is likely to gain potential when challenges related to processing will be overcome and that mussel culture has the highest potential in the near future. The North Sea is an area where many stakeholders claim space, which might set boundaries to the number of sites available for mussel culture. Competing claims are a potential source of conflict but may also lead to mutual benefits when smart combinations are sought, e.g. with wind parks, fisheries and nature conservation; especially, the possibility of combining mussel culture in or around wind parks is worthwhile to be further explored. A spatial distribution model adapted for the Dutch North Sea conditions demonstrated that offshore mussel production in wind farms can be profitable. Yet, the commercial interest for offshore development of mussel culture is still limited. Actions required to stimulate further development of the offshore mussel industry are presented for the government, the private sector, research institutes and civil society organizations.     

The Effect of Frying – the Chemical,Microbiological, and Acrylamide Composition of Mussels as a Street Food

The effects of frying methods and covering processes on the proximate composition, fatty acid profile, amino acid profile, cholesterol, acrylamide, and microbiological content of fried mussel (Mytilus galloprovincialis 1819) were investigated in the present study. The group of mussels that were purchased for study was divided into six groups (control – unprocessed mussel meat; Group A – covered mussels fried in deep fat; Group B – mussel fried in low fat; Group C – uncoated mussel meat fried in deep fat; Group D – uncoated mussel fried in low fat; and Group E – mussel served in restaurants). It was determined that the mussel frying methods can affect the nutritional composition and cause changes in the amino acid, fatty acid, and cholesterol content.     

Evaluation of methods for assessing the retention of seed mussels (Perna canaliculus) prior to seeding for grow-out

The process of catching and relaying wild seed green-lipped mussels, Perna canaliculus, onto grow-out farms in New Zealand is extremely inefficient with the majority of the seed mussels being lost after transfer, mostly due to secondary settlement behaviour of the seed. In an attempt to identify the causes of this behaviour the retention of seed mussels was experimentally determined after exposure to three sub-lethal stressors, desiccation, starvation, and temperature fluctuation. In addition, two types of mussel seed behaviour were tested for their potential for developing a commercially useful method for identifying seed mussels with high retention properties prior to seeding. The two behaviours were the ability of seed mussels to attach by byssus threads to the substrate in slow flowing water, and the ability of seed mussels to pedal walk vertically up through a substrate filled column. Of the three stressors tested only desiccation and starvation significantly reduced mussel seed retention compared to “unstressed” controls by 38% (P < 0.05) and 42% (P < 0.05) respectively. Of the two types of mussel seed behaviour used for attempting to sort seed mussels, only the ability of seed mussels to attach by byssus threads to the substrate in slow flowing water showed any sensitivity for identifying individuals with higher retention properties (P < 0.05). Seed mussels that failed to byssal attach had a 23% lower mean retention, after 10 d experimental grow-out compared to seed that successfully attached. Although significant, this difference was relatively small and is unlikely to provide the basis for the development of a useful commercial seed mussel sorting method. Desiccation and starvation are both stressors that seed mussels are likely to experience during their commercial harvesting, transportation and seeding process. Consequently, seed mussels need to be relayed quickly and under moist conditions to reduce the potential for starvation and desiccation stress. Identifying seed mussels in poor nutritional condition and feeding them prior to seeding out on farms could also help to prevent the intermittent large scale seed mussel losses currently experienced. The application of these findings will assist in making more efficient use of the wild seed mussel resource and significantly lower financial losses to growers in New Zealand.     

Productive performance of brown mussels Perna perna (Linnaeus, 1758) cultivated on ropes at low densities in Caraguatatuba,Brazil

In Brazil, mussel seed are not a plentiful natural resource, and so the efficient use of seeds by reducing stocking densities should be considered. There are very few studies addressing the relationship between seeding density and growth of mussels in tropical conditions. This work aimed to determine the influence of low seeding densities on the productive performance of Perna perna (Linnaeus) mussels cultivated on ropes in Caraguatatuba, Brazil. In October 2014, 12 ropes, one metre in length each, were seeded at the densities of 200, 300 and 400 mussels/m (four ropes for each density) and suspended on a long line. After 226 days of growing, mussels were harvested and their performance at each density was evaluated in terms of mean weight and length, production, culture efficiency, condition index, survival, amount of recruited seed, amount of fouling on the ropes and morphometric relationships. We observed no significant differences (p > .05) for these indicators among the densities tested, except for mussel biomass, which was significantly higher (p < .05) at the greater densities. A partial budget analysis showed that the density of 400 m^?1 showed better profitability and should be recommended, even in case of seed shortage.     

The impact of the adult blue mussel (Mytilus edulis) population on settling of conspecific larvae

The choice of a mussel bed as a settling locality by conspecific mussel larvae is a trade-off between reduced fitness due to an increased risk of larval predation and post-settling food competition with the filtering adults and the benefit from a reduced post-settling mortality. This reduced post-settling mortality may be due to a reduced benthic predation in habitats with high complexity. In a field experiment, the larval settling of blue mussels, Mytilus edulis, was recorded on an artificial substrate 0.25, 1 and 2 m above the bottom during six periods in spring 1999. The experiment was conducted at four stations with dense mussel beds located at two of these stations. Two of the four stations, one with mussel beds and one without, were located in a wind-exposed area and the two other stations in a sheltered area. It was demonstrated that the larval settling was reduced up to 1 m above the mussel beds. A size analysis of the settled mussels indicated that the reduction in settling intensity close to mussel beds was due to a pre-settling process: the larvae were predated by the filtering adult mussels. Settling was significantly affected by wind stress. During periods with a high mean wind velocity and a turbulent water column, the larvae showed a reduced settlement 1 m above a mussel bed relative to 2 m above, whereas the same patterns not could be observed outside a mussel bed. The importance of the filtration activity of the adult mussels and the behaviour of the larvae is discussed. The recruitment of blue mussels into a mussel bed was investigated. Here, significant positive correlations were observed between the density of recruits and density of adult mussels and weights of empty shells. This indicates that the filtering mussels not only increase the mortality of larvae, but also serve as an important substrate reducing post-settling predation from benthic predators.     

Survey of mussel (Mytilus) species at Scottish shellfish farms

Mytilus trossulus and its hybrids with the native species Mytilus edulis and also Mytilus galloprovincialis have been recently detected in both farmed and natural populations of mussels in Scotland, adding complexity to the known M. edulis × M. galloprovincialis hybrid zone in Europe. Mytilus trossulus was first found in Scotland at aquaculture sites, where it was associated with significant losses in production and reductions in profitability. Mytilus trossulus and its hybrids have been identified at higher frequencies in farm stock than in natural intertidal populations, raising concerns about the potential wider impact of M. trossulus genotypes at mussel aquaculture sites in Scotland. The present study clarifies the composition of Mytilus species in cultivation at Scottish mussel aquaculture farms, by screening samples from 41 mussel aquaculture sites using a high-throughput real-time PCR methodology. Mytilus edulis alleles were detected at all sites. Mytilus galloprovincialis alleles were detected from samples collected at 39 sites, and M. trossulus alleles were found at five sites. Overall, M. trossulus genotypes were restricted in their geographical distribution. It is suggested that, in order to support the sustainability of the Scottish shellfish cultivation industry, the economic impact arising from the presence of M. trossulus could be limited through good management practice.     

A sensory and nutritional validation of open ocean mussels (Mytilus galloprovincialis Lmk.) cultured in SE Bay of Biscay (Basque Country) compared to their commercial counterparts from Galician Rías (Spain)

Mussel shell biometry, nutritional quality as well as consumer sensory evaluation of experimental open ocean cultured mussel Mytilus galloprovincialis (Lamarck 1819) were analyzed and compared to that of commercial mussels from Galician Rías available in the local market. Both mussel products were of the same commercial size. In this study, open ocean mussels were significantly higher and wider than those of Galician Rías. In addition, with the exception of ash content, both mussel products showed similar biochemical composition. Regarding fatty acid profiles, however, statistical differences were detected. These differences were not fully reflected in the sensory assessment. In terms of consumer acceptability, both mussel products were considered equally satisfactory.

     

Increased production of green mussels (Perna viridis) using longline culture and an economic comparison with stake culture on the north coast of Java,Indonesia

The effectiveness of green mussel (Perna viridis) cultivation was compared between longline culture and the traditional bamboo stake method using different mussel densities in a rural area on the north coast of Java, Indonesia. The study took place in a rural area about 2 km north‐east from the city of Semarang where unsustainable shrimp and fish pond culture in the past has led to massive mangrove loss, spiralling environmental degradation and socio‐economic disintegration. Mangrove‐friendly alternatives for a sustainable socio‐economic recovery of local livelihoods are urgently being sought. Longlines were more successful than the stake method in spat collection. Longlines also showed a small but significantly higher relative weight gain and specific growth rate for mussels than bamboo stakes. Mussels in lower densities showed higher survival and grew to larger individual sizes, but initial seeding density had no significant effect on relative weight gain or specific growth rate per stocking. Slightly lower set‐up costs and time investment and somewhat higher yields for longlines give an almost twofold higher income per time unit of own time invested by the farmer for longline culture over the traditional stake culture method. The profitability of mussel culture using the stake method is below the average hourly wage for skilled labour, but above that when using the longline method. We conclude that green mussel culture using the longline system is feasible as an alternative to less sustainable forms of livelihood for the local communities in mangrove areas.     

Implicit price of mussel characteristics in the auction market

This study explores desired and undesired characteristics of mussels in wholesale market by applying hedonic price analysis. Transaction data in auction market in Yerseke, the Netherlands, was used to estimate linear and semi-log price models. Meat content and size count, which are measured as the ratio of the weight of cooked meat to the total weight and the number of mussel per kg of raw mussels, respectively, are the most important characteristics determining the price. At the sample mean, if the meat content increases by 1%, farmers can get a premium price of 5.5 eurocents kg^?1 of raw mussel. Mussel lots with size counts below 50 pieces kg^?1 can command the highest implicit price of size. Processors prefer mussel lots in which the size of mussels is more or less heterogeneous. The impurity of mussel lots, which is measured by the percentage of tare, the amount of barnacles and limpets per kg of raw mussels are significant discounting factors on the price. The study also investigates the impact of farming locations and seasons on the price and the price trend during the period of 2002–2009.     

Simulating the dispersion of vertically migrating sprat larvae (Sprattus sprattus (L.)) in the German Bight with a circulation and transport model system

A model system consisting of two three-dimensional circulation models and a three-dimensional transport model is used to simulate the dispersal of sprat larvae (Sprattus sprattus (L.)) in the German Bight. A Northwest European shelf sea model simulates the currents of the North Sea and provides sea surface elevation data for the open boundaries of the German Bight circulation model. The German Bight circulation model has a horizontal grid resolution of 2.75 km and a vertical resolution of 5 m except for the bottom layer. The driving forces of the circulation models are the M2-tide, six-hourly time-dependent wind stress and air pressure fields as well as monthly climatological density fields. The simulated currents serve as input to the transport model. The model area, grid size and the vertical resolution of the transport model are in accordance with the German Bight circulation model. The transport model simulates advection and diffusion using a Monte Carlo method. Furthermore it incorporates a simulation of active vertical movement of the larvae. The vertical migration pattern is dependent on the time of day and size of the larvae and is based on field data from the German Bight. Horizontal larvae distribution data, gained from two out of five field surveys carried out in the German Bight during spring and summer 1991, are used as initial values for the starting points of the tracers in the transport model. Simulated tracer distributions are compared with larval distributions observed during subsequent cruises about 3 weeks later. Discrepancies and similarities between tracer and larval distributions are discussed.     

Effects of seed size and density on growth, tissue-to-shell ratio and survival of cultivated mussels (Mytilus edulis) in Prince Edward Island, Canada

In suspended aquaculture, the size of mussel seed and the density at which these mussels are placed in socks are two important factors affecting mussel production. However, the effect of these two factors has yet to be examined simultaneously. We conducted two large-scale field experiments to assess the effect of seed size and initial density on growth, tissue-to-shell ratio and survival of blue mussels (Mytilus edulis) grown on longlines. Experimental mussel sites were set up during the autumn of two consecutive years in two bays on the north shore of Prince Edward Island, Canada. At each site, socks containing combinations of three seed sizes (small, medium and large) at two initial densities (low and high) were deployed and monitored over time. Small seed grew faster than large seed and often reached commercial size in the same time period. Furthermore, initial density generally did not affect shell growth. During the pre-spawning period following the autumn deployment, seed at low initial density had a higher tissue-to-shell ratio than seed at high initial density, especially for large seed. This effect of initial density disappeared in early summer. Early in the experiments (< about 10 months), mussel survival on socks was affected by seed size only: small seed generally had lower survival rates than larger seed. Late in the experiments (> 10 months), there appeared to be an interaction between seed size and initial density on mussel survival: survival of small seed generally decreased with increasing initial density, while survival of large seed was not affected by initial density. Since large seed tended to be packed at lower initial density than small seed, lack of crowding was likely responsible for the absence of density-dependent loss. Our study thus assessed different seeding strategies, and results were generally consistent across years and sites.     

An Economic Analysis of Freshwater Prawn, Macrobrachium rosenbergii, Farming in Mymensingh, Bangladesh

This paper deals with production systems, cost structure, and profitability of freshwater prawn, Macrobrachium rosenbergii, farming in a new area of Mymensingh district in the north‐central part of Bangladesh. In the study area, prawn farming practice is still extensive, and only a few farmers (20%) cultivate semiintensively. The costs and returns of extensive and semiintensive farming systems are compared. All farmers in different farming systems made a profit, with seed and feed dominating variable costs. Considerable variation in production costs and profitability was observed. Based on the Cobb–Douglas production function model, return to scale indicates that there is scope to increase production and income from prawn farms in extensive and semiintensive systems by applying more inputs (i.e., seed, feed, and fertilizer).     

Seasonal variations of physiological parameters in the blue mussel mytilus spp. from farm sites of eastern Quebec

A seasonal monitoring of indigenous (Gaspé Bay, Carleton, Havre-St-Pierre, Magdalen Islands and Blanc-Sablon) and transplanted (Gaspé Bay, Carleton, Havre-St-Pierre) mussels from different farm sites of Eastern Quebec allowed us to study mussel physiology as a function of environmental factors. A positive influence of phytoplankton cell concentration and temperature on the reproductive cycle was discovered even if no significant relationship has been showed because of the fragmented pattern of gametogenesis. A decrease of digestive gland index (DGI) was observed during gametogenesis. Development of gametes needs much energy and its great influence on digestive gland weight prevented us to correlate mussel growth with environmental factors. A decrease of phagocytic activity was observed in each site in midsummer, concomitantly to the most active spawning period. A significant positive correlation was remarked between maturity index in males and phagocytosis. A decrease of phagocytic activity could then have a direct impact on mussel population since it occurred during high temperature period when mussels had to face spawning, bacterial developments and diseases. It appeared in our study that reproductive cycle is a key event in mussel physiology and important for mussel farmers to follow-up. In the near future, we intend to develop and validate reliable indicators of the reproductive cycle in cultured mussels.     

大亚湾翡翠贻贝增养殖技术及效果的研究

１９９２－１９９４年在大亚湾西北部的哑铃湾开展翡翠贻贝的延绳式及筏式吊养增养殖试验，养殖面积约９．１ｈａ，总产量４０６ｔ。种苗来源中有４０％为人工培育苗，其余为天然苗。两种吊养方式的贻贝经１至１．５年的养殖，壳长可达７０－８０ｍｍ。研究结果表明，人工苗可补充天然苗的不足，延绳式为最佳养殖方法。     

Settlement and growth of the mussels (Mytilusgalloprovincialis,Lamarck, 1819) on different collectors suspended from an offshore submerged longline system in the Black Sea

A study of spat settlement of a submerged longline mussel culture system was carried out in Sinop area, Black Sea, between May 2008 and May 2009. The effects of six different types of collectors on spat settlement and growth were investigated. Six different types of spat settlement rope were used as polypropylene ropes with 18 mm diameter, 18 mm diameter timeworn silk rope, 22 mm diameter rope made from old hawser (OSR), 22 mm diameter ropes made from old anchovy net without pegs, 18 mm diameter old used nylon ropes and 18 mm diameter tasselled polypropylene ropes. Monthly temperature, salinity, chlorophyll‐a, total suspended matter, inorganic matter and organic matter were determined during the experimental period. The best settlement was observed on the OSR type when measured per metre (3450.00 ± 125.83 ind m^?1). Consequently, the findings showed that settlement preference of spat occurred according to rope structure, and if ropes are designed to combine numerous well‐fixed tassels, spat settlement can increase. Spat growth was affected by environmental factors and rope structure. In addition, the study revealed a negative relationship between density and growth.