Microbiological controls across the productive cycle of Dicentrarchus labrax L. and Sparus aurata L.: a study from the environment to the final product

The microbiological quality of water, sediments and seafood products of three Sicilian marine fish farms (Castellammare Gulf, Capo d'Orlando and Porto Palo) was investigated in order to draw a complete picture of the health conditions from the start (environment) to the end (seafood product) of the productive cycle. Before the beginning of fish farming, low concentrations of faecal contamination indicators (faecal coliforms, Escherichia coli, enterococci) were found in the water of each examined area. Due to the enhanced organic load released from cages, the set‐up of fish farming significantly altered the distribution of faecal indicators and sometimes that of halophilic vibrios in the pelagic compartment. Significant differences in the density of heterotrophic bacteria were sometimes recorded at the sediment level. Despite this increase in microbial abundance, the microbiological conditions remained acceptable for the productive process. Pathogens (Salmonella spp., Vibrio parahaemolyticus, Listeria monocytogenes, Staphylococcus aureus) were mostly absent in seafood products. The study underlines that the achievement of good quality levels in aquaculture strongly depends on the conformity of the rearing environment to qualitative microbiological standards, highlighting the importance of sanitary controls along the different steps of the productive cycle.     

Sea cucumber habitat differentiation and site retention as determined by intraspecific stable isotope variation

Stable carbon and nitrogen isotope ratios (δ¹³C/δ¹⁵N) were assessed as a means to ascertain the recent in situ feeding history of the common New Zealand sea cucumber Australostichopus mollis in relation to nutrient enrichment from a longline green‐lipped mussel (Perna canaliculus) farm in Northern New Zealand. δ¹³C and δ¹⁵N isotopic signatures and the ratios of sea cucumbers sampled from within the impact footprint of the mussel farm were compared with those of sea cucumbers residing on adjacent natural reefs. Sea cucumbers from beneath mussel farming longlines had significantly different δ¹³C stable isotope signatures in comparison with sea cucumbers collected from neighbouring natural reef habitats. This difference supports the hypothesis that sea cucumbers in the same bay maintain distinctly different feeding histories, with those residing beneath mussel farming longlines deriving tissue carbon from sediment impacted by farming activities. This hypothesis is further supported by the finding that the isotope signature of sediment collected from beneath the mussel farm is consistent with the expectation that sea cucumbers were feeding on and consuming sediment enriched with bivalve waste (faeces and pseudo‐faeces). In contrast, the nitrogen stable isotope signature (δ¹⁵N) was found to be similar between sites for both sea cucumbers and assumed food sources. Both findings lend support to the viability of future sea cucumber/green‐lipped mussel farm polyculture systems. Sea cucumbers in different locations (mussel farm, natural reef) possessed distinctly different isotope signatures, suggesting that mixing of sea ranched sea cucumbers with natural reef populations would be negligible or non‐existent. Similarities between the isotope signatures in low metabolic tissue of sea cucumbers residing at the mussel farm site to that of mussel farm‐impacted sediment suggest that cucumbers beneath mussel farms appear to have high rates of retention at the farm site.     

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.     

The effect of C/N ratio on bacterial community and water quality in a mussel‐fish integrated system

A 30‐day experiment was conducted to evaluate the effect of C/N ratio on water quality and bacterial community in an integrated system comprising one molluscan species (pearl mussel Hyriopsis cumingii) and two fish species (gibel carp Carassius gibelio and silver carp Hypophthalmichthys molitrix) at five C/N ratios (6, 8, 10, 12 and 14). The mussel and fishes were reared in the experimental tanks (400 L), but gibel carp received formulated feed. Water quality in the experimental tanks was analysed on day 0, 10, 20 and 30, and bacterial community in the water column and sediment was analysed on day 30. Total nitrogen, total phosphorus and total organic carbon accumulated in the tanks over time. Ammonia and nitrite decreased with the increase in C/N ratio. Bacterial community in the water column and sediment changed at the phylum and genus levels with the increase in C/N ratio, and the critical C/N ratio causing a functional shift of bacterial community occurred at 10 in water column and 12 in sediment. The increase in C/N ratio benefited the growth of both potential probiotics and pathogenic bacteria. The high C/N ratio enhanced the bacterial functions of chemoheterotrophy and hydrocarbon degradation, but depressed the functions of nitrification and denitrification in the water column and sediment respectively. This study reveals that the C/N ratio can be used as a tool to manipulate the bacterial community and water quality in the mussel‐fish integrated system.     

固定化微生物修复养殖池塘污染底泥的围隔试验

摘要：通过测定上覆水的多项水质指标、底泥总有机碳(TOC)、底泥生物降解能力(G值)、底泥异养细菌数和反硫化细菌数等指标值,在野外实验围隔条件下比较了固定化微生物和游离微生物（FR-M）对污染底质的生物修复能力。微生物固定所用载体包括：纤维网状活性炭,生物活性炭,沸石和硅藻土(相应的固定化微生物分别标记为FC-M、 BC-M、ZE-M和DI-M组)。结果显示：固定化微生物对围隔内水质有间接影响,试验后期固定化微生物组（ZE-M、DI-M和FC-M组）的上覆水硝氮浓度显著高于对照组;BC-M组和ZE-M组上覆水中的COD值显著低于游离微生物组(FR-M)和对照组,说明固定化微生物有效削减了水底界面还原性物质的污染程度;与游离微生物或对照组相比,固定化微生物组（FC-M组、DI-M 组和ZE-M组）能更有效地降解底泥有机质。固定化微生物对底泥生物降解能力（G值）的影响明显,实验后期固定化微生物组（（BC-M组、DI-M组和ZE-M组）的G值均显著高于对照组和游离微生物组,说明固定化微生物技术的运用显著提高了围隔底泥的生物降解能力;固定化微生物对围隔内底泥异养细菌总数影响不显著,可能是由于底泥微生物群落结构受其它多种因子的综合影响所致。固定化微生物对底泥反硫化细菌影响显著,与对照组和游离微生物组相比,固定化微生物（尤其是ZE-M和BC-M组）能更有效地减少围隔底泥反硫化细菌数。本实验结果显示,利用载体固定微生物技术能显著提高微生物对污染底质的生物修复能力,其中以ZE-M和BC-M组效果最好。     

高产鱼池中异养细菌的初步研究

对无锡市效区“河埒渔业一队”典型高产鱼池中异养细菌种类、数量及群落组成的分析测定,它表明在1984年3月至10月试验期间,试验鱼池水体中总细菌数和异养细菌数分别在1.30×10~5～15.90×10~5个/ml和1.56×10~4～14.50×10~4个/ml。鱼池淤泥中总细菌数和异常细菌数分别在1.20×10~6～68.0×10~5个/克和1.94×10~5～19.90×10~5个/克。同时经分析得知,试验鱼池中细菌数量的波动与鱼池水温等理化因子各有不同的相关关系。试验鱼池水体中共分离出11个属的异养细菌,其中优势菌为氮单胞菌属(Azomonas)等具固氮能力的菌属;淤泥中共分离出8个属的异养细菌,其中优势菌为芽孢杆菌属(Bacillus)等革兰氏阳性菌属。假单胞菌属(Pseudomonas)的细菌普遍存在于鱼池的水体及淤泥中。试验表明,高产鱼池中的细菌数量变化有一定规律性,细菌数量及异养细菌的群落组成与鱼池的鱼产量有一定的关系。     

Behavioural interactions of seabirds with suspended mussel longlines

Increased abundances of a number of seabird species have been found in areas of mussel longline aquaculture (compared to control sites) in a recent study at Bantry Bay, southwest Ireland. The aim of this study was to investigate whether this form of mussel aquaculture also affects the activity budgets and foraging behaviour of these seabirds. Scan-sampling was used to compare seabird activity budgets between three areas of mussel longline aquaculture and three control sites. Foraging activities of Great-Northern Divers Gavia immer, an Annex 1 species under the Euopean Union's Birds Directive, were also compared between sites using focal sampling. The behaviour of gulls (Larus sp.), Cormorants Phalacrocorax carbo, Shags Phalacrocorax aristotelis and Great-Northern Divers (but not auks, Alcidae) differed significantly between areas of mussel aquaculture and control sites in this study. Mussel suspension buoys were heavily utilized by gulls, cormorants and shags as safe perching platforms for preening activities. Gulls also fed extensively on epifauna attached to the buoys. Great-Northern Divers spent more time snorkelling (head submerged in search of food) in mussel sites than in the control sites, however dive duration and visible foraging success rates did not differ significantly between sites. Overall, the environmental impact of mussel suspension culture appears to be positive or neutral on marine bird species occurring at this study site.     

固定化微生物在凡纳滨对虾养成池中的应用

通过监测池塘水体藻类群落组成、多项水质指标、底泥总有机碳(TOC)和底泥异养细菌数等指标值,研究了固定化微生物对凡纳滨对虾生产性养殖池塘水质调控和污染底泥的修复能力,微生物固定所用载体为改良沸石和生物活性炭(相应的固定化微生物分别记为ZE-M组和BE-M组)。试验结果显示,处理组(ZE-M组和BE-M组)池塘水体中藻类组成呈多元化,隐藻、蓝藻和绿藻数量比较接近,而对照组则是蓝藻占绝对优势。试验过程中,对照池的氨氮浓度和COD呈直线上升,而处理组氨氮浓度和COD的增长幅度缓慢,ZE-M、BC-M载体微生物的使用是产生差异的直接原因。对照组和处理组的其它水质指标变化规律及差异性不明显,可能是由于池塘水体由诸多不确定因素影响所致。固定化微生物对池塘底泥TOC含量和异养细菌数的影响显著(P<0.05),试验过程中,试验组和对照组池塘底泥TOC含量随着养殖时间均有增加的趋势,但对照组这一趋势更加明显;试验初期,各组表层底泥中的异养细菌数量在3.367×105～8.60×105CFU/g范围内,试验结束时增长到85×105～393.7×105CFU/g。处理组和对照组的异养细菌差异显著(P<0.05),其中ZE-M处理组...     

Heavy metal concentrations and sediment quality of a cage farm on Lake Volta,Ghana

This study involved the determination of sediment quality and heavy metals in the water column and bottom sediment of a selected cage fish farm in Lake Volta, to assess the potential impact of metals and organic matter pollution on the lake due to cage fish farming. Sediment analysis indicated that the texture of all sampling sites was sandy clay loam with sand dominating with a range of 31.5%–81.2%. The organic matter (TOM) ranged from 4.42%–8.89%, while organic carbon (TOC) was from 2.57%–5.22%. Total nitrogen (TN) fluctuated between 0.22% and 0.45%; total phosphate ranged between 0.22% and 5.30%. The TOC, TOM and TN content in the farm sediment were significantly lower than those of the reference sites (ANOVA, p < .05). Lead, copper, cadmium and selenium were not detected in the water. The results revealed that heavy metal concentrations in the water column and sediments were low and within tolerable levels, indicating no influence of metals from fish feed was observed on the lake water quality. However, the farm seemed to have moderate impact on sediment quality from organic matter. Water and sediment quality monitoring should be embarked upon periodically to ensure sustainable cage culture in the Lake Volta.     

枸杞岛贻贝养殖水域碳氮磷分布格局

于2013年贻贝成熟期和幼苗期对枸杞岛贻贝筏式养殖水域营养分布和碳分布格局开展相关实验。结果表明:从生态健康角度,夏季成熟期的贻贝养殖造成养殖海域氮、磷营养盐浓度升高,尤其是无机氮浓度显著高于非养殖区(P<0.05),养殖区处于受磷限制性的重富营养化,对其水体健康产生一定压力;秋季幼苗期贻贝养殖使养殖海域氮、磷浓度均降低,尤其是无机氮浓度显著低于非养殖区(P<0.05),与夏季分布格局相反,对水体有净化作用。从生态效应看,贻贝养殖使表层水体中溶解无机碳浓度显著低于非养殖区(P<0.05),产生碳汇效应;同时,贻贝养殖使水体中溶解有机碳浓度显著高于非养殖区(P<0.05),由于丰富的氮营养盐,溶解有机碳处于不稳定态,为碳源。因此,成熟期与幼苗期贻贝养殖对其水域健康产生不同作用,养殖的碳汇、碳源还有待进一步的系统研究。     

Faecal coliforms in pond water, sediments and hybrid tilapia Oreochromis niloticus×Oreochromis aureus in Saudi Arabia

Total bacterial load, total coliforms faecal coliforms in pond water, sediment, intestine of hybrid tilapia Oreochromis niloticus×Oreochromis aureus and pigeon Columba livia faeces were investigated monthly over a period of 1 year from July 1999 to June 2000. Fish were collected randomly by a cast net. Samples were analysed for coliforms using the multiple‐tube fermentation technique. Results showed total viable bacterial counts in the pond water, sediment, intestine of tilapia and pigeon faeces ranging from 1.8±0.9×10² to 6.0±1.2×10⁴ cfu mL^?1, 3.2±1.2×10⁵ to 2.8±1.5×10⁷ cfu g^?1, 8.2±1.6×10⁵ to 9.9±1.5×10⁷ cfu g^?11.0±0.4×10⁷to9.7±0.2×10⁹ cfu g^?1respectively. The most probable number (MPN) of coliforms and faecal coliforms ranged from 287±12 to ≥1600±0 100 mL^?1 in pond water; the MPN ranges for sediment, tilapia intestine and pigeon faeces were 257±29 to ≥1100±0 g^?1, 237±46 to ≥1100±0 g^?1 and 403±98 to ≥1100±0 g^?1 respectively. The abundance of normal bacteria coliforms was greater in the warm months than in the cold months. Ground water was free from any sort of coliform organisms, and there were no sources of human faecal matter in the pond. So, it is clear that faecal coliforms from pigeon faeces significantly contaminated (P<0.05) the ponds and tilapia intestines. Escherichia coli was the only coliform organism found in pond water, sediment, intestine of tilapia and pigeon faeces.     

Benthic microbial indicators of fish farm impact in a coastal area of the Tyrrhenian Sea

We studied the impact of organic loads due to the biodeposition of a fish farm in a non-impacted coastal area of the Tyrrhenian Sea (Western Mediterranean). Sediment chemistry and benthic microbial community were investigated from July 1997 to February 1998 on monthly basis at two stations: one was located under the fish farm, while the second was about 1 km away, and served as a reference site. The presence of the cage induced rapid changes in the benthic conditions: the sediments were rapidly (after 6 weeks) reduced. A significant accumulation of biopolymeric carbon was observed beneath the cage both 2 weeks after the initial cage deployment, on non-impacted sediments, and 5–7 months after, and appeared to be related to the fish farm production cycle. The density of microbial communities beneath the fish farm increased only during the first month of farming activity (July) and partially 7 months after cage disposal (i.e. in January), when there was a significant sediment organic enrichment. Additional evidence of rapid impact of the fish farm on the benthic bacterial communities is provided by the increase in the numbers of autofluorescent microbial cells. The photosynthetic eukaryotic cells displayed a highly reduced contribution to total autofluorescent microbial density, indicating that their decrease is related with biopolymeric carbon accumulation, and probably was due also to “shadow effect” induced by suspended material, coming from the fish farm, on the environment below. We propose here, to apply the ratio of culturable heterotrophic bacteria to microbial direct counts (CFU/MDC) to detect fish farm impact. In cage sediments, organic enrichment and the consequent modification of the characteristics of the benthic environment, determined an increase in aerobic heterotrophic bacteria and vibrio density indicating that they are efficient colonizers of organic-rich sediments. Densities of Escherichia coli and Enterococci were not significantly higher than in the reference site, and are likely of terrestrial origin. Thus they cannot be used as specific indicators of fish farm impact.     

Bacteria in shrimp pond sediments: their role in mineralizing nutrients and some suggested sampling strategies

Strategies for sampling sediment bacteria were examined in intensive shrimp. Penaeus monodon (Fabririus), ponds in tropical Australia. Stratified sampling of bacteria at the end of the production season showed that the pond centre, containing flocculated sludge, had significantly higher bacterial counts (15.5 × 10⁹ g-¹ dw) than the pond periphery (8.1 × 10⁹g^?1 dw), where the action of aerators had swept the pond floor. The variation in bacterial counts between these two zones within a pond was higher than that between sites within each zone or between ponds. Therefore, sampling effort should be focused within these zones; for example, sampling two ponds at six locations within each of the two zones resulted in a coefficient of variation of ± 5%. Bacterial numbers in the sediment were highly correlated with sediment grain size, probably because eroded soil particles and organic waste both accumulated in the centre of the pond. Despite high inputs of organic matter added to the ponds, principally as pelleted feeds, the mean bacterial numbers and nutrient concentrations (i.e. organic carbon, nitrogen and phosphorus) in the sediment were similar to those found in mangrove sediments. This suggests that bacteria are rapidly remineralizing particulates into soluble compounds. Bacterial numbers were highly correlated with organic carbon and total kjeldahl nitrogen in the sediment, suggesting that these were limiting factors to bacterial growth.     

Testing the potential for improving quality of sediments impacted by mussel farms using bioturbating polychaete worms

Biodeposits from farmed mussels severely influence the biogeochemistry of sediments by increasing the levels of organic matter (OM). Mitigation of such negative impacts is important for the development of sustainable aquaculture operations. As a step towards developing methods for remediation of coastal sediments affected by mussel farming, the effects of the polychaete, Hediste diversicolor was evaluated experimentally. In a series of field‐ and laboratory experiments we tested hypotheses about the effects of polychaetes on sediment oxygen consumption, nutrient fluxes and sulphide pools under different polychaete densities and sedimentation regimes. The experimental results support the idea that polychaetes can mitigate negative effects on the benthic environment beneath mussel farms. H. diversicolor oxidized the sediment and generally enhanced the oxygen consumption, and thus the decomposition of OM. The accumulation of pore water sulphides were reduced and fluxes of nutrients across the sediment‐water interface increased. Additional calculations suggest that the effects of polychaetes were mainly indirect and driven by increased microbial activity due to the borrowing activity of the polychaetes. Trends of increasing decomposition with increasing polychaete density suggest that the decomposition could be further enhanced by higher densities. Overall, we concluded that H. diversicolor is a potentially strong candidate for remediation of mussel farm sediments. The results show that sediments inhabited by H. diversicolor have high assimilative capacity of OM and oxygen conditions are significantly improved following the addition of polychaetes at naturally occurring densities. However, technological developments are needed in order to allow the approach to be used in practice.     

Floc and sediment properties and their environmental distribution from a marine fish farm

Open ocean pen aquacultural operations are leaky systems with potential environmental impacts of metabolic excretions products, feed additives, and anti‐fouling agents. This study analysed the water–sediment interface along a horizontal transect away from a fish farm, noting variations between water, floc, and sediment properties. The properties examined included nitrogen (N), phosphorus (P), carbon (C), sulphur (S), and trace element content, as well as heterotrophic bacteria populations. C, N, labile P, NH₄, Ca, and Zn were elevated in surface sediments at the farm in comparison with sites 100 and 300 m away. The flocs had higher levels of Mg, K, and heterotrophic bacteria than adjacent sediments, indicating the importance of the microbial communities in flocs. The flocs were important in their role as a retention and potential transport mechanism for metals, increasing in concentration of Al, Fe, and Mn with distance from the farm.     

Quality Changes in Gamma Irradiated Marinades of Anchovy (Engraulis anchoita) During Refrigerated Storage

The effect of gamma irradiation (0, 1.8, and 3.3 kGy) on the microbiological, chemical, and color characteristics of marinated (7% acetic acid and 10% NaCl) and vacuum-packed anchovy fillets was analyzed during 20 months of refrigerated storage (4 ± 1°C). Acidity, pH, water activity (a_w), total volatile basic nitrogen (TVBN), lipid oxidation, and color parameters were determined. Mesophilic and psychrotrophic bacteria, sulphite-reducing clostridia, total and fecal coliforms, Staphylococcus spp., yeasts, and molds were investigated. Gamma irradiation reduced the initial mesophilic bacterial counts and inhibited mesophils growth during 20 months. As a result, the production of TVBN during storage was lower in irradiated samples than in control. Also, lipid oxidation was lower in irradiated samples than in nonirradiated. The color of anchovy fillets was not affected by the irradiation treatment. Even if nonirradiated anchovy fillets presented a high stability in comparison with the traditional product (in flasks with vegetable oil and spices), gamma irradiation improved the microbiological and chemical quality of anchovy fillet marinades without inducing changes on its characteristic color for 20 months.     

Heterotrophic versus mixed BFT system: Impacts on water use,suspended solids production and growth performance of Litopenaeus vannamei

The Biofloc Technology System (BFT) is characterized by stimulating the development of a microbial community that acts mainly in the maintenance of water quality but also promotes other benefits such as increased productivity, biosafety and serves as a supplementary source of food for reared animals. Two main groups of bacteria are involved in nitrogen removal in this system: heterotrophic bacteria and autotrophic nitrifying bacteria, present in the aggregates. Different fertilization techniques can be used for the formation and maintenance of bioflocs, depending on which group of bacteria the predominance is preferred. This study aimed to analyze the effect of different organic fertilization techniques on the bioflocs establishment, amount of water used, the production of suspended solids and the growth performance of Litopenaeus vannamei reared in the BFT System. Shrimp juveniles were stocked in 150-liter tanks at a stocking density of 300 shrimps/m³. Three treatments (in triplicate) were tested using different fertilization techniques: 1) without supplementary organic fertilization; 2) organic fertilization according to nominal ammonia reading (heterotrophic/chemoautotrophic = “mixed” system) and 3) organic fertilization according to estimated ammonia production (heterotrophic). The temperature, salinity, dissolved oxygen, pH, ammonia, nitrite, nitrate, alkalinity and total suspended solids (TSS) of the water were monitored. The water quality parameters were influenced by the treatments with differences found in the concentrations of ammonia, nitrite, nitrate, pH, alkalinity and TSS. Ammonia levels were higher in control treatment since no organic fertilization was performed. Nitrite levels were lower in heterotrophic system since the nitrifying pathway was suppressed due to daily fertilization, also resulting in lower nitrate levels. There were significant differences in the growth performance parameters, with the highest final weight and yield, as well as the lowest FCR, found in the mixed treatment. There were no significant differences among survival. The mixed system treatment used less water during production cycle compared to other treatments while the volume of solids removed was almost four times greater in the heterotrophic treatment compared to the others. These results show that adopting a mixed heterotrophic/chemoautotrophic biofloc system improves shrimp growth performance, optimize water use and decrease solids production.     

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.     

Effect of water exchange on effluent and sediment characteristics and on partial nitrogen budget in semi-intensive shrimp ponds in New Caledonia

An experiment was conducted in six earthen ponds with 20 shrimps m^?2Litopenaeus stylirostris (Stimpson) during the warm season in New Caledonia to study the dynamics of wastes in relation with water exchange rate (WER). The nitrogen budget was established, taking into account the different forms of nitrogen in the water, sediment, feed and shrimp. Data from a wide range of treatments applied in unreplicated ponds were treated using regression analysis to establish the relationship between WER and partial nitrogen budget, sediment characteristics and shrimp performance. To compare effluent quality between treatments during the season, data were analysed using the non‐parametric sign test. The water outflow was characterized by a decrease in the concentrations of N‐mineral forms (TAN, NO₂^?–NO₃^?), an increase in the concentration of organic soluble and sestonic organic forms (expressed in terms of particulate nitrogen, particulate organic carbon, chlorophyll a) compared with the water inflow. Increasing WER increased the amount of exported wastes and mainly in the organic forms and TAN can be considered as negligible. The nitrogen budget showed that 19–46% of nitrogen input (feed+water) was exported into the coastal environment. The results showed that the quality of the sediment decreased as WER decreased. The potential negative impact of the developing industry in New Caledonia on the costal environment could be partially reduced in a first step by decreasing WER. However, if applied in the farms, this practice should be linked to a close survey of the evolution of sediment quality.     

Freshwater Pearl Culture Technology Development in India

ABSTRACT

Development of science and technology of cultured pearl production in a freshwater environment in India is described. Distribution of Indian pearl mussels, pond mussel Lamellidens marginalis, paddy field mussel L. corrianus, and riverine mussel Parreysia corrugata in relation to environmental variables such as type of soil, nature of sediment substratum, presence or absence of macrophytes (Eichhornia sp., Nechamandra sp., andNymphaea sp.) is described. Food and feeding of the mussels, together with density aspects in culture conditions are discussed. Mussel breeding including specificity in fish hosts, and mussel larval parasitic relationships are discussed. Basic steps involved in indigenous freshwater pearl culture technology are summarized. Pearl culture grafting procedures such as mantle cavity, mantle tissue and gonadal implantation along with different pearl products are also described.