Current status of parasitic ciliates Chilodonella spp. (Phyllopharyngea: Chilodonellidae) in freshwater fish aquaculture

Freshwater fish farming contributes to more than two‐thirds of global aquaculture production. Parasitic ciliates are one of the largest causes of production loss in freshwater farmed fishes, with species from the genus Chilodonella being particularly problematic. While Chilodonella spp. include ‘free‐living’ fauna, some species are involved in mortality events of fish, particularly in high‐density aquaculture. Indeed, chilodonellosis causes major productivity losses in over 16 species of farmed freshwater fishes in more than 14 countries. Traditionally, Chilodonella species are identified based on morphological features; however, the genus comprises yet uncharacterized cryptic species, which indicates the necessity for molecular diagnostic methods. This review synthesizes current knowledge on the biology, ecology and geographic distribution of harmful Chilodonella spp. and examines pathological signs, diagnostic methods and treatments. Recent advances in molecular diagnostics and the ability to culture Chilodonella spp. in vitro will enable the development of preventative management practices and sustained freshwater fish aquaculture production.     

大型养殖工船运营实践与展望

溶解氧 (Dissolved oxygen, DO) 是影响养殖工船水产品健康生长的重要因素,准确预测DO对提高水产品产量和品质具有重要意义。为提高DO预测精度,以卵形鲳鲹 (Trachinotus ovatus) 养殖试验采集的数据为样本,使用卷积神经网络 (Convolutional neural network, CNN) 和门控循环单元 (Gated recurrent unit, GRU) 方法建立养殖工船水体DO预测混合模型,通过Pearsons相关性分析,选用DO、温度、pH和循环水流量4个预测因子进行训练和校准,预测了DO含量。通过与CNN、GRU和长短期记忆 (Long short-term memory, LSTM) 模型进行对比,所建模型在各项评价指标中的性能均最优,其均方根误差 (Root mean square error, RMSE)、平均绝对误差 (Mean absolute error, MAE) 和决定系数R²分别为0.119、0.084和0.976。结果表明,所建模型的预测精度最高,可以满足养殖工船实际生产中对DO预测的需求,为养殖工船生产过程中DO的监控和预警提供参考。     

Synthetic fibre as biological support in freshwater recirculating aquaculture systems (RAS)

The aim of this study was to evaluate the use of synthetic fibre as a biological support for the adhesion of nitrifying bacteria in an aquaculture recirculation system (RAS). It was developed from three assays over 120 days. In the first assay, the synthetic fibres used as biological support were introduced in tanks of biological filtration of the system for posterior respirometry analysis and scanning electron microscopy (SEM). Respirometry and SEM were performed 10 days after inoculation with nitrifying microorganisms. Water quality parameters were monitored daily, and the respirometry showed that the bacteria in this assay were consuming the following amounts of ammonium: concentrations [C1]35.369 mg NH₃/L, R² = 0.9912; [C2]51.628 mg NH₃/L, R² = 0.9883; [C3]79.494 mg NH₃/L, R² = 0.986; and [C4]215.225 mg NH₃L, R² = 0.9934. In the second assay, a 1920-L tank was stocked with 120 Nile tilapia, Oreochromis niloticus, with an initial weight 32.11 ± 7.6 g and a biomass of 3.8 kg. After 60 days, the tank and its contents were assessed to evaluate zootechnical parameters and physical–chemical parameters of water quality. From these results, a third assay was developed in which the biomass of fish was increased to challenge the recirculation system. The tank was stocked with 480 jundiá Rhamdia quelen (initial weight 11.34 ± 2.4 g and biomass 5.4 kg) for 60 days. In both the tilapia and jundiá assays, the fish were fed four times per day with a commercial diet of 35% crude protein and 42% crude protein, respectively, at 5% of each individual fish’s body weight. At the end of the zootechnical assays, the synthetic fibres used showed efficient biological support for bacterial growth, as confirmed by scanning electron microscopy. The fibres also demonstrated maintenance of the water quality, which allowed good fish growth in the recirculating aquaculture system, and the maintenance of up to 11.19 kg/m³ of biomass of fish.     

Evaluation of antimicrobial products used in tilapia (Oreochromis spp.) and whiteleg shrimp (Litopenaeus vannamei) aquaculture

Despite the importance of aquaculture increases for feeding the growing world population, professional farm management and proper use of aquaculture products or drugs are needed. It is important to know the quality of commercial antimicrobial products on the market while there is wide use of antimicrobials to treat fish diseases. The most commonly used antimicrobial products were identified from a previous survey, included amoxicillin, enrofloxacin, florfenicol, sulphadiazine, sulphamonomethoxine and sulphadimidine. Eight local chemical supply shops were randomly sampled in representative aquaculture areas in Maoming and Zhanjiang districts of south China in 2013. In this study, only eight products contained active substances within ±10% of the concentration declared on the product label among the 30 different most used commercial products; while six products did not contain any of the declared antimicrobials. Three products without labels were sold as ‘pure antimicrobial’ and had high concentrations of active antimicrobials. Furthermore, most products only provided ambiguous information on the packages on both antimicrobial usage and dosage; and only one product stated how to prepare medicated feed which is important for efficient usage. The results of this study showed that the aquaculture antimicrobial products sold on the market were of low quality and thus compromised effective fish disease treatment. Moreover, insufficient information on products’ labels would provide limited instruction on correct antimicrobial usage. Inspection and supervision by both private companies and the government's sector require strengthening.     

Optimization of blue mussel (Mytilus edulis) seed culture using recirculation aquaculture systems

By introducing recirculation aquaculture systems (RAS) in the nursery phase of the blue mussel (Mytilus edulis) (17–18 mm), we aimed at a similar growth and survival and a similar water quality compared to the commonly used flow‐through systems (FTS). To calculate water flow and size of the biofilter, a series of experiments were done to determine clearance rate (9.26 mL min^?1), pseudo faeces threshold (60 000 cells Pavlova lutheri mL^?1), nitrogen production (0.00065 mg TAN h^?1 ind^?1 and 1.6 × 10^?5 mg NO₂–N h^?1 ind^?1) and oxygen consumption (0.03 ± 0.01 mg O₂ h^?1 ind^?1). RAS showed no significant differences in water quality (0.06 mg TAN L^?1; 7.7 mg O₂ L^?1) and growth performance of mussel seed specific growth rate (SGR = 5% day^?1) after the experimental period of 4 weeks compared with FTS. The low water refreshment, 10% per day, as well as the constant chlorophyll concentrations (9.76 ± 1.06 μg L^?1), suggests the potential of RAS as culture system for mussel seed.     

A review of methods for Centropomus spp. (snooks) aquaculture and recommendations for the establishment of their culture in Latin America

The positive features of Centropomids and Latids for cultivation are analysed and highlighted. The main life cycle characteristics as well as market prices and demands are presented. Good growth, highly efficient food conversion ratios and energy utilization allow very high biomass yields per unit volume in nursery and grow‐out systems. They have shown notable tolerances to main environmental conditions, as well as considerable versatility in adapting to culture systems (cages, ponds and tanks), and culture intensity (extensive, semi‐intensive, intensive and superintensive), especially in estuarine and coastal sites and ponds. These positive features provide them with a high culture potential. A general summary of their culture is presented, based on the commercial cultivation of the Asian sea bass or barramundi Lates calcarifer as well as the experimental and pilot‐scale results from the main American species. The importance of hatchery fry production as an essential culture pre‐requisite is emphasized, in addition to an analysis of the main difficulties and constraints for future development.     

双船表层浒苔围拖网实船试验报告

根据浒苔聚集、漂浮分布特点,研制了表层浒苔围拖网。经海上试验表明,本设计网具完全达到了快速、高效的浒苔打捞目标。     

Loads applied to aquaculture nets by the biting behaviour of Atlantic cod (Gadus morhua)

Atlantic cod (Gadus morhua) bite at netting materials in sea-cages, which is known to weaken and destroy net materials, contribute to the formation of net holes and lead to escapes. We determined the lateral pulling forces applied to nets through biting by cod in a laboratory set-up. A sensor for automatic logging of the lateral pulling force was used to obtain data for over 1000 undisturbed, objectively collected biting events. Lateral pull force varied between cod of different size (180 and 610 g) and different net types, ranging from 0.9 to 9.4 N. Further, pull forces were on average 1.5–2.5 times stronger during lengthy biting events compared to single, brief bites. Maximum lateral pulling forces exerted by 610 g cod were similar to their body weight in air, while 180 g fish were able to pull with a force equivalent to twice their own weight in air. All recorded lateral pull strengths significantly exceeded the known force needed to break single nylon fibres of the netting material. Our results advance understanding of mechanisms and forces involved when cod interact with sea-cage nets and provide important baseline data for the design and production of more bite-resistant netting.     

Invertebrate uptake of lipids in the vicinity of Atlantic salmon (Salmo salar) aquaculture sites in British Columbia

Samples of invertebrates, primary producers, seawater and cores were taken surrounding several aquaculture sites in coastal British Columbia, Canada. Analysis of dissolved organic carbon (DOC) showed a significant decrease (P = 0.027) over 1 km and an overall average of 290 ± 40 μM at 1 m depth. At 10 m, the decrease was not significant and DOC averaged 81 ± 3 μM. The essential fatty acid 22:6ω3 (docosahexaenoic acid, DHA) was significantly lower nearer to the farm sites for all mollusc taxa as well as for mussels alone (P < 0.01). However, mussel wet weight as well as the zooplankton fatty acid marker (ZFA; Σ 20:1ω9, 22:1ω11, 22:1ω9) and 20:1ω9 individually, decreased significantly with distance from the farms (P < 0.03). Principal components analysis showed a similar trend with DHA being higher in molluscs further from the farm. Mussels had significantly higher amounts of DHA compared with other molluscs indicating their potential in multi‐trophic, co‐culturing systems. Bacterial fatty acid markers increased in molluscs with distance from the farms; however, 18:1ω7, which is representative of methane‐oxidizing bacteria, remained higher closer to the farm. In addition, DHA proportions in mussels showed a significant breakpoint at 339 m from the farm suggesting co‐cultured mussels would benefit from placement further than 339 m from farms where DHA would be optimized.     

Transmission of white spot syndrome virus (WSSV) from Dendronereis spp. (Peters) (Nereididae) to penaeid shrimp

Dendronereis spp. (Peters) (Nereididae) is a common polychaete in shrimp ponds built on intertidal land and is natural food for shrimp in traditionally managed ponds in Indonesia. White spot syndrome virus (WSSV), an important viral pathogen of the shrimp, can replicate in this polychaete (Desrina et al. 2013); therefore, it is a potential propagative vector for virus transmission. The major aim of this study was to determine whether WSSV can be transmitted from naturally infected Dendronereis spp. to specific pathogen‐free (SPF) Pacific white shrimp Litopenaeus vannamei (Boone) through feeding. WSSV was detected in naturally infected Dendronereis spp. and Penaeus monodon Fabricius from a traditional shrimp pond, and the positive animals were used in the current experiment. WSSV‐infected Dendronereis spp. and P. monodon in a pond had a point prevalence of 90% and 80%, respectively, as measured by PCR. WSSV was detected in the head, gills, blood and mid‐body of Dendronereis spp. WSSV from naturally infected Dendronereis spp was transmitted to SPF L. vannamei and subsequently from this shrimp to new naïve‐SPF L. vannamei to cause transient infection. Our findings support the contention that Dendronereis spp, upon feeding, can be a source of WSSV infection of shrimp in ponds.     

Beta-glucan: an ideal immunostimulant in aquaculture (a review)

The major hindrance in the development and sustainability of aquaculture industry is the occurrence of various diseases in the farming systems. Today, preventive and management measures are central concern to overcome such outbreak of diseases. Immunostimulants are considered as an effective tool for enhancing immune status of cultured organisms. Among different immunostimulants used in aquaculture practices, β-glucan is one of the promising immunostimulant, which is a homopolysaccharide of glucose molecule linked by the glycoside bond. It forms the major constituents of cell wall of some plants, fungi, bacteria, mushroom, yeast, and seaweeds. Major attention on β-glucan was captivated with the gain in knowledge on its receptors and the mechanism of action. The receptor present inside the animal body recognizes and binds to β-glucan, which in turn renders the animal with high resistance and enhanced immune response. This review highlights β-glucan as an immunostimulant, its effective dosages, and route of administration and furthermore provides an outline on role of β-glucan in enhancing growth, survival, and protection against infectious pathogens pertaining to fishes and shellfishes. Study also summarizes the effect of β-glucan on its receptors, recognition of proteins, immune-related enzymes, immune-related gene expression and their mechanisms of action.     

Shrimp (Litopenaeus vannamei) production and stable isotope dynamics in clear‐water recirculating aquaculture systems versus biofloc systems

Closed recirculating aquaculture systems (RAS) offer advantages over traditional culture methods including enhanced biosecurity, the possibility of indoor, inland culture of marine species year‐round and potential marketing opportunities for fresh, never‐frozen seafood. Questions still remain regarding what type of aquaculture system may be best suited for the closed‐system culture of marine shrimp. In this study, shrimp (Litopenaeus vannamei) were grown in clear‐water RAS and in biofloc‐based systems. Comparisons were made between the system types with respect to water quality, shrimp production and stable isotope dynamics used to determine the biofloc contribution to shrimp nutrition. Ammonia and nitrite concentrations were higher, and shrimp survival was lower in the biofloc systems. Although stable isotope levels indicated that biofloc material may have contributed 28% of the carbon and 59% of the nitrogen in shrimp tissues, this did not correspond with improved shrimp production. Overall, the water column microbial communities in biofloc systems may be more difficult to manage than clear‐water RAS which have external filters to control water quality. Biofloc does seem to offer some nutritional contributions, but exactly how to take advantage of that and ensure improved production remains unclear.     

Resistance of aquaculture net cage materials to biting by Atlantic Cod (Gadus morhua)

Cod bite on aquaculture net cages has resulted in damages like frayed netting and holes, which in part can explain why cultured cod have escaped more frequently than salmon over the last years. We describe damages found on various netting materials subjected to cod bite through field experiments at commercial cod farms. Further, a method to test local cod bite resistance of traditional netting structures is suggested and initial results from a test jig prototype are given. Results from field experiments indicated that cod may have been attracted by types of netting that made it possible to draw filaments out of the twine, while stiff, coated netting structures and thick filaments showed no sign of bite damage during the test period. We concluded that netting materials for cod aquaculture must be resistant to cod bite or be repellent or uninteresting for cod. Based on the present findings, the better choice among the traditional netting materials seemed to be hard-laid netting materials, preferably with a primer that glues the filaments together.     

Economic feasibility of Pabda and stinging catfish culture in recirculating aquaculture systems (RAS) in Bangladesh

Recirculating aquaculture system (RAS) is a unique approach that offers total control to culture a wide variety of aquatic species. As capital investment is higher for setting up RAS, it is necessary to conduct an economic feasibility analysis based on real data. A structured questionnaire was used to collect all economic and technical data on two catfish species, viz., Pabda (Ompok pabda) and Shing (Heteropneustes fossilis), cultured in an RAS farm. The ultimate objective was to estimate net cash flow, net present value (NPV), profitability index (PI), payback period, discounted payback period, internal rate of return (IRR), and sensitivity analysis to find out the best profitability indicators. The analysis revealed that the IRR were 4% and 16% for Pabda and Shing production, respectively. However, for Pabda and Shing productions, the payback periods were 15 years and 4 months and 6 years and 2 months, respectively. The NPV value was positive for Shing production and negative for Pabda. On the other hand, the PI was lower than one for Pabda production and higher than one for Shing production. Therefore, the results showed that the Shing production in the RAS facility could be economically feasible; however, Pabda production may not be viable in RAS due to lower production and longer culture period. This study may suggest that by increasing the production capacity of the farm and market price of the product through the proper supply chain and by decreasing the initial investment, cost of fingerlings and feed, profitability can be achieved in RAS in Bangladesh.

     

Impact of a reduced water salinity on the composition of Vibrio spp. in recirculating aquaculture systems for Pacific white shrimp (Litopenaeus vannamei) and its possible risks for shrimp health and food safety

Tropical shrimp, like Litopenaeus vannamei, in land‐based recirculating aquaculture systems (RAS) are often kept at low water salinities to reduce costs for artificial sea salt and the amount of salty wastewater. Although these shrimp are tolerant against low salinities, innate immunity suppression and changes in the microbial composition in the water can occur. As especially Vibrio spp. are relevant for shrimp health, alterations in the species composition of the Vibrio community were analysed in water from six RAS, run at 15‰ or 30‰. Additionally, pathogenicity factors including pirA/B, VPI, toxR, toxS, vhh, vfh, tdh, trh, flagellin genes and T6SS1/2 of V. parahaemolyticus were analysed. The Vibrio composition differed significantly depending on water salinity. In RAS at 15‰, higher numbers of the potentially pathogenic species V. parahaemolyticus, V. owensii and V. campbellii were detected, and especially in V. parahaemolyticus, various pathogenicity factors were present. A reduced salinity may therefore pose a higher risk of disease outbreaks in shrimp RAS. Because some of the detected pathogenicity factors are relevant for human health, this might also affect food safety. In order to produce healthy shrimp as a safe food for human consumption, maintaining high water salinities seems to be recommendable.     

Tolerance of marron (Cherax Tenuimanus) to hypoxia in relation to aquaculture

Respiration of Cherax tenuimanus (marron) was compared with that of Cherax albidus (yabbie) from measurements in 20 closed system tests (respiration induced oxygen depletion) at ? 25° C. Comparisons were made from the point of inflexion (maximum rate of respiration) of the reversed, asymmetrical, S-shaped oxygen—time curves described by the Richard's equation. Yabbies attained the maximum respiration rate at a lower oxygen concentration (4.0–4.5 mg/l) than marron (5.0–6.0 mg/l). The species did not differ in maximum respiration rate (0.000176 mg/g min^?1) which fell within the range of previous estimates for yabbies. The coefficient for respiratory dependence on body weight was 0.788.A further 25 bioassays on groups of 5 marron were performed at constant, low, oxygen levels and 20°C. The 24-hour LC₅₀ of 7.25% of oxygen saturation approximated the incipient lethal, low oxygen level for marron. The survival time of yabbies for an LC₅₀ of 4.9% oxygen was 45 hours compared with 14 hours for marron.