Proliferative kidney disease in Switzerland: current state of knowledge

This study presents an overview of the distribution of proliferative kidney disease (PKD) in wild and farmed fish in Switzerland based on two sources: (1) the results of routine diagnostic work at the National Fish Disease Laboratory, and (2) the results of a country‐wide survey for PKD. The first case of PKD in Switzerland was diagnosed in 1979 and since 1981, a few cases have been found every year. Affected species were rainbow trout, brown trout and grayling from rivers and fish farms. Most of the diseased fish were found in the lower altitude regions of the country (Swiss midlands). A seasonal distribution of the cases was evident: PKD‐positive fish occurred only from June to November withprominent peaks in August and September. Among infected fish all length classes were present, but the highest numbers of affected fish were found in the length classes <10 cm and 16–20 cm. The evaluation of the samples from a survey of the occurrence of PKD in 2000/2001 revealed a much broader geographical distribution of the infection than expected from routine diagnostic observations. Fish from 56 of 139 rivers analysed by histological examination were positive for parasites. Fish from 131 of these sites were examined macroscopically. Of these, trout from 45 sites showed gross alterations indicative for PKD. Most of the positive fish were found in the Swiss midlands north of the Alps. Fish from six of 65 fish farms investigated were found to be PKD‐positive by histopathological analysis, and in four of these cases fish could be identified as infected on the basis of gross examination.     

Safeguarding the welfare of farmed fish at harvest

Fish welfare at harvest is easily compromised by poor choice of handling and slaughter methods, lack of attention to detail and by unnecessary adherence to fish farming traditions. The harvest process comprises fasting the fish to empty the gut, crowding the fish, gathering and moving the fish using brails, fish pumps, and sometimes also road or boat transport and finally stunning and killing the fish. The harvesting processes commonly used for bass, bream, carp, catfish, cod, eel, halibut, pangasius, salmon, tilapia, trout, tuna and turbot are outlined. These harvesting processes are discussed; the consequences for fish welfare identified and practical tests which can be made at the harvest site highlighted. Welfare at harvest for the majority of farmed fish species can be improved by adopting and adapting existing procedures already known to be beneficial for fish welfare through their use in other fish farming systems or with other species. It is seldom necessary to develop completely new concepts or methods.     

国际虹鳟育种产业简介及其对我国的借鉴意义

虹鳟Oncorhynchus mykiss原产于北美地区,为典型的冷水性鱼类,是世界性重要经济养殖鱼类之一和水产遗传育种领域的重要研究对象。虹鳟是最早采用数量遗传学理论指导遗传选育的水产动物之一,BLUP育种值估计和配合力分析等遗传评定方法以及家系选育、杂交和配套系育种等技术均在虹鳟育种实践中广泛应用。淡水鱼类养殖中,必须使用遗传选育的优良品种的行业共识,最早在虹鳟中确立。目前,在欧洲、北美以及智利等主要鲑鳟鱼养殖国家和地区,虹鳟良种覆盖率均已达到90%以上。鉴于虹鳟仍是我国养殖产量最高的鲑鳟鱼类,其育种工作在许多非原产国都取得了令人瞩目的成就,本文以全球化的视角,从虹鳟养殖与选育的历史概况、虹鳟种业的主要技术手段及产业格局、主要虹鳟育种机构的组织形式与类型特点等方面,简要介绍了国际虹鳟种业的发展及对我国虹鳟种业的借鉴意义。     

Tilapia Lake Virus was not detected in non-tilapine species within tilapia polyculture systems of Bangladesh

Sixteen countries, including Bangladesh, have reported the presence of tilapia lake virus (TiLV), an emerging tilapia pathogen. Fish polyculture is a common farming practice in Bangladesh. Some unusual mortalities reported in species co-cultivated with TiLV-infected tilapia led us to investigate whether any of the co-cultivated species would also test positive for TiLV and whether they were susceptible to TiLV infection under controlled laboratory experiments. Using 183 samples obtained from 15 farms in six districts across Bangladesh, we determined that 20% of the farms tested positive for TiLV in tilapia, while 15 co-cultivated fish species and seven other invertebrates (e.g. insects and crustaceans) considered potential carriers all tested negative. Of the six representative fish species experimentally infected with TiLV, only Nile tilapia showed the typical clinical signs of the disease, with 70% mortality within 12 days. By contrast, four carp species and one catfish species challenged with TiLV showed no signs of TiLV infection. Challenged tilapia were confirmed as TiLV-positive by RT-qPCR, while challenged carp and walking catfish all tested negative. Overall, our field and laboratory findings indicate that species used in polycultures are not susceptible to TiLV. Although current evidence suggests that TiLV is likely host-specific to tilapia, targeted surveillance for TiLV in other fish species in polyculture systems should continue, in order to prepare for a possible future scenario where TiLV mutates and/or adapts to new host(s).     

Proximate and fatty acid composition of 13 important freshwater fish species in central Europe

We aimed to investigate proximate and fatty acid composition of important freshwater fish species in the Czech Republic. Sampled fish include seven species from intensive farming: African catfish, rainbow trout, Wels catfish, Nile tilapia, brook trout, northern whitefish, and pikeperch; eight species from semi-intensive culture systems: common carp, northern pike, pikeperch, grass carp, European perch, tench, silver carp, and catfish; and three species from extensive culture systems: rainbow trout, tench, and common carp. The fat content and fatty acid composition were highly influenced by the culture systems. Simultaneously, we observed a significant dependence of fatty acid composition on the fat content. The content of saturated fatty acids was below 34% in all analyzed fish. Northern pike, pikeperch, and European perch contained with over 50% the highest proportion of polyunsaturated fatty acids. Intensively cultured fish reached the highest content of eicosapentaenoic and docosahexaenoic fatty acid. Nutritional quality was determined by atherogenic and thrombogenic indexes which ranged from 0.27 to 0.63 and 0.20 to 0.61 and by ratios n-3/n-6 (0.54–3.45) and polyunsaturated/saturated fatty acids (0.67–2.01). Results demonstrated that the flesh of all studied species are of high nutritional quality.     

Fish farming of native species in Colombia: current situation and perspectives

In Colombia and the rest of the world, the decrease in capture fisheries production has turned the aquaculture into an alternative source of protein for the populations food security as well as an important productive activity, generating employment and income for the rural communities. The Colombian pisciculture is based on red Tilapia Oreochromis sp. (Linnaeus), Rainbow trout Oncorhynchus mykiss (Walbaum) and cachama blanca Piaractus brachypomus (Cuvier), which currently represent around 96% of the total national production. The remaining 4% comes from other farmed species such as bocachico Prochilodus magdalenae (Steindachner), carp Cyprinus carpio (Linnaeus) and yamúBrycon amazonicus (Spix & Agassiz). From the three main fish species, cachama blanca is the only native species, which has shown excellent performance in pond farming due to its rusticity, omnivorous habits, docility, meat quality, food conversion and disease resistance. The limited offer of Colombian fish farmed species determines its currently low competitiveness and restricted impact on the international markets; thus making necessary to explore the potential of new fish species in order to introduce them to the pisciculture system and to expand the range of fish farming species. A good alternative is the introduction of native catfish, which have great potential for fish farming activity.     

Betaine supplementation enhances the seawater adaptation of salmon, Salmo salar L.

Abstract. The growth of the Atlantic salmon, Salmo salar L., aquaculture industry has been tremendous; from a modest beginning, today's world production of salmon farming is close to 260 million tonnes in ten different countries. In particular the last 20–30 years have seen a dramatic increase in annual sales and production.
The methods vary. From exploiting the natural migrations of this anadromous fish, sea ranching has produced a viable industry. However, controlling the entire life cycle in closed systems has been more successful.
The growth of the farming industry is seriously hampered by such factors as diseases and parasites, algae blooms, environmental pollution, sabotage and rough seas. Several of these factors will not easily be eliminated, although methodical research and development could make the fish farming industry more efficient. Most of the fish farming is situated in remote regions, and the product has to be transported to heavy populated areas for sale, often across borders. The approximate average production costs per kilo differ according to the organization of the industry, average salary, the feed costs and the industrial hurdles, expressed as loss of fish, due to a variety of factors. Even though the market is growing, we must expect fierce competition. Farms producing fish of high quality at low cost will survive. The industry needs healthy fish in well-run farms, smart farmers and a government which helps the industry with reasonable regulations, guidance, applied and basic research, and insight into the future.     

Bioeconomic Analysis of Improved Diets for Lobster,Panulirus ornatus,Culture in Vietnam

Culture‐based growout of tropical spiny lobster, Panulirus ornatus, is a nascent and unique industry that faces a number of challenges and opportunities. Of particular interest to this study is the imminent development of pelleted diets for lobster (probably within 3 yr) that will potentially reduce the industry's dependence on bycatch for feed (with benefits to wild stocks of fish and reduced downstream environmental impacts). The aim of this paper is to conduct a bioeconomic analysis of lobster growout farming in Vietnam and analyze the cost‐effectiveness of potential manufactured feed diets for these farms. Growout lobster farming is found to be a high‐cost and high‐return industry, with a benefit cost ratio of approximately 1.44. Approximately 60% of the total costs are feed related, with the quantity of feed being the production parameter with the highest variability. Hence, reducing the cost and increasing the efficiency of feeding will have a significant impact on the level and variability of profit. It is expected that manufactured diets will improve the profitability by approximately 267 million VND/yr for an individual farmer (15,000 USD) and approximately 435 billion VND/yr for the industry (24 million USD). This is expected to double again if the diets have the added benefit of reducing mortality through the inclusion of vitamins and other additives.     

Microbiological aspects of common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>) and its processing—relevance for final product quality: a review

The aquaculture production of common carp (Cyprinus carpio) is one of the biggest on a global scale, although European production represents a minor part. Thus, common carp is a little-exploited, low-cost, and highly nutritious food source. For development of new quality products that have customers’ appeal and are safe, a combination of traditional and novel technologies can be used. However, good quality raw material is of basic importance for further processing and final product quality. Fish microbiota have a major role in fish spoilage and as potential human pathogens. To diminish the negative impact of the microbiota on fish, different methods and technologies can be used. The important steps before the final product processing in the production of common carp products include purging, transport, pre-slaughter storage, slaughter method, bleeding, cleaning, desliming, descaling, and gutting. The most important factor in fish spoilage prevention is chilling, although to assure longer freshness and shelf-life, the concept of hurdle technology should be used. Many preservation and packaging techniques have been developed for fish products, but not all have been researched for common carp products. This review aims to identify the gaps in research, knowledge, and practice for the microbiological aspects that impact upon the production of high-quality common carp food products.     

Do wild fish species contribute to the transmission of koi herpesvirus to carp in hatchery ponds?

The koi herpesvirus (KHV) has spread worldwide since its discovery in 1998 and causes disease and mortality in koi and common carp populations with a high impact on the carp production industry. Many investigations have been conducted to examine ways of distribution and to identify possible transmission vectors. The answers, however, raise many new questions. In the present study, different wild fish species taken from carp ponds with a history of KHV infection were examined for their susceptibility to the virus. In the tissue of these fish, the virus load was determined and it was tested whether a release of the virus could be induced by stress and the virus then could be transferred to naive carp. Wild fish were gathered from carp ponds during acute outbreaks of virus‐induced mortality in summer and from ponds stocked with carp carrying a latent KHV infection. From these ponds, wild fish were collected during the harvesting process in autumn or spring when the ponds were drained. We found that regardless of season, temperature variation, age and infection status of the carp stock, wild fish from carp ponds and its outlets could be tested positive for the KHV genome using real‐time PCR with a low prevalence and virus load. Furthermore, virus transfer to naive carp was observed after a period of cohabitation. Cyprinid and non‐cyprinid wild fish can therefore be considered as an epidemiological risk for pond carp farms.     

Spatial and temporal variations of sediment quality in and around fish cage farms: A case study of aquaculture in the Seto Inland Sea, Japan

ABSTRACT: Fish cage farming generates large amounts of organic waste in the form of unconsumed feed and fecal matter, resulting in sediment deterioration and a threat to its own sustainability. Field studies analysed the scale of the impact of fish cage farming on sediment quality, variability of impact and spread of sediment enrichment in the vicinity of a fish farm. Two fish culture sites near the Fukuyama area of the Seto Inland Sea of Japan were chosen for the study. There was a significant difference between the quality of the sediment in aquaculture and non-aquaculture areas. The sediment underlying the fish cage farms was found to be extremely reducing, acidic and sulfidic. Sediment ignition loss did not vary markedly with the season. However, the redox potential and acid volatile sulfide content of aquaculture areas did show some seasonal variation. Sediment encircling a 165 m radius from the center of a farm in Yokota was judged as organically enriched by fish farming. A variation in sediment quality within the two sites and also within the stations was observed. Based on sediment quality, the stations could be categorized as less affected, highly affected or moderately affected.     

Economic feasibility of recirculating aquaculture systems in pangasius farming

This study aims to analyze the economic feasibility of recirculating aquaculture systems (RAS) in pangasius farming in Vietnam. The study uses a capital budgeting approach and accounts for uncertainty in key parameters. Stochastic simulation is used to simulate the economic performance of medium and large farms operating with a traditional system or RAS. Data are obtained through structured surveys and a workshop in the Mekong River Delta. Results show that for large farms, net present value increases from an average of 589,000 USD/ha to 916,000 USD/ha after implementing RAS. Overall, the probability that RAS is a profitable investment is found to be 99% for both farm sizes. With RAS, the crucial parameters determining profitability are price, yield, costs of fingerling, feed, and initial investment. Findings on the robustness of the economic performance of RAS are useful to support public and private decision making towards increasing the sustainability of pangasius production.     

Mortality and fish welfare

Mortality has received insufficient attention as a fish welfare topic. Here, we aim to prompt fish farming stakeholders to discuss fish mortalities in relation to welfare. Mortality in farmed fish populations is due to a variety of biotic and abiotic causes, although it is often difficult to differentiate between underlying and immediate causes of mortality. Most mortality appears to occur during episodes associated with disease outbreaks and critical periods (in development or production). Most causes of mortality can be assumed to be associated with suffering prior to death. As mortality rates in farmed fish populations are suspected to rank amongst the highest in commonly farmed vertebrate species, mortality should be a principal fish welfare issue. Long-term mortality rates can be used as a retrospective welfare performance indicator and short-term mortality rates as an operational welfare indicator. Scrutiny of mortality records and determining causes of death will enable action to be taken to avoid further preventable mortality. The welfare performance of fish farms should only be judged on levels of predictable and preventable mortality. Fish farmers will already be monitoring mortality due to commercial and legal requirements. As profitability in fish farming is directly linked to survival, confronting mortality should ultimately benefit both fish and farmers.     

Non‐specific cellular defence mechanisms of rainbow trout (Oncorhynchus mykiss) in intensive and extensive rearing technologies

Water as a habitat is highly variable in terms of the physico‐chemical properties. The aim of the studies was to analyze the quality of the technology by evaluating the non‐specific cellular defence potential of rainbow trout (Oncorhynchus mykiss) in diversified intensity culture systems and in different periods of the breeding cycle. The evaluation was conducted in order to establish the scientific basis for the development of principles for recognition of the culture of this species as ‘organic’. Six rainbow trout rearing farms were selected for the studies and divided into two equal groups according to the production technology: farms with a flow through system (with single water usage – OOH) and facilities with multiple water usage via its backflow (re‐circulating system – RAS). The samples for tests were taken from 20 individuals from each fish farm. In all fish that originated both from OOH‐type farms and RAS operations, an increase in the activity of non‐specific cellular immunity in the autumn was observed. Statistically significant reduction in the activity of cellular defensive mechanisms in small (300–500 g) and big (501–850 g) fish occurred on two 3‐OOH and 3‐RAS farms in spring and autumn in 2011. During these periods, the research has shown the presence of Infectious Pancreatic Necrosis Virus (IPNV), which provoked an immune suppression. Based on the obtained results it is concluded that there were no significant differences in the parameters of non‐specific cellular immunity in rainbow trout originating from different farming systems OOH and RAS.     

鱼类肝脏疾病及防治研究

作者于１９８６￣１９９６年间先后对国内外８个养鱼场的饲养鱼类肝病发生情况作了系统调查，通过体表检查、内脏解剖及肝组织病理观察，对鱼类肝病的症状及病型进行了分级和分类，并讨论了致病原因，提出了防治措施。     

An overview of salmon trout aquaculture in Finland

Abstract

In this case study, we describe the evolution of Finnish salmon trout aquaculture; how salmon trout farming grew as a vital industry, how Finland became the world's leading producer of salmon trout, and how the opening of markets to international competition led to a decline of the industry. The focus is on the continuous interaction between the changing market situation and production decisions. The study reveals the impact of national environmental policy on the competitiveness of the industry. At the moment, the industry is undergoing major structural changes; production has moved to neighbouring countries, and the value chain is concentrated. In future, closer interaction and co‐operation between the actors along the entire fish value chain will be the key factors for success.     

Economic efficiency and optimum stocking densities in fish polyculture: an application of data envelopment analysis (DEA) to Chinese fish farms

Polyculture is commonly practiced in pond aquaculture where several fish species are reared together, creating a multi-output production structure. This study applied a nonparametric data envelopment analysis (DEA) technique for multiple outputs to: (1) measure economic or ‘revenue' efficiency and its technical and allocative components for a sample of Chinese polyculture fish farms; and (2) derive the optimum stocking densities for different fish species. The mean economic efficiency was estimated to be 0.74. Technical inefficiencies accounted for most of the production inefficiencies in Chinese fish farms. On average, farmers should increase grass carp and decrease black carp stocking rates. Smaller farms and those from the developed regions were found to be relatively more technically and economically efficient.     

SOURCES OF PRODUCTIVITY GROWTH IN RAINBOW TROUT AQUACULTURE IN IRAN: TECHNICAL EFFICIENCY CHANGE OR TECHNOLOGICAL PROGRESS?

This study investigates the sources of total factor productivity (TFP) growth in rainbow trout production in Iran using data envelopment analysis (DEA). The Malmquist index is then employed to decompose the TFP growth into technical efficiency change and technological progress. We utilized panel data of 207 trout farms in the country over a 5-year period from 2003 to 2007. The results of this study revealed that TFP growth of rainbow trout farming has an increasing trend over the period at an average annual rate of 3.7%. The trend of cumulative technological change is negative and tends to be contrary to cumulative technical efficiency change. Although there is no technological change or innovation on trout farming, the technical efficiency change was found to be the sole source for TFP change, whereas the mean of technical efficiency was estimated to be about 66%. Therefore, there is still a great relative potential for increasing trout production through improvement in managerial efficiency as well as technological progress. The study suggests that Iran also has considerable room to enhance trout aquaculture's TFP growth by shifting the production frontier with adoption of new technologies and improving innovation.     

Water pollution by Pangasius production in the Mekong Delta,Vietnam: causes and options for control

In this paper, we analyse water pollution caused by farming and processing Pangasianodon hypophthalmus in the Mekong Delta of Vietnam. The results show that 1 tonne of frozen fillets releases 740 kg BOD, 1020 kg COD, 2050 kg TSS, 106 kg nitrogen and 27 kg phosphorus, of which wastewater from fish ponds contributes 60–90% and sludge from fish ponds and wastewater from processing facilities contributes 3–27% of the total emissions. Overall, the combined waste emissions from Pangasius production and processing account for <1% of the total TSS, nitrogen and phosphorus loads in the Mekong Delta. Despite the relatively low contribution to water pollution, further reductions are possible through more efficient use of inputs and low-cost treatment and re-use of effluent streams. The use of cleaner production technologies and the development of wastewater treatment plants could be applied to large farms and processing facilities to reduce water pollution in Pangasius processing. Low-cost options for small-scale farms include the optimization of the discharge design for the re-use of wastewater.     

Economics of fish farming in Saudi Arabia: Analysis of costs of tilapia production

Abstract

Because Saudi Arabia is a substantial importer of fish and its capture fishery is operating beyond maximum sustainable limits, it has a special interest in developing fish farming. It has been encouraging tilapia production. This study examines the costs of tilapia farming in the Central Region of Saudi Arabia using cross sectional data from 23 intensive fish farms. It provides information about the relative importance of different cost items such as variable costs and feed costs in total costs. Also, cost functions are estimated by ordinary least squares and a cubic cost function is found to provide the best fit to the available data. Minimum average cost of production occurs for 201 tonnes of tilapia per year per farm and profit is maximised for a production of 300 tonnes annually per farm. All farms operate at less than profit‐maximising scale and most operate at less than minimum efficient scale. The reasons could be low quality fry, low levels of management expertise in culturing tilapia and the secondary nature of tilapia farming. Lack of water is likely to limit future expansion of tilapia farming in Saudi Arabia.