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Our previous conclusions, that manures may be ineffective in raising aquaculture yields above levels attained by daily N and P fertilization, is limited to conditions of soil and water naturally rich in nutrient minerals and carbonates. Manures may be valuable inputs when soil and water are poor in essential nutrients, or of a low pH. Situations exist in which manures are the cheapest source of N and P minerals.

Reducing dependency on environmentally unsustainable formulated feeds, most of which include limited reserves of fishmeal as a protein source, is a priority for the aquaculture industry, particularly for intensive culture systems. One approach is to increase nitrogen reuse within the system by feeding nitrogen-rich aquaculture effluent to deposit feeders, thereby closing the aquaculture nitrogen-loop. This study, for the first time and on a laboratory-scale, has reared juveniles of the sea cucumber Holothuria scabra at high densities solely on particulate organic waste from a commercial-scale land-based abalone recirculating aquaculture system. Furthermore, growth rates and biomass yields were increased significantly by adjusting the effluent C:N from 5:1 to 20:1 by adding exogenous organic carbon sources (glucose, starch and cellulose), so fuelling accelerated heterotrophic bacterial production within the redox-stratified tank sediment. Sea cucumber juveniles reared solely on effluent had a biomass density of 711 g m−2 after four months whereas animals reared on starch-amended effluent (the best performing treatment) had a final density of 1011 g m−2. Further optimisation of this approach could increase biomass yields and pave the way for the commercial cultivation of deposit feeding animals on waste streams, thus contributing to more environmentally sustainable aquaculture. Here, the nitrogen that originated from fishmeal is not lost through the discharge of aquaculture effluent; rather, it is immobilised into single cell biomass that is up-cycled into high-value secondary biomass. We demonstrate that sea cucumbers can be produced at high density through the manipulation of the C:N ratio of aquaculture effluent.

Biofouling causes major functional and economic problems for aquaculture due to their settlement and subsequent growth on fish-cage netting. As biofouling management is an economic and environmental issue, feasible management practices are clearly required to balance industries and environmental requirements. The most frequent way to control biofouling in aquaculture is by applying Cu-based antifouling paints on fish nets to prevent the undesired growth of biofouling. The most important fish species employed in marine fish farming are cultivated with knotted nylon and ultra-high-molecular-weight polyethylene (UW-polyethylene) nettings. In this study, we examined the effects of two commercial Cu coatings and two manufactured net materials (nylon and UW-polyethylene) on biofouling biomass, community structure, Cu bioaccumulation and the metal composition of fouling assemblages in order to provide farmers with a tool to help reduce the environmental impact of the biocide employed for coating nets. The MDS ordination of the samples coated with both paints on nylon and UW-polyethylene nets showed a gradual modification of community structure associated with rising Cu concentrations. The PCA analysis indicated that the ordination of trace element composition of biofouling varied between concentrations and nets in both paints. The experiments revealed that the fouling biomass decreased following negative exponential regression with an increasing Cu concentration. The increase in fouling biomass with reduced Cu bioaccumulation was greater in nylon than in UW-polyethylene nets. In the nylon nets, the median bioaccumulation on nets (CuF-50) rose with an 0.75- to 0.82-fold increase in the basal biomass. Conversely, biomass increased 0.50- to 0.63-fold the basal or minimum fouling biomass with a full antifouling paint concentration (B0) when CuF-50was calculated in the UW-polyethylene nets. These results suggest that similar reductions in bioaccumulated Cu in both nets could be achieved without sacrificing excessive fouling biomass increases.

Minimizing ammonium is one of the most important concerns in the practice of aquaculture. Chemoautotrophic bacterial nitrification (CBN) and heterotrophic bacterial assimilation (HBA) are the two main ammonium pathways in aquaculture water under light-limited conditions. CBN oxidizes ammonia–nitrogen (NH4+-N) to nitrite–nitrogen (NO2−-N) and finally to nitrate–nitrogen (NO3−-N), and this is the primary strategy employed in recirculating aquaculture systems using fixed-cell bioreactors. Zero-exchange management systems based on HBA and biofloc technology have been developed referred as biofloc aquaculture systems. HBA is encouraged in biofloc aquaculture systems by increasing the C/N ratio. However, NO3−-N build-up was found in many studies examining these systems, with CBN proposed as the responsible mechanism and documenting the factors leading to the occurrence of the CBN process. This paper examines the relative importance of CBN and HBA in biofloc aquaculture systems. A mechanism is proposed and future study aimed at mediating NH4+-N pathways in biofloc aquaculture systems is recommended.

Biofouling causes a range of problems in aquaculture, and there is a need to validate the effectiveness of antifouling products marketed in the industry. We tested the antifouling performance of four commercial aquaculture netting options at a trout aquaculture operation in the Bras d'Or Lakes, Nova Scotia, Canada. This site has brackish water and a severe mussel (Mytilus edulis) biofouling problem – complete net occlusion can occur within four weeks of the onset of mussel larvae settlement. We tested white and black nylon netting as controls, and four products marketed as having non-toxic antifouling properties: white and black Finsulate®, white Netminder® coating on white nylon netting, and white Dyneema® netting. In 2017, using image analysis measurements of fouling, we found only Netminder® significantly delayed fouling by two weeks over controls. Nonetheless, biofouling on all netting treatments (a mixture of filamentous algae and mussels) reached saturation (i.e. complete net occlusion in the images) within six weeks. After 17 weeks, the Netminder® coated netting supported significantly greater mussel biomass (measured by shell masses). In 2018, a follow-up experiment found that Netminder® caused a one-week delay in exclusively mussel biofouling compared to the white nylon control netting. We conclude that none of the options tested are likely to reduce severe mussel biofouling substantially. However, the benefits of a one-to-two week delay in biofouling caused by Netminder® (including reduced cleaning costs and diminished influence of mussels on water properties and the benthos under the net pens) should be weighed against the cost of application and maintenance for the coating.

The integration of bioremediation systems is one of the most promising techniques to mitigate the environmental impact of aquaculture effluents. Also, it allows nutrient recycling, production diversification, and the creation of high-value by-products. In marine aquaculture, where the implementation of salt-tolerant extractive species is essential, halophyte plants have demonstrated to be optimal candidates for bioremediation of saline aquaculture wastewater. This study aimed to evaluate for the first time the efficiency of Sarcocornia neei (Lag.), a halophyte plant with high adaptability, salinity tolerance and growth potential when irrigated with seawater, in removing nutrients from marine fish aquaculture wastewater and artificial effluents. Two experiments were carried out. In the first one, the growth rate, removal of inorganic nutrients, and accumulation of organic compounds in deep-water hydroponics and sand-substrate systems were evaluated in artificial effluents with different nitrogen and phosphate loads during 70 days. In the second, due to the better performance achieved by S. neei in deep-water systems, its nitrogen removal efficiency and productivity rates were evaluated in deep-water aquaponics with marine aquaculture wastewater and artificial effluents at higher nitrogen loads during 61 days. The highest productivity rates achieved by S. neei (14.41 ± 0.78 kg m−2) were obtained in deep-water culture units, reaching 100% plant survival, suggesting that this species is more suitable for its implementation in this type of system. Significant total ammonia nitrogen removal rates were obtained by the plants, achieving a maximum in sand-substrate systems (0.68 ± 0.41 g m−2 day−1). The results of nitrate removal rates obtained by S. neei (11.25 ± 31.38 g m−2 day−1) make this species an ideal potential candidate for the removal of this compound present in marine RAS effluents. Accumulation of organic compounds was corroborated by obtaining a significant increase (p These results indicated that S. neei is a good candidate for its use as a biofilter for marine aquaculture wastewater. Further investigations should be done to analyze possible influences on growth rates and nutrient removal efficiency by adding essential micronutrients, adjusting effluent salinity, and implementing different plant densities. Also, further studies could be interesting to determine the feasibility of long-term integration of a bioremediation system with S. neei associated with marine aquaculture effluents, approaching its application to industrial-scale production systems.

The oxygen demand, acidification potential, and waste loads of carbon dioxide, nitrogen, and phosphorus from feed were determined for production of channel catfish Ictalurus punctatus, tilapia Oreochromis spp., Atlantic salmon Salmo salar, rainbow trout Oncorhynchus mykiss, and whiteleg shrimp Litopenaeus vannamei. Loads of these variables in culture systems (system loads) at typical FCRs ranged from 1090 to 1500 kg t− 1 for feed oxygen demand, 270–440 kg t− 1 for acidification potential, 1186–1885 kg t− 1 for carbon dioxide, 35.9–63.5 kg t− 1 for nitrogen, and 6.1–15.9 kg t− 1 for phosphorus. Using these estimates as representative of feed-based aquaculture and literature data on the proportions of system waste loads typically discharged to the environment (environmental loads), the approximate amounts of waste generated globally by feed-based aquaculture were estimated to be small in comparison to estimates of global anthropogenic waste. Nevertheless, aquaculture should lessen its environmental waste load, and the benefit of improving FCR in reducing waste load was illustrated. Statement of relevance This research will be important in efforts to assess the pollution potential of aquaculture facilities. This will be especially important for aquaculture certification efforts.

Cost of effluent treatment, water quality maintenance and feeds constitute most of aquaculture's operational costs, and influence its sustainability. The present study examined the effectiveness of periphyton for biofiltration of mariculture effluents. Marine periphyton was allowed to spontaneously develop on a plastic net substrate, in experimental bioreactors that were fed with effluents from fish mariculture ponds. Biomass development and nutrient uptake were followed over four seasons. Attention was given to the orientation and area of the net substrate, season and additional operational factors. The highest specific growth rate (SGR) of 27% day− 1 was measured during the second week of periphyton growth in the summer. Mean daily periphyton production rates in the spring and autumn were 2.4 and 1.8 g (ash-free dry weight) m− 2 day− 1, respectively. The vertical orientation of the net substrate was overall advantageous over the horizontal orientation. Increasing the substrate area of vertically oriented nets in the biofilter increased the removal efficiency of total ammonia nitrogen (TAN) up to 80%, and allowed more biomass production in the biofilter. Multiple polynomial regression models suggest strong effect of biomass weight and effluent retention time on the removal efficiency of TAN and dissolved inorganic nitrogen (DIN). The removal rates of TAN and DIN in these experiments were between 0.11 and 1.2 g N m− 2 (substrate area) day− 1 for periphyton at the age of 7 and 42 days, respectively. Marine periphyton seems to be a simple, low cost and sustainable component, which can perform biofiltration/rehabilitation of water quality and potentially serve as feed for fish and shrimp.

The development of microalgae culture technology has been an integral part of the production of commercially important species in aquaculture. This has been the reason to make great efforts in order to understand several aspects of the microalgae production. The detailed research on monitoring cell growth, which is considered a fundamental part for the use of microalgae in aquaculture, has been, however, overlooked. In this paper, a calibration curve is proposed; correlating the specific absorbance and measured cell density by cell counting (cells mL − 1 ), from four microalgae species important for aquaculture. The final result allows the prediction of cell counting from absorbance using cells mL − 1 = β 1 2 − 4 β 2 β 0 − Abs 1 2 − β 1 / 2 β 2 which is valid for Abs β 0 − β 1 2 /(4 β 2 ). The adjusted determination coefficients ( r 2 adj ) were 0.998, 0.995, 0.991, and 0.998 for Chaetoceros calcitrans , Isochrysis affinis galbana (T-Iso), Nannochloropsis gaditana and Phaeodactylum tricornutum , respectively. The results showed that the obtained equations can be used with an error of less than 5% for microalgae densities of up to 1.01 × 10 7 cells mL − 1 , 2.11 × 10 7 cells mL − 1 , 8.52 × 10 7 cells mL − 1 , and 1.67 × 10 7 cells mL − 1 in the abovementioned species, respectively. Statement of relevance A rapid, simple and specific spectrophotometric methodology for biomass measurements of four microalgae species with high importance in aquaculture was developed. The specific wavelength for the maximum absorbance was established for each of the studied species. With the methodology described here, the harvest time will be easier to identify in facilities where these algae are cultured, and can be also easily tested in other monocultures. In addition, a predictive model was satisfactory and useful for a wide range of cell densities yielding a methodology with high potential for automation. A useful tool was developed for cell counting of microalgae in aquaculture.

A high-rate nitrogen removal process is required to maintain the water quality in aquaculture tanks used to produce high-density fish populations in recirculating aquaculture systems. In this study, a combined pilot-scale system of down-flow hanging sponge (DHS) reactors and upflow sludge blanket (USB) reactors was applied as a nitrogen removal system for a longtooth grouper Epinephelus bruneus recirculating aquaculture system. The DHS reactors demonstrated high total ammonium nitrogen (TAN) removal efficiencies and the TAN concentration in the aquaculture tank was maintained at 0.32 ± 0.12 mg-N·L−1. The USB reactor fed with sodium acetate acted as a denitrification unit and adjusted the pH through denitrification reaction. All E. bruneus survived the entire experimental period and the daily weight gain rate of 0.6%·day−1 was comparable to that in marine aquaculture. This result shows that the DHS-USB system to be a novel applicable system for nitrogen removal processes in recirculating aquaculture systems and further study at a large scale should be recommended.

Nitrate is typically removed from aquaculture effluents using heterotrophic denitrification reactors. Heterotrophic denitrification reactors, however, require a constant input of readily available organic carbon (C) sources which limits their application in many aquaculture systems for practical and/or economic reasons. A potential alternative technology for removing nitrate currently applied for treating surface and drainage water is based on using wood by-products as a carbon source for denitrification. Using lab-scale horizontal-flow woodchip filters, the current study investigated the potential of optimizing woodchip reactors for treating aquaculture effluent. A central composite design (CCD) was applied to assess the effects of simultaneously changing the empty bed contact time (EBCTs of 5.0–15.0 h; corresponding to theoretical hydraulic retention times of 3.3–9.9 h) and bicarbonate (HCO 3 − ) inlet concentration (0.50–1.59 g HCO 3 − /l) on the removal rate of NO 3 − N, and additional organic and inorganic nutrients, in effluent deriving from an experimental recirculating aquaculture system (RAS). Volumetric NO 3 − N removal rates ranged from 5.20 ± 0.02 to 8.96 ± 0.19 g/m 3 /day and were enhanced by adding bicarbonate, suggesting that parts of the removal was due to autotrophic denitrification. The highest N removal rate (8.96 ± 0.05 g/m 3 /day) was achieved at an EBCT and HCO 3 − combination of 15 h and 1.59 g HCO 3 − /l. Bicarbonate inlet concentration as a single factor had the strongest effect on N removal rates followed by the interaction with EBCT, and EBCT 2 (quadratic term). The study thus indicates that woodchip beds may be applied and optimized for removing nitrate from aquaculture effluents. Statement of relevance This study is a relevant contribution to research in aquaculture as it presents an alternative method for removing nitrates from aquaculture effluents especially for less intensive fish farms. Furthermore, it shows how this method can be optimized to yield higher removal rates of nitrate.

Environmentally responsible disposal of solid organic wastes from land-based brackish and marine recirculating aquaculture systems is critical for promoting widespread acceptance and implementation, but conversion efficiency of saline sludge to biomethane is generally low. We describe the development of a microbial consortium that can convert marine organic fish waste solids to biomethane at over 90% efficiency. The halotolerant microbial consortium, which was developed by sequential transfer in seawater with fish waste, is optimized for low COD:N ratios typical of organic fish waste and does not require addition of amendments such as organic carbon or nutrients. Temperatures for maximum rates of conversion range from 26 to 35 °C. Five predominant phylotypes identified in the microbial consortium by denaturing HPLC were isolated. Two isolates included anaerobic fermentative bacteria identified as a strain of Dethiosulfovibrio and a strain closely related to Fusobacterium spp., which both hydrolyze and ferment proteins, peptides and amino acids. The other three isolates included an acetate-utilizing methanogenic archaeon identified as a strain of Methanosarcina and two hydrogen-utilizing methanogenic archaea identified as strains of Methanogenium and Methanoplanus . Bioconversion rates of sterile fish waste with the reconstituted microbial consortium containing all five isolates were equivalent to rates observed with the original enriched consortium after one sequential transfer. The results demonstrate unequivocally that halotolerant consortia of bacteria and archaea can be developed for bioconversion of saline organic solid waste with high efficiencies equivalent to those attained with non-saline waste systems. Understanding the microbial community composition is critical for management of solid organic waste from land-based marine aquaculture systems and to maintain or restore microbiota during start up and throughout the production process. Statement of relevance Appropriate disposal of solid organic wastes from land-based brackish and marine recirculating aquaculture systems is critical for promoting widespread acceptance and implementation. We demonstrate that halotolerant consortia of bacteria and archaea can be developed for bioconversion of saline fish waste with high efficiencies equivalent to those attained with non-saline waste systems.

Marine pollution from aquaculture wastewater is a widespread and increasing ecological problem. Algae, with their ability to remove surplus nutrients from wastewater, are a good tool for achieving more sustainable aquaculture. In this study, the capability of different biomasses of Chaetomorpha linum and Cladophora prolifera for the bioremediation of nutrient-rich (ammonium, nitrate and phosphate) seawater was compared. The results suggest that 10 g L−1C. linum is an excellent candidate for aquaculture wastewater bioremediation. However, the bioremediation efficiency of C. linum was significantly affected by seasonality, with the greatest performance in nutrient removal exhibited by algae harvested in summer. C. linum harvested in winter and acclimated to lab conditions for two months, significantly improved the removal efficiency of both ammonium and nitrate, while worsening that of phosphate. Irrespective of season and acclimation, the simultaneous presence of ammonium and nitrate in seawater strongly inhibited nitrate removal. Thus, we propose the use of a two-step system, tested at the laboratory scale, in which nutrient-enriched seawater can pass through two different algal ponds. C. linum was able to achieve almost complete removal of ammonium in 24 h in the first step, while the second step improved both nitrate and phosphate removal efficiency. The two-step system is an effective innovation for the use of algae in bioremediation of aquaculture wastewaters.

Disease outbreaks are a major concern in aquaculture. This is particularly true in intensive recirculating aquaculture systems (RASs), due to the high rearing densities in a system where high concentrations of organic matter are produced with minimal water exchange. This study assessed the survivability of the common fish pathogen Streptococcus iniae in a solid-removal unit of a RAS, the upflow anaerobic sludge blanket (UASB). A PCR detection method, along with an improved protocol for the extraction of high-quality DNA from sludge samples, were utilized for this purpose. This method enabled detection of S. iniae at a minimum concentration of 7.6 × 10 5 CFU mL − 1 raw sludge. We examined the survivability of S. iniae in batch digesters, which consisted of sealed serum bottles filled with sludge from the UASB reactor, and in laboratory-scale flow-through UASB reactors that were continuously fed with fish waste sludge. Results demonstrated a gradual decrease in the intensity of the PCR-amplified product to the point of no detection in either batch or UASB digesters, suggesting that the conditions present in the UASB reactor are not favorable for S. iniae . The PCR-based detection method was successfully applied to sludge from a commercial RAS enabling detection of potentially pathogenic bacteria. Statement of relevance The manuscript addresses the control of bacterial disease-causing agent in a near-zero discharge aquaculture system which contains a novel solid removal unit. The bacteria studied is S. iniae , a significant disease-causing agent in aquaculture. The potential threat of disease outbreaks increases with the intensification of the culture system, such as the one described and analyzed in this study. This intensification is of high relevance to the industry, as it reduces environmental contamination due to fish production as well as enables fish culture in places distant from a natural water source.

The aquaculture industry needs a stable supply of feed resource materials in sufficient quantities and quality for future growth, in particular the fatty acids eicosapentaenoic acid (dha) and docosahexanoic acid (DHA) which so far have been ensured by inclusion of fish oil. About 70% of the available fish oil is being used in aquafeeds, but the global supply of fish oil is limited and emerging omega-3 markets are competing with the aquaculture industry for this valuable resource. New sources of dha and DHA must be fully developed to cover the global demand, and marine microalgae are regarded as a promising alternative as the primary producer of all the EPA and DHA in marine food webs. Industrial cultivation of phototrophic microalgae is conducted in open pond systems or closed photobioreactor systems, designed to maximize the utilization of light energy and to achieve efficient uptake of nutrients and CO 2 . The economics of microalgae production heavily depend on the photosynthetic productivity, and there are ongoing efforts to increase the microalgae productivity following different strategies. The first is to exploit the cultivation conditions to direct the metabolism towards lipid production. The second is to improve biomass productivity or lipid yield by mutagenesis and selective breeding, and the third strategy is to improve strains by genetic modifications to optimize light absorption and increase the biosynthesis of EPA and DHA. The inclusion of whole microalgae cells in aquafeeds will require sufficient processing to ensure maximum nutritional uptake, involving dewatering and cell disruption in order to maximize the bioavailability of nutrients. The roadmap of microalgae to become a sustainable aquafeed resource must include interdisciplinary research and development efforts along the whole value chain to achieve biomass production in an industrial scale. A techno-economic analysis of microalgae production was conducted based on biological and technical parameters from the literature under various scenarios, showing that biological productivity, geographical locations and production technology are important factors to lower production cost. The production cost of EPA and DHA equivalents revealed the lowest cost for flat panel photobioreactors in locations with clear sky conditions. Sensitivity analysis showed that optimizing photosynthetic efficiency and doubling of the EPA and DHA yield could reduce the cost to 11.9 USD per kg of total EPA and DHA equivalents. Our findings suggest that focused research efforts can contribute to achieve economically sustainable production of microalgae rich in EPA and DHA for use in aquafeed in the near future.

The rapid removal of suspended solids from aquacultural systems is of utmost importance in maintaining healthy stock and system stability and in addressing environmental concerns. This research tested a new approach, successfully manipulating fecal density to the point of floatation. Fecal casts floating at the water's surface can be transported quickly to a removal device. The speed of removal minimizes opportunity for leaching, and exposure to shear forces and turbulence caused by mechanical devices and fish motion. Waste thereby persists as larger particles, which are easier to remove by traditional microscreens or skimming apparatus. Four different low-density feed additives were tested in different dosages and gradings on duplicate groups of rainbow trout, in order to appraise the effects on fecal density, and on growth and health of fish stock. The control groups received the same basal diet without additives, which resulted in fecal densities in the upper ranges expected for commercial trout diets at 1.04 g cm − 3 and 1.05 g cm − 3 for water-soaked and intestinal feces, respectively. Five of the additive diets significantly reduced the density of both intestinal and water-soaked feces, with the most effective (cork; 0.5–1 mm; 2%) leading to floating feces (4.39% to 1.00 g cm − 3 and 5.12% to 0.98 g cm − 3 for intestinal and water-soaked feces, respectively). The larger grade of cork granules performed significantly better than the smaller grade. The possibilities for reducing levels of effective cork incorporation and enhancing effects on density by other quality improvements are discussed. Feed efficiency and fish health were not impaired by the additives. It is suggested that the systematic manipulation of fecal density with low-density additives may achieve economic and ecological advances and offer a new and effective means of managing and optimizing waste output from aquaculture. The effects of floating feces on removal efficiency, leaching effects, water quality and operating costs in aquacultural systems have to be further explored.

Bivalve aquaculture currently utilizes two main farming practices: intertidal (beach) and deep-water (suspended) culture. Although suspended culture offers a number of advantages during both nursery and grow-out phases, two commonly encountered issues – shell deformities and biofouling – lead to reduced seed and final product quality in some species and preclude other species from being cultured in suspension. None of the existing strategies for controlling these issues is efficient and fully reliable. In this study we tested the efficiency of two new methods for controlling biofouling and shell deformities in suspended culture of bivalves using basket cockle Clinocardium nuttallii as a model species. The first method involved a short-term increase in bivalve stocking density during peak plankton concentrations and biofouling settlement periods. The second method comprised adding artificial growth medium (expanded clay aggregate) to culture enclosures. Both high-density and growth medium treatments significantly reduced the incidence of C. nuttallii shell deformities compared to the control treatment (by 86 and 72%, respectively). This finding suggests that clam shell deformities in suspended culture primarily develop due to the lack of structural support normally offered by the substratum. Both treatments also significantly reduced barnacle fouling rate (by 67 and 83%, respectively). Additionally, growth medium treatment led to a significant reduction in tube worm fouling, as well as combined fouling rate and intensity, but it was less effective in controlling sponge fouling. Overall, both high-density and growth medium treatments showed promise in reducing the incidence of shell deformities and the amount of biofouling on C. nuttallii in suspended culture. These treatments are inexpensive, environmentally-friendly, readily available to shellfish growers, and may be further refined and adapted for a variety of cultured bivalve species. They have the potential to improve the efficiency of suspended grow-out systems and extend the option of suspended culture to bivalve species currently grown on the beach only.

In order to compare the efficacy of seaweeds and bacterial biofilm for removing nitrogenous wastes from recirculating marine aquaculture, Ulva lactuca L., Undaria pinnatifida Suringar, and a trickling biofilm filter were introduced to systems housing Haliotis iris Gmelin. Experiments were triplicated and run for 14 days. Although biofilm filtration maintained ammonium at low concentrations (around 0.10 mg l − 1 ), nitrate levels increased linearly over time, reaching 2.30 mg l − 1 . Seaweeds maintained ammonium at concentrations that were consistently lower (around 0.03 mg l − 1 ) than those observed with biofilm filtration. Moreover, nitrates were undetectable and pH less variable, whilst valuable seaweed biomass, with increases up to 50%, was generated. Seaweed filtration thus has the potential to improve the efficiency and productivity of recirculating aquaculture, via enhanced culture conditions and the production of economically valuable biomass.

The safety of electrolyzed seawater was evaluated by measuring the production rate of organic halogen compounds and the occurrence of reverse mutations. Aquaculture feedwater and wastewater were collected from a fish-culturing facility, and available chlorine of approximately 1.0 mg/L was generated to ensure a disinfectant effect. More than 90% of the generated organic halogen compounds were bromoform. The amount of bromoform was far less than the reference values for drinking water standards in Japan and the U.S., provided that the electrolyzation was performed within the range of normal use. The reverse mutation assay of electrolyzed seawater showed no mutagenicity. Electrolyzed seawater with available chlorine at an adequate level for disinfection can be used safely and effectively in various aspects of aquaculture.

Biofiltration allows for environmentally sustainable mariculture. An intensive, biofiltered recirculating integrated system producing fish and seaweed on a semi-commercial scale was evaluated with respect to production and to nutrient and heat budgets. The system consisted of abalone (Haliotis discus hannai) and sea urchin (Paracentrotus lividus) tanks, an intensive fishpond (Sparus aurata), and a three-stage Ulva lactuca biofilter, which cleaned and recirculated 50% of the effluent back to the fishpond. To preserve water heat, the shellfish and fishpond units were both covered with greenhouses; the biofilter unit was covered with a greenhouse only during winter. Seaweed yield was variable and averaged 94 and 117 g m−2 day−1 (fresh weight) in periods with and without greenhouse cover, respectively. Protein content of U. lactuca averaged above 34% of dry weight. The biofiltration of only 50% of the water through the seaweed biofilter reduced the export of dissolved nutrients to the environment by nearly 30%. Peak ammonia excretion by the morning-fed fish coincided with maximum seaweed light-dependent ammonia uptake and concentrations of ammonia in the fishpond remained within nontoxic limits. Also, daytime photosynthesis of U. lactuca (uptake of CO2) met fish respiration (production of CO2), thus balancing fishpond pH levels within safe limits regarding ammonia toxicity. Daytime oxygen demand by the fish was partially met by the photosynthetically generated oxygen. Before covering the biofilter with a greenhouse, it lost much heat, reducing the temperature in the fishpond. Following the greenhouse covering of the biofilter, heat loss ceased and consequently the fishpond temperature was raised. Recirculation through the biofilter improved system sustainability; it reduced water use, lowered negative environmental impact, and maintained stable and safe water quality conditions in the fishpond.

This note summarizes a review by Hindar et al. (1991) outlining the genetic consequences of aquaculture on natural fish populations. Publication of the full paper (Hindar et al., 1991) has preceded that of the present volume; this note is included to permitt a more complete presentation of the papers read at the Loen symposium on interactions between cultured and wild Atlantic salmon ( Salmo salar ).

The water-quality characteristics of a new system for the integrated culture of fish ( Sparus aurata L.) and seaweed ( Ulva lactuca L.) were examined. Seawater was recirculated between intensive fishponds and seaweed ponds. The seaweed removed most of the ammonia excreted by the fish and oxygenated the water. A model consisting of several tanks and a pilot consisting of two 100-m 3 , 100-m 2 ponds were studied. In both, the metabolically dependent water-quality parameters (dissolved oxygen, NH 4 + -N, oxidized-N, pH and phosphate) remained stable and within safe limits for the fish during over 2 years of operation. The design allowed significant increases in overall water residence time (4.9 days), compared with conventional intensive ponds, and produced a high yield of seaweed in addition to the fish. The design provides a practical solution to major management and environmental problems of land-based mariculture.

A bench-scale fluidised bed bioreactor was used to treat aquaculture effluent intended for recycling. The reactor was loaded with ammonia-nitrogen (NH 4 -N) from 0.025 to 5.675 g m −2 day −1 . Maximum NH 4 -N removal was 82% of influent concentration when loading was between 0.201 and 0.397 g m −2 day −1 ; at this level, effluent NH 4 -N did not exceed 0.05 mg 1 −1 .

The fate of orally administered oxytetracycline in a fresh-water hatchery was investigated using high-performance liquid chromatography. A filter of nominal porosity 50 μm in the farm effluent was capable of at least a 500–650-fold concentration of the oxytetracycline into the filter retentate flow. No oxytetracycline was detected in the filtered farm effluent (limit of detection 0.02 μg·ml−1). Analysis of hourly samples of the retentate taken over a 24-hour period allowed an estimate of the daily amount of oxytetracycline retained by the filter. This estimate (1250 g) was of the same order as the amount of oxytetracycline used on the farm (904 g on the day of sampling and 1104 g on the preceding day). Thus the quasi-totality of the input oxytetracycline was removed from the farm effluent by the filter. A sedimentation trap on the filter retentate flow removed oxytetracycline from this flow at a variable and lower (12–92%) efficiency. It is argued that correct design of effluent treatment systems could significantly reduce the environmental impact of land-based fish farms.

In recent years aquaculture has gained importance as a source of various products in the world market. Because feed costs form largest portion of production costs, research continues to focus on artificial diet production using simple, available, inexpensive feed ingredients and feed-manufacturing technologies. The present study was designed to identify which critical operations influenced pellet water stability and usable milling pellet recovery. A quality engineering design was adopted to check the effect of five variables at two levels: binding ingredient (wheat/potato flour), residence time in powder and wet mixing (10–15 min), thermal pretreatment (with/without steam, 90°C, 10 min) and drying temperature ( 60 80 °C ). Critical parameters found were drying temperature, thermal pretreatment and binding ingredient-drying temperature interaction. Process analysis helped to obtain a competitive product with technological advantages.

Nitrification by biological filters in closed-system aquaculture is the primary method for removing ammonia from the culture water. This paper examines experimentally the process of selective ion exchange as an alternative to biological oxidation of ammonia. We propose that an inexpensive ion exchange column would be useful as a backup system to the microbiological filters, or as an alternate system used while treating diseased animals in culture so as not to harm the nitrifying bacteria of the main biological filters.

Fibrillated polypropylene film, dyed with carbon black, was found to attract and retain more mussel larvae than coir, sisal, or polypropylene film of other colours. At the same time it was unattractive to barnacles, tunicates and other competitors. Pieces of the film, inserted into the lay of a rope manufactured out of the same material, appear to provide the best commercial prospects.

Future increases in electric power requirements will provide greater opportunities to use waste heat from electric generating stations for beneficial purposes. Thermal effluents can be used as a source of warm water which may be utilized to control and maintain a fish-farm system within optimum thermal limits. High temperatures of thermal effluents will exert their primary effect on cultured organisms through increased activity and metabolism. Site studies in thermal effluents indicate that the principal fishes attracted to thermal effluent areas are warmwater species and that these fish could provide suitable culture animals. At present, few fish species are cultured in thermal effluents under controlled conditions.

A portable ‘Tyndalometer’ is described for measuring the concentration of algae in aquaculture tanks. This simple, inexpensive, robust, battery-operated device can be readily constructed from common materials. It uses a photoresistor to measure the transmittance of light, and has been tested with two species of unicellular alge, at a great range of concentrations.

A supplementary feed containing 30% coffee pulp was evaluated for use in the culture of Tilapia aurea in El Salvador, Central America. A comparison of the coffee pulp feed with a feed containing all of the same ingredients except coffee pulp was made with T. aurea raised in 1.0-m 3 cages suspended in a fertilized earthen pond. Survival was high in all treatments and there was no significant difference in average weight gain between groups of fish receiving the two experimental feeds. Production trials were conducted in 100-m 2 fish pens and in 0.05-ha earthen ponds. Pen-raised fish receiving coffee pulp feed grew faster throughout the experiment, and total production was approximately twice that in control treatments. Highest production in pens was 1.25 kg/m 2 per year. Results of production pond trials using T. aurea at 9 000/ha and stocked with the piscivorous Cichlasoma managuense yielded an estimated 3 392 kg/ha per year in fed treatments and 2 049 kg/ha per year in controls. Low feed conversion (1.92) and low feed cost resulted in an increase in net annual earnings of $251.00/ha.

Dehydration and clearing by 2,2-dimethoxypropane (DMP) is completed in 30 min. Tissues of eel and oysters, both of importance for aquaculture purposes, were used in a comparison of the DMP procedure and conventional dehydration-clearing. We found that the cutting quality and the histological appearance of the tissues were quite similar. The time-saving aspects are considered as an advantage of DMP for rapid results in aquaculture research.

A combined tertiary sewage treatment—marine aquaculture system has been developed, tested and evaluated using several different experimental sizes and configurations located both at Woods Hole, Mass. and Fort Pierce, Fla. Domestic wastewater effluent from secondary sewage treatment, mixed with sea water, is used as a source of nutrients for growing unicellular marine algae and the algae, in turn, are fed to oysters, clams, and other bivalve molluscs. Solid wastes from the shellfish are fed upon by polychaete worms, amphipods, and other small invertebrates that serve as food for flounder, lobsters, and other commercially valuable secondary crops. Dissolved wastes excreted by the shellfish and other animals and any nutrients not initially removed by the univellular algae are removed by various species of commercial red seaweeds (Chondrus, Gracilaria, Agardhiella, Hypnea) as a final ‘polishing’ step. The final effluent from the system is virtually free of inorganic nitrogen and is incapable of supporting further growth of marine life or of contributing to eutrophication of the receiving waters. A description of experiments with the above food chains and preliminary results with some alternative approaches are discussed, including a detailed account of the nitrogen mass balance through all of the components of one of the experimental systems.

Toxic dioctyl phthalate plasticizer leaches from new plastics used in closed aquaculture systems. Closed systems employing new plastics probably should be flushed for about 10 days with warm fresh water before they are put into use.

Chemical and biochemical oxygen demands were measured in the feeds used and in the inlet-outlet water at some freshwater trout farms. The oxygen consuming potential of 1 kg feed corresponded to 5–10 population equivalents. The biochemical oxidation rate during 10 days of the “net loading” (BOD outlet-BOD inlet) was equal to that of sewage. Characterizing the organic loadings from fish farms in terms of population equivalants therefore seems proper. The regression of COD on BOD 7 was also calculated.

Skin conditions, especially those of unknown aetiology, are often reported in rainbow trout (Oncorhynchus mykiss) aquaculture and are a true challenge for the trout industry. Red mark syndrome (RMS) is a skin condition affecting cultured rainbow trout, which first appeared in the United States of America (USA) in the late-1960s, then referred to as strawberry disease. It later appeared in Europe in the 1980s and was reported in the United Kingdom (UK) in late 2003. Since then, it has quickly spread to the rest of Europe and more recently has been reported in the Middle East, the Americas and Asia. Due to the downgrading of affected fish, RMS can cause significant economic loss to the rainbow trout industry. Several papers have described the histology associated with RMS in detail, and there is a good case definition for the disease. Although the aetiology has not yet been confirmed, two pathogens have been associated with the disease: a Rickettsia-like organism (RLO), now identified as a Midichloria–like organism (MLO), and Flavobacterium psychrophilum, however, an association between the latter and RMS has not been supported in subsequent studies. Although the MLO has yet to be isolated, ultrastructural features resembling Rickettsiales order organisms have been observed in affected tissues and a strong positive correlation has been found between the MLO and RMS-affected fish using a variety of techniques. More recently papers have described a reproducible challenge model based on cohabitation, which has been used to investigate the disease dynamics of RMS under controlled conditions. This review aims to examine the current state of knowledge relating to RMS and to highlight where there are gaps in this knowledge.

This paper assesses the economic feasibility of cage aquaculture in the offshore wind farm area of Changhua, Taiwan. According to the cost-benefit analysis, the results of cage aquaculture simulation for three species are economically feasible and the most suitable investment project is suggested to deploy 16 cages at the beginning. However, according to sensitivity analysis, at the current survival rates and purchasing prices, there is still a gap from the breakeven point in various scenarios. Hence, this paper argues that, if Taiwan's offshore wind power generation can be integrated with cage aquaculture, the conflict over sea area usage can be solved in order to create more employment opportunities.

This paper adopts the stochastic frontier model with flexible risk to analyze production risk, technical efficiency and its determinants of fish farms in four regions of Ghana including Greater Accra, Volta, Western and Ashanti regions. The study employs a two year panel data from 320 farms making a total of 640 observation through a random selection. The findings demonstrates that the translog model is best fit for the mean output function, whilst the input variables: hired labour, family labour, fingerlings, feed and other cost are identified to positively influence fish farm output at an increasing returns to scale. The paper also finds that feed and other cost are risk increasing inputs, whilst hired labour, family labour and fingerlings are identified to be risk decreasing inputs. The estimated average technical efficiency score of 0.74 shows that efficiency is compromised when the production technology is modeled without the flexible risk property which gave a score of 0.87. Additionally, the results show that age2, experience, pond area, gender, pond type and fish farming education significantly influence technical efficiency of farmers. This paper also highlights that technical efficiency of fish farms in the study area improved over time. In conclusion, the paper notes that on the average, 26% of potential output is lost due to technical inefficiency and production risk and given the present state of technology and input level, the possibility of enhancing production can be achieved by reducing technical inefficiency by 26% through adoption of practices of the best fish farm, whilst taking production risk into consideration.

This paper examines how value chain coordination affects the ability of aquaculture producers to engage in eco-certification. Through a comparison of global salmon and shrimp value chains, it is argued that production risks and producer capacity are key determinants in the type of chain coordination adopted by lead firms. The results challenge global value chain governance theory by indicating that it is hierarchical (or vertically integrated) forms of coordination that are associated with high capabilities and low risk rather than market forms of coordination. It is also shown that eco-certification is more likely to be adopted in value chains with more engaged forms of coordination. This in turn means that eco-certification is a far less ‘hands off’ form of regulation than widely thought. The paper concludes that for certification to engage producers operating under market forms of chain coordination new arrangements are needed that can respond to challenges of improving producer capability and production risk. Statement of relevance By understanding the role of risk and producer capability this paper contributes to improving the application and impact of eco-certification in global aquaculture production.

India is the world's second largest producer of farmed fish, and the state of Andhra Pradesh (AP) is by far the most important producer of farmed fish in India. Freshwater aquaculture has boomed in AP since the late 1970s, first with carps, then pangasius catfish. Over this period fish pond area and farmed fish production grew from nothing to reach 142,000 ha and 1.5 million tons, respectively. Despite its scale and dramatic consequences, the boom has received little attention in the international literature. The present paper addresses this gap by analyzing changes in the structure and conduct of each segment of AP's freshwater aquaculture value chain during four distinct phases of development (incubation, take-off, maturation and modernization). This analysis reveals that aquaculture development in AP shares many characteristics with agricultural commodity booms elsewhere in Asia. The paper contributes to the literature on crop booms by: 1) characterizing Southern domestic demand for agricultural products as an important but overlooked driver of agrarian development, and; 2) identifying interlinked processes of innovation and transformation in off-farm segments of the supply chain as a central feature of crop booms.

Feeding is a major factor that determines the production costs and water quality of aquaculture. Analysis of fish feeding behavior forms an important part of the feeding optimization. Fish feeding has generally been performed with automatic feeding machines which can lead to excessive or insufficient feeding. Recognition of fish feeding behavior can provide valuable input for optimizing feeding quantity. Due to the complexity of the environment and the uncertainty of fish behavior, the correlation and accuracy of behavior recognition are generally low. The accurate identification of fish feeding behavior till faces substantial challenges. This paper reviews the technical methods that have been used to identify fish feeding behavior in aquaculture over the past 30 years. The advantages and disadvantages of each method under different experimental conditions and applications are analyzed. Many methods are effective at evaluating and quantifying fish feeding intensity, but the recognition accuracy still needs further improvement. It is proposed by this paper that technologies such as data fusion and deep learning has great potential for improving the recognition of fish feeding behavior.

High incidence of cancer and other diseases have boosted the interest in herbal products to be used as alternatives to synthetic drugs worldwide. Plants that present biological activity are frequently processed, and their extracts are marketed as over-the-counter natural medicines. Such a trend is also observed in the aquaculture sector. The number of studies investigating the potential activity of plant-based products to substitute synthetic fish anesthetics has increased substantially over recent years. This paper summarizes the current data available and knowledge about the use of essential oils and active substances for fish sedation and anesthesia. Clove oil is the most commonly used plant-based anesthetic in aquaculture and several other studies have been conducted on the use of essential oils of basil, thyme, mint, rosemary, lavender, citronella, verbena and camphor for the different fish species. In recent years, active substances such as eugenol, menthol, myrcene, 1,8-cineole, linalool, limonene, citronellal, thymol, carvacrol, spathulenol, α- and β-pinene, 4-allylphenyl acetate and globulol, found as constituents of essential oils have also been investigated for sedation and anesthesia purposes in fish. This paper describes some of the sedative and anesthetic effects of essential oils and their active substances on the modulation of fish behavior, physiology and biochemistry. Such structured information could be useful for the aquaculture industry as natural anesthetics could be potentially more environmentally friendly, cost-effective and safer products than synthetic drugs for the management and welfare of aquatic organisms.

White spot syndrome virus (WSSV) is one of the most devastating pathogens, which inflicted huge losses to the shrimp farming sector in India and the world. The current study maps the WSSV research output during 1998–2017 using Web of Science (WoS) database. A total of 1786 tags were subjected to the present analysis which covers various parameters viz., growth, rank and global publications share, research collaborations and other bibliometric indicators like total citation counts, average citations per paper, and h-Index. India accounted for 17.24% of the global WSSV publications, and stood second among the 15 most productive countries in terms of number of publications in this period. The Indian researchers had networked with 23 collaborating partners across the world, of which USA, the lead collaborating country accounted for 18.51% of the total papers with international collaboration. The study showed a positive correlation between the grants awarded to the research laboratories and their research productivity. The paper provides quantitative analysis on the leading institutions and individual researchers, significantly contributing to the WSSV research in India. The journal Aquaculture carried the maximum number of research papers on WSSV from India (53 papers), followed by Fish and Shellfish Immunology (32 papers) and Diseases of Aquatic Organisms (25 papers). The analytical results of the present study provide insights into the trends of WSSV research in India and calls for concerted efforts to enhance focussed research on this significant threat to the 4.8 billion USD worth shrimp farming sector, which has the potential to reverse the fortunes of the farmers.

The Nan'ao Golden Scallop discussed in this paper is a new breed of noble scallop, Chlamys nobilis, produced by four generations of genetic breeding selections and two generations of culture demonstrations. Performed for the first time at Shantou University, the genetic breeding program was motivated by the need to reduce vulnerability and improve the adaptive capacity of noble scallops to the dynamic environment. This paper reviews the scientific evidences on aquaculture advantages of Nan'ao Golden Scallop, and identifies gaps in knowledge that require further research. From the analysis of published data, it is obvious that Nan'ao Golden Scallop is more nutritious and less susceptible to stress than common brown scallops. The high TCC of Nan'ao Golden Scallop up-regulate the expression of various immune related genes under stressful conditions. Since molluscs do not possess specific immunity, the information in this paper is very useful for improving the aquaculture performance of molluscs by selective breeding techniques.

The environmental effects of fish culture operations are important issues in Michigan as well as many other parts of the world. The State of Michigan Department of Natural Resources operates the Platte River State Fish Hatchery (PRSFH) located near Honor, Michigan (USA). This facility has a restrictive discharge permit that limits the input of phosphorus into the Platte River that subsequently drains into a downstream oligotrophic lake (Platte Lake). The permit has been violated on occasion in recent years. Hatchery managers and operators need to understand the cause of these violations and prevent them in the future; and at the same time meet production goals to satisfy fishery management objectives. This paper describes the development and application of models designed to quantitatively analyze these issues. First, a bioenergetic growth and consumption model is developed for juvenile coho ( Oncorhynchus kisutch ) and Chinook ( Oncorhynchus tshawytscha ) salmon to quantify the relationship between fish production and by-product phosphorus loads. Next, phosphorus mass balance equations are used to calculate the phosphorus discharge from the facility as a function of the by-product phosphorus load and the efficiency of various phosphorus removal equipment and processes. The accuracy and consistency of the energy and mass balance equations are verified using extensive measurements. The ability of the model to successfully match various aspects of system performance supports the contention that the bioenergetic modeling approach developed here can provide reliable estimates of salmonid growth and feed requirements for a variety of food compositions, rations, and temperatures. This capability, along with knowledge of the effectiveness of phosphorus removal equipment, forms the basis of a practical operational and management tool. An example of model utility is presented that analyzes the PRSFH phosphorus discharge and provides insights into why permit violations occurred in 2009 but not in 2010. The model demonstrates how to avoid food waste caused by over feeding, lower the food conversion ratio, and evaluate the effectiveness of phosphorus removal treatment processes. A steady-state version of the model can be used by managers to establish production goals that avoid future violations of the phosphorus discharge limits. Statement of relevance The environmental effects of fish culture operations are important issues in many parts of the world. This paper describes the development and application of models designed to quantitatively analyze the relationships among fish production, by-product phosphorus loads, and the phosphorus concentration of the discharge following treatment. The ability of the model to successfully match various aspects of system performance supports the contention that the bioenergetic modeling approach developed here can provide reliable estimates of salmonid growth and feed requirements for a variety of food compositions, rations, and temperatures. This capability, along with knowledge of the effectiveness of phosphorus removal equipment, forms the basis of a practical operational and management tool. The model demonstrates how to avoid food waste caused by over feeding, lower the food conversion ratio, and evaluate the effectiveness of phosphorus removal treatment processes. A steady-state version of the model can be used by managers to establish production goals that avoid future violations of the phosphorus discharge limits.

This paper reports on successful hatchery production of the winged pearl oyster, Pteria penguin, without the use of live micro-algae. Larval nutrition was provided by commercially available micro-algae concentrates, Instant Algae® (“Isochrysis 1800®” and “Pavlova 1800®”, Reed Mariculture Inc., San Jose, CA, USA). Larvae were first transferred to settlement tanks on day 17 when their mean antero-posterior measurement (APM) was 240.2 ± 8.6 μm. Approximately 6.4% of larvae survived to day 17 and more than 700,000 eyed pediveligers were transferred to settlement tanks between day 17 and day 25. Approximately 33,000 spat were harvested from spat collectors on day 105, representing a survival rate of 4.7% from the eyed pediveliger stage. Growth and development of larvae in this study were superior to those reported in a prior study that used a ternary live micro-algae diet to feed P. penguin larvae. Our results indicate that the products used in this study proved nutritious for P. penguin larvae and supported normal growth and development through settlement. The use of commercially available micro-algae concentrates as a replacement for live micro-algae in pearl oyster hatcheries supports development of simplified larval rearing protocols, without live micro-algae culture, that are more appropriate to Pacific island nations. Statement of relevance This paper reports for the first time on successful hatchery production of pearl oysters without the use of live micro-algae. Successful replacement of live micro-algae with commercially available micro-algae concentrates as a larval food source supports development of simpler, cheaper hatchery facilities, and larval rearing protocols that are more appropriate to Pacific island nations.

In the pioneering period (1970s) of Norwegian salmon and trout aquaculture, the biological knowledge underlying this industry evolved in an institutional world of open science. Universities developed novel breeding techniques, and small grow out mom-and-pop farms implemented them. Eyed eggs were generic and standardized products, and traded at the lowest possible cost. As an eyed egg, the fry and in particular the eyes are visible through the membrane. The interplay between the regimes of open science and proprietary science has changed significantly in salmon aquaculture over the last two decades. One aspect of this change is that husbandry breeding has become more industrialized and subsequently more controlled by large, specialized and capital intensive breeding corporations. This paper explores this development from the perspectives of process-oriented institutional theory. We identify critical junctures in the coevolution of the breeding and grow-out sectors, and analyze how these junctures structure and change the direction of industrial and economic development. Ultimately, the generic, standardized and undervalued eyed eggs were subject to revaluation by the novel dominant international actors in the Atlantic salmon industry. We primarily draw data from interviews with core actors and informants at relevant universities, breeding companies and governmental agencies, as well as from white papers and other secondary material.

The rapid growth of the aquaculture sector over the past forty years can be closely linked to advances in science and technology. Some innovations in biotechnology have proven more controversial than others, and none more so than proposals for transgenic fish. Such innovations introduce concerns for the responsible governance of research and innovation for aquaculture, particularly in recognition of the significant uncertainties and high stakes characterising these technologies. This paper argues in favour of a participatory approach to the governance of contentious aquaculture technologies that includes an ‘upstream’ regard for their ethical and social implications. From this point of departure, the paper presents empirical research that employed one particular approach to engage aquaculture stakeholders from Northern Europe in deliberation over the ethical and social considerations of transgenic growth-enhanced salmon, using the ‘ethical matrix’ tool. This research explores the complexity of considerations raised by these small groups of diverse and knowledgeable stakeholders across workshops in Germany, Norway and the United Kingdom, and links them with wider ethical discussions in the bioethics literature. The dual ambitions of the paper are to first provide insights into an applied approach for incorporating ethical reasoning in processes for responsible aquaculture techno-innovation, and second to provide an appreciation for the plurality of considerations that decision-makers need to navigate and carefully weigh when reaching a decision on the appropriateness of the particular transgenic growth-enhanced salmon.

Population increase, food security, employment, stresses on the fresh water resources and uncertainty associated with wild fish stocks are key parameters driving the demand for aquaculture expansion. Limitation in adequate waters in the coastal and near-shore sites for aquaculture development and the interactions within and from other coastal services forces the fish farming industry to move further offshore. Impact on the environment is an increasing concern that has to be considered in any aquaculture system designing. Moving further offshore could provide a better return on investment through various factors such as reduced mortality, better growth rates, less diseases and net fouling. However, moving offshore comes with a new set of challenges in withstanding severe weather conditions and safe and economic functioning of the aquaculture systems. Currently, the offshore fish cage design concepts are in their infancy and there is a race towards an optimum cage design for the offshore environment. Hence, in the aim of deriving an optimum cage design concept, this paper attempts to apply a holistic and theoretical approach to fish cage designing. By the application of theory of design, but different from the traditional engineering designing process, the paper proposes a conceptual framework and a cage design concept for offshore fish cage designing.