Optimising ammonia to improve sustainability in highly buffered recirculating aquaculture systems (RAS)

The current FLIP proposal builds upon an existing BBSRC Industrial Partnership Award in collaboration with Skretting (the largest global producer of aquaculture feed). The latter IPA project is based on a novel manipulation of diets that has already been demonstrated to improve the efficiency of converting food into growth by a remarkable 20 % under laboratory conditions. It uses laboratory studies with live fish to assess the energetic costs and health implications of feeding in aquaculture fish, and then to design optimal diet compositions to minimise these costs. It aims to make energetic savings for the fish in particular regarding acid-base and salt balance following a meal, and minimise how these natural disturbances impact upon respiratory gas exchange and excretory processes. The present FLIP proposal will use similar approaches to the above current BBSRC-funded project. However, whereas the current BBSRC-IPA project addresses dietary issues, this FLIP proposal specifically addresses newly discovered water quality changes that are particularly associated with intensive recirculating aquaculture systems (RAS). The present FLIP proposal is also linked to another FLIP project (started June 2015) as both stem from water quality issues experienced by intensive RAS. Specifically the artificially enhanced buffer capacity of the water (raised NaHCO3 as part of the regulation of water pH). In turn this inhibits ammonia excretion in fish (through buffering of the normally acidic gill boundary layer), causing increases in blood ammonia which can result in undesirable changes in whole animal performance.

The present FLIP proposal seeks to use a 2-way interchange between academia and industry to address previously unconsidered factors that can have a major influence on the biology and efficiency of growth in fish. By facilitating an interchange of academic and industrial personnel between their respective sites this project aims to address these non-ideal changes in water chemistry associated with intensive recirculating aquaculture systems (RAS). It aims to establish (and ideally prevent) previously unrecognised energetic costs for fish associated with regulation of internal ammonia levels caused by these water quality issues that can impair health, welfare, growth and ultimately the production efficiency in aquaculture. It is a collaboration with Anglesey Aquaculture Ltd (AAL), the largest marine RAS in Europe and the UK's only farm for seabass, a high value and commercially important fish. This form of land-based aquaculture is increasingly promoted worldwide due to its sustainability in terms of low water use and minimising environmental problems from waste products. However, the intensity of the aquaculture conditions creates water quality problems that must be countered, primarily a consumption of oxygen and excretion of carbon dioxide by the fish that acidifies the water. To deal with this pH problem RAS operators add huge amounts of alkali (hydroxide or bicarbonate). However, this pH compensation measure creates a further water quality issue, specifically high alkalinity (and therefore buffer capacity), whilst CO2 is only partially reduced. These secondary changes are known to inhibit the excretion of ammonia by fish gills, raising internal blood levels of ammonia, and ultimately impair the general physiology and energetics of fish, and negatively impacting their feeding and growth.

By facilitating a 2-way transfer of knowledge and skills (via direct secondments of one academic and one industry interchanger, at each other's site), this FLIP project aims to provide a cost-effective, evidence-based solution(s) to these specific water quality issues. Furthermore, we aim to embed a culture of problem-solving through academic-industrial collaboration into the fabric of both organisations such that future problems associated with sustainable production of fish can be avoided or mitigated in a timely fashion.

This FLIP proposal links with a current BBSRC IPA award (BB/J00913X/1) which is a collaboration with Skretting (the largest global producer of aquaculture feed) based on a novel manipulation of diets that has already been demonstrated to improve the efficiency of converting food into growth by a remarkable 20% under lab conditions. The present FLIP proposal will use similar in vivo physiological and biochemical approaches but instead of addressing dietary issues, it specifically addresses the water quality changes associated with intensive recirculating aquaculture systems (RAS), which could be a limitation to their efficiency and sustainability worldwide. This FLIP is a collaboration with Anglesey Aquaculture Ltd (AAL), the largest marine RAS in Europe and the UK's only seabass farm. The proposal seeks to use a 2-way interchange between academia and industry to provide evidence-based solutions resulting from fundamental physiological studies to address previously unconsidered factors that can have a major influence on the health and efficiency of growth in fish. It aims to assess the impacts on fish of artificially high buffer capacity in the water that is associated with maintenance of land-based RAS (specifically high alkalinity caused by measures to compensate for CO2-induced acidification). This can impair the abililty of the fish to excrete toxic waste ammonia and ultimately impair the energetics, feeding and growth in fish. The interchange will further result in a cost-benefit analysis of strategies that can be employed to mitigate this RAS water quality issue, and therefore to optimise fish protein production and its sustainability (including potential risks of any mitigation strategies). Finally we will compare aquaculture impacts of the current non-ideal water quality scenario with potential mitigation options using small-scale trials at the commercial site.

Academia:
Beneficiaries will include fellow researchers worldwide within integrative and comparative physiology, but also researchers within the fields of animal nutrition, and post-genomic technologies. The breadth of the data produced in Objectives 1 and 2 will be of interest to a broad range of physiologists, including those studying the respiratory, metabolic, and nitrogen excretion functions in animals and their integration with feeding and energetics. The planned research should advance our fundamental understanding of these functions, and as such will be disseminated through international physiological conferences and the highest quality peer-reviewed journals within the field (e.g. American J. Physiology; J. Experimental Biology).

Business/Industry:
The project will also potentially have direct and immediate economic benefits to the aquaculture industry both in the UK and globally. Objective 1 will establish the potential physiological and energetic costs of the high buffer capacity of water specific to intensive RAS mentioned in the summaries above. This will be done using laboratory experiments, but WP3 (Objective 3) also involves commercial-scale feeding/growth trials that will test the potential mitigation options that are suggested by WP2 (Objective 2). This will be of great interest to the industrial partner (Anglesey Aquaculture Ltd, the only sea bass farm in the UK and the largest marine RAS in Europe), but also to the aquaculture industry globally. We already have interest from several other aquaculture companies using RAS (specifically the large scale culture of salmon smolts in freshwater RAS in Scotland). It will also be of interest to researchers and companies within the field of animal nutrition. This part of the project will therefore be disseminated through key international conferences in the field (e.g. International Symposium of Fish Nutrition and Feed) and the highest impact peer-reviewed journals oriented towards aquaculture and animal nutrition (e.g. Aquaculture; Aquaculture Nutrition; J. Nutrition; British J. Nutrition). The outcomes will additionally inform important non-academic audiences such as small scale fish farmers, through a variety of outputs. For example, companies such as Skretting publish a company newsletter ("Outlook") 2 to 3 times per year, and we would also aim to publish popular science articles in the Trade magazines (e.g. Fish Farming International; Fish Farmer; Aquatic Expert). WP3 (Objective 3) also has the potential to make significant improvements to food conversion efficiency in fish. Even small % improvements in growth efficiency can generate significant economic and environmental benefits for aquaculture. This would in turn help reduce the need for increasingly expensive and diminishingly available marine resources that are used to make fishmeal, currently the main ingredient of fish food for trout and salmon aquaculture. Any reduction in the need for fishmeal, whilst maintaining the same fish production in aquaculture, would therefore have positive environmental benefits. For example, our improved growth efficiency due to better water quality should simultaneously reduce the eutrophication problem created by nitrogen and phosphorous in aquaculture effluents which is a major environmental limitation of fish farms. Outputs that support this hypothesis will therefore be communicated through the appropriate channels (e.g. Environment Agency, Defra etc.) to promote such environmentally-friendly practices that may improve the long term sustainability of aquaculture.

General Public:
Improved efficiency of fish production, should eventually have a knock-on effect on the retail price of fish ,which would benefit the general public as consumers of fish. Additional publicity based on the improved health of aquaculture fish and subsequent quality of the marketed product should stimulate consumer interest in this healthy source protein and oils.