Using physiology to optimise water quality and the sustainability of intensive recirculating aquaculture systems (RAS)

Lead Research Organisation: University of Exeter
Department Name: Biosciences


The current FLIP proposal builds upon an existing BBSRC Industrial Partnership Award in collaboration with Skretting (the largest global producer of aquaculture feed). The existing 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 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 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. This is compensated by large scale aeration of the recirculating water which effectively restores oxygen, but is often insufficient to removal all the animal's waste carbon dioxide which subsequently acidifies the water. To deal with this pH problem RAS operators added huge amounts of alkali (1-2 tonnes of caustic soda per day) at considerable cost. However, this pH compensation measure is now realised to create further water quality issues, specifically high alkalinity and low calcium within the water. These secondary changes are known to impair the physiology and energetics of fish, and are therefore suspecting of 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.

Technical Summary

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 changes in water quality that are associated with maintenance of land-based RAS (specifically high alkalinity and low Ca2+ caused by measures to compensate for CO2-induced acidification) that impair the physiology (acid-base, ion/osmotic regulation, respiration) and energetics of feeding and growth in fish. The interchange will further result in a cost-benefit analysis of strategies that can be employed to mitigate these RAS water quality problems, and therefore to optimise fish protein production and its sustainability (including potential risks of the under- or over-application of any mitigation technologies). 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

Planned Impact

Types of Beneficiaries and How They Might Benefit:

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, acid-base and ionoregulatory 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).

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 changes in water quality 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. 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.


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Description We have completed a thorough analysis of the water chemistry in the largest seawater recirculating aquaculture system (RAS) in Europe, based in Anglesey. This revealed that despite water quality management effort to keep dissolve CO2 levels as low as possible, the actual CO2 within this RAS system was 6-7 times higher than normal levels associated with the open ocean (i.e. in equilibrium with atmospheric CO2 levels), and almost 3 times higher than levels predicted for end-of-the-century under climate change scenarios. Furthermore the attempts to buffer the pH effects of this elevated CO2 (i.e. acidification) created other major changes in the seawater chemistry that are very atypical of natural conditions. Specifically the alkalinity is extremely high (4 times higher than normal seawater), and calcium concentration is much lower (approximately half). The unnatural combination of highly elevated CO2 and alkalinity, and considerably reduce calcium, are expected to impair normal physiological functions of fish in aquaculture (specifically acid-base balance and osmoregulation) with long-term consequences for the efficiency of growth and resistance to disease. Physiological experiments on fish feeding at high rates (as in aquaculture) show that fish undergo a large blood alkalosis (rise in blood pH and bicarbonate known as the "alkaline tide"). Fish need to recover from this blood acid-base disturbance after feeding, which requires energy as well as the appropriate ionic gradients across the gills and appropriate ion concentrations in the external seawater to ensure efficient excretion of the excess base and a return to normal physiological status. However, the water chemistry conditions found in RAS are predicted to impair this process.
Exploitation Route We are using this information within a second BBSRC FLIP project which is currently ongoing.
Sectors Agriculture, Food and Drink,Environment

Description On the basis of our research an aquaculture company (Anglesey Aquaculture Ltd.) have changed their practices for regulating water chemistry in a 10,000 tonne seawater recirculating system (RAS). This has improved health and safety issues for staff at the site, as well as reduced some of the difficulties associated with previous practices within the aquaculture industry.
First Year Of Impact 2015
Sector Agriculture, Food and Drink,Environment
Description AquaLeap: Innovation in Genetics and Breeding to Advance UK Aquaculture Production
Amount £1,700,000 (GBP)
Funding ID BB/S004300/1 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 01/2019 
End 12/2021
Description ROBUST-SMOLT: Impact of early life history in freshwater recirculation aquaculture systems on salmon robustness and susceptibility to disease at sea.
Amount £1,500,000 (GBP)
Funding ID BB/S004122/1 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 01/2019 
End 12/2021
Description The role of water chemistry in zebrafish welfare and reproducibility of research studies
Amount £351,653 (GBP)
Funding ID NC/S001123/1 
Organisation National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs) 
Sector Charity/Non Profit
Country United Kingdom
Start 08/2018 
End 08/2020
Description Using physiology to improve the health and sustainability of cleaner fish (lumpfish) production for the salmon aquaculture industry
Amount £82,000 (GBP)
Funding ID 2071339 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 09/2018 
End 09/2022