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

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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.