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

Chair: Tommy Moore

R.P.Ellis (1), Mauricio A. Urbina (1,2), D. Phillips (3), R.W.Wilson (1)
1 Department of Biosciences, College of Life and Environmental Sciences, University of Exeter, Exeter, UK
2 Departamento de Zoología, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Casilla 160-C,
Concepción, Chile
3 Anglesey Aquaculture Ltd, Black Point, Beaumaris, LL58 8RR, United Kingdom

Background
Aquaculture is one of the fastest growing food production sectors globally. It now provides more fish for human consumption than wild-capture fisheries, offering the only foreseeable way to increase production in the face of human population growth. Understanding the threat climate change poses to this sector is therefore of vital socioeconomic importance. Traditionally aquaculture practices adopt an open, natural water flow-through system for fish production; with little environmental control these are particularly vulnerable to shifting climatic conditions. Recirculating aquaculture systems (RAS) are an alternative solution, minimising water use and environmental impacts, thus improving sustainability of intensive fish protein production. However, using RAS also produces unique water chemistry issues; specifically very high CO 2 levels and raised carbonate alkalinity. Understanding the challenges facing the organisms produced under these conditions is therefore a priority.

Methods
Working with 5 industry partners, covering a range of farming practices from open systems to RAS, we investigated the carbonate chemistry conditions experienced in situ over an annual cycle. We then investigated the impact of the unprecedented carbonate chemistry within RAS on the physiology, growth and health of a farmed species, the European sea bass.

Findings
Within each setting investigated, organisms are exposed to carbonate chemistry conditions that exceed traditional end of century high CO 2 projections. Furthermore, within RAS these conditions are unprecedented with respect to natural carbonate perturbations. Despite this the physiological tolerance of sea bass to such perturbation ensures RAS production remains viable commercially.

Conclusions
Understanding the carbonate conditions experienced within a range of UK aquaculture settings presently will help predict the impact of climate change for this sector. Furthermore, by working together it is clear aquaculture practitioners and researchers can improve the productivity and viability of RAS aquaculture, alongside improving understanding of the physiological tolerances of aquaculture species exposed to extreme high CO2 perturbations.