CO₂ in aquaculture

Aquaculture of fishes is increasingly using recirculation technology to conserve water and reduce the environmental footprint from production. Recirculating aquaculture systems (RAS) require an intensification of production, which gives rise to a number of water quality issues that must be considered, including the accumulation of carbon dioxide (CO₂). This chapter provides an initial overview on the excretion of CO₂ from fish and bacterial metabolism, before discussing what is currently being considered as safe levels, or levels of no-effect, of dissolved CO₂ for fish, highlighting some differences between aquaculture and ecological studies. The correlation between alkalinity and pH, and the chemical form of CO₂ is briefly covered, before providing an overview of current removal practices and technologies. The chapter provides an overview of the physiological effects of CO₂ in relation to aquaculture production, specifically feed intake, appetite, digestive function and growth, before considering the effects of CO₂ exposure on the ability of fish to migrate from fresh to seawater, in light of structural and functional changes in the gills. Finally, some pathologies associated with CO₂ exposure, such as nephrocalcinosis and eye cataracts are highlighted, before closing with an overview of interacting effects between CO₂ and other water quality variables, such as hypoxia or dissolved metals.