Short-term exposure of near-future CO2 has limited influence on the energetics and behaviour of young-of-year salmonids

In many freshwater ecosystems carbon dioxide (CO2) is increasing. Unknown are the risks that high CO2 poses for freshwater organisms, especially for fish. The objective of this study was to determine how CO2 may influence the growth rate, metabolic rate, feeding rate, and volitional behaviour of young-of-year Arctic charr (Salvelinus alpinus; Linnaeus, 1758), brook charr (Salvelinus fontinalis; Mitchill, 1815), and rainbow trout (Oncorhynchus mykiss; Walbaum, 1792). For this study, fish stayed in control CO2 levels (1,100 µatm) or elevated CO2 (5,236 µatm) for 15 days. During this time metabolic rate and behavioural tests were conducted on alternating days for each treatment. Weight and length of each fish were taken on days 0, 7 and 15. There was no evidence that elevated CO2 affected the growth rate, feeding rate, or behaviour in any of these species. The standard metabolic rate in Arctic charr did differ based on CO2 exposure. Therefore, salmonids can withstand short periods of elevated CO2 under these conditions. By comparing closely related species, the implications of this work are more ecologically relevant and will also help industry quantify the effects of high CO2 on young salmonids.