Caleb T. Hasler

In many freshwater ecosystems, carbon dioxide (CO 2 ) is increasing. Unknown are the risks that high CO 2 poses for freshwater organisms, especially fish. The objective of this study was to determine how CO 2 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, 1814)), and rainbow trout ( Oncorhynchus mykiss (Walbaum, 1792)). For this study, fish stayed in control (1100 microatmospheres (µatm)) or elevated (5236 µatm) CO 2 levels 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 CO 2 affected the growth rate, feeding rate, or behaviour in any of these species. The standard metabolic rate in Arctic charr differed based on CO 2 exposure. Therefore, salmonids can withstand short periods of elevated CO 2 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 CO 2 on young salmonids.