I've looked for literature in the past in relation to fish and CO2 tolerance and to honest didn’t find much. What is available will generally relate to aquaculture systems with a lot of work been done on salmonid species that are associated with clean very well oxygenated waters and probably have a lower tolerance than most. I’m a bit pressed for time at the moment but when I get the chance I’ll have another look for this stuff and post anything here that is relevant.

Regards
Neil