An extraordinary 10 to 60 percent or even more of both fresh and saltwater fish species will be unable to survive in their current areas due to abrupt climate change in the coming decades. Impacts on ecosystems will likely be profound. https://science.sciencemag.org/content/369/6499/65

'In the best-case scenario the authors considered – where the climate heats a total of 1.5C – only 10% of the surveyed species would be at risk...'

3-5C within decades is more likely (though perhaps still avoidable?).

http://web.archive.org/web/20210114221255/https://amp.theguardian.com/environment/2020/jul/02/fish-species-survival-climate-warming-study

'Dahlke noted this assessment was conservative – it does not take into account other climate crisis factors that could affect marine life, like ocean acidification, that could amplify the effects on sensitive populations.'

http://web.archive.org/web/20210114221255/https://amp.theguardian.com/environment/2020/jul/02/fish-species-survival-climate-warming-study