https://phys.org/news/2018-07-acidic-oceans-fish.html

The new study provides evidence that economically important species will be affected by elevated CO2, leaving fish vulnerable because it affects their ability to detect odours.

University of Exeter researcher Dr. Cosima Porteus, who led the study, said: "Our study is the first to examine the impact of rising carbon dioxide in the ocean on the olfactory system of fish. First we compared the behaviour of juvenile sea bass at CO2 levels typical of today's ocean conditions, and those predicted for the end of the century. Sea bass in acidic waters swam less and were less likely to respond when they encountered the smell of a predator. These fish were also more likely to "freeze" indicating anxiety."