As human-emitted carbon dioxide dissolves in the oceans and turns them more acidic, some fish could struggle to see fast-moving details in their environment, a new study suggests. Scientists have found that ocean acidification can impair fish's smell and hearing, but they know less about its impacts on eyesight. So researchers turned to the spiny damselfish (Acanthochromis polyacanthus, pictured) a common ocean-dwelling fish that’s easy to breed for lab study. Much like humans can see TVs flicker, these swimmers use their eyes to detect rapid light flickers. Curious how higher-CO2 conditions would affect this ability, researchers placed the animals in water tanks with different levels of carbon dioxide and shone lights at various flickering rates. To assess whether the fish discerned individual flickers, the team used electrodes to measure nerve-cell activity deep in the eyes. If the electrodes detected activity in tandem with the flashing, the fish had recognized the flickers. In damselfish exposed to CO2 levels projected for 2100, this activity pattern stopped after the flashing rate reached 79 times per second. That’s more than 10% slower than the maximum 89 flashes per second that fish exposed to modern-day CO2 levels discerned, the researchers report in The Journal of Experimental Biology. Fish with impaired flicker detection could be more vulnerable to predators, the team suggests. The higher-CO2 conditions likely disrupt the GABA family of nerve-cell proteins, which are involved in vision and behavior, the researchers say. Other animals possess these proteins, so many could suffer similar problems in higher-CO2 water.