fish reared under high CO2 conditions showed no preference for either the unfamiliar or familiar school.
it is thought that carbon dioxide interferes with the functioning of neuroreceptors in the fish brains. Higher carbon dioxide levels change the concentration of ions (electrically charged atoms and molecules) in the fishes' blood, altering the way that the neuroreceptors work. This impairs basic senses, such as sight and smell, which are vital for recognition in fish.
These results could have serious implications for tropical fish, whose habitat is already threatened by climate change. "Familiarity is an important trait for defence, particularly in a predator-rich environment like a coral reef," says Miss Nadler. "Since half of all fish species in the world school at some point during their lives, including economically important species, these effects could be critical for species that rely on group-living to avoid predators.