Fish are losing their sense of smell because of a rise in CO2 levels, according to new research.
Scientists at the University of Exeter say that increased levels of carbon dioxide in the atmosphere is making oceans more acidic.
CO2 is absorbed by seawater forming carbonic acid.
There's a warning that without their smell, fish will find it more difficult to survive.
Fish use their sense of smell for lots of essential things: finding food and safe parts of the ocean to re-produce, recognising each other and, most importantly, sniffing out danger so they can avoid predators.
Since the 1800's ocean CO2 levels have risen by 43%.
It's predicted to be more than double the current level by the end of the century.
Dr Cosima Porteus led the study at the University of Exeter: "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," which is indicates that they're feeling anxious.
Scientists tested the fish's ability to respond to a series of different smells.
Although only sea bass were used in the research, the processes involved in the sense of smell are common to many species.
It means experts think these findings will also apply to other types of fish.
"By the end of the century, potentially even sooner, it could become more difficult to buy fish," Dr Cosima told Newsbeat.
"We might have to rely more on aquaculture, where fish aren't in the sea and don't have to worry about predators."
"But there are limits to how much we can increase that, especially in a growing population."