Researchers examining Australian damselfish have found small fry with asymmetrical ear bones are less likely to make it back to their reef homes after a stint out at sea (research paper, press release). This could be because fish at sea listen for the sounds of home in order to navigate (see the BBC coverage for more on this angle).
Stress factors such as temperature and acidity will probably increase the number of fish with funny ears, they say. Increased acidity reduces the amount of calcium around for making ear bones, and having to regulate internal pH against changing water pH will also have a negative impact (Reuters, New Scientist).
As warmer and more acidic oceans are likely to result from global warming, more fish are going to be swimming around lost.
“Five years ago we used to see them [damselfish] in the thousands; now they are not so plentiful. A lot more work needs to be done, but I suspect it has something to do with the development of ears in the fish,” says paper author Monica Gagliano, of the Australian Institute of Marine Science (The Australian).