Interesting research.

https://www.sciencedaily.com/releases/2016/04/160428094451.htm

Hear no evil: Farmed fish found to be hard of hearing

Date:
April 28, 2016
Source:
University of Melbourne
Summary:
Half of the world's farmed fish have hearing loss due to a deformity of the earbone, new research has found for the first time. Like humans, fish have ears which are essential for hearing and balance, so the findings are significant for the welfare of farmed fish as well as the survival of captive-bred fish released into the wild for conservation purposes.