Yes, I know. Some will say that ‘fishes’ is wrong, but as a matter of fact, it is now common to find both ‘fish’ and ‘fishes’ in a dictionary. And anyway, this idiom does use ‘fishes’ (So there!).
But far from picking an argument about whether or not this plural is correct, this post is all about an idiom that refers to health in an extremely funny way. What type of health problem does this idiom refer to?