Well....i"m not a marine biologist or anything like that so I could be way way way off here...but fish really don't have to worry about rehydrating their eyes like people do....they do live in water after all
I'd be interested to here an authentic answer to this...
Most fish have a coating over the eye so as to protect them
I may also shield to some degree the amount of light and spectrum too. This gives them and advantage by never having to close there eyes they are watch all the time. The slimy
non-adhesive coating allows debris to slid right off.
Too low down the phyla. Our eyes develop behind an unbroken covering, then it breaches, and, blink, we have eyelids. Fish are 'done' before they get that far along, so the covering on their eyes never breaches. Howzzat for a nice piece of flimflam?