Yes, it’s probably true that a transparent land-dweller would have a lot of UV-related issues that aren’t as big a problem for fish. But – pedantry alert! –
Transparent fish … have had to give up their scales
Not all of them. I have a bunch of glowlight tetras (for example), who have transparent flesh but also have scales that seem to have black rims – you can see the pattern of the scales. Meanwhile their cousin, the glass bloodfin tetra, is clear but you can’t see the scales (though it does have scales).
Even ‘scaleless’ fish tend to have scales, though they may be very small.
and I think mostly prefer darker habitats.
Not sure about that, either. In my tank, my one glass bloodfin swims up near the surface, while the glowlights tend to prefer being at the mid-level (~15-30 cm below the surface) during the day, and low/among plants in the evening.
Meanwhile the very-much-opaque rainbowfish are mid-level day and night.
Eh. Who knows what goes through their fishy little brains?
