I'd have never thought of this myself. I remember watching a documentary in the early 2000's that said dogs and cats can't actually see tv's properly beause of the frames per second the tv played. It was something like 60, while dogs and cat's see 90 or so frames a second, so the tv was too slow for them.
Modern TV's play more frames a second so dog's and cat's can actually see what;s on a flat screen just as well as they can see normal. (I didn't know this until I looked it up.)
But for some reason in my mind, I figured that if the most common house hold pets couldn't see tv properly then fish couldn't either. I mean they also live in water which is another added difficulty. (But I guess that would affect sound more than sight).