I've searched the forums but couldn't find a thread listing fish that are mostly or all vegetarian. It seems amazing to me that you could feed it organic spinach or cucumber or bok choy. Thanks a bunch!
In case you didn't know, the better terms to use are herbivorous (no meat, strictly vegetation) or omnivorous (some meat and vegetation). By posting this thread, are you wanting to finding out what fish are herbivorous, or were you just remarking at the fact that there are herbivorous fish?
Heterotilapia Multispinosa (Rainbow Cichlids) feed entirely on algae in the wild.