In all my years I've never had a Pleco latch onto another fish. I can say I've had several from many sub species. I do cater to them and feed them as the target fish in my tanks. I've had L14s & L24s with Stingrays and Angel's. I think as long as they are fed and not left to clean up scraps they should be fine, never had one adept at just eating algae off rocks or glass, but Otocinclus are phenomenal at it, you can get a bunch...they won't damage live plants either.