I'm not sure I completely agree on the pleco must come out. There are several ray keepers that keep plecos with rays. I'm not saying there is no risk, in fact, if a small ray is introduced one night is all it would take if the pleco wanted to attack/harass the pup to death. Not sure on your plecos temperment as some can get very territorial and agressive others could care less. Alot of it depends on size of the tank, if it gets enough food, and temperment. I would however error on the side of caution. Plecos have killed rays. They are like an armored tank with teeth.