Are you sure of your Synodontis euptera identification? Many synos come into the trade mididentified, for example I have a lovely placid fully gorwn (for a hobby fish) ~10cm SL Synodontis congica that would not "hurt a fly" that was ordered online as a Synodontis notata, that reach ~25cm in the hobby and can vary hugely in temprement and will happily munch on small tankmates (I thankfully have since acquired a well behaved notata, but I am not prepared to risk it with my recently bought group of Pareitropius cf. mandevillei).
Can you be a lot more precise about your "pleco catfish"? There are just a few... hundred!
http/www.planetcatfish.com/catelog/family.php?family_id=4
Euptera can be a bit fiesty and spiteful, especially with smaller tankmates (known to predate and kill fish like Neon Tetras quite happily), but should be reasonably compatable with fish that will reach a similar size in the hobby (15-20cm SL, length excluding the tail fin).