Pacu's. Convicts that won't fit in their mouths... I also have a snowflake eel in with my 9" oscar and no prob.. THe earlier fish I have kept with Oscars.. Now I have what some Keepers don't like much... A non specie racist tank... A couple africans , a supposed Flowerhorn, Convict , Texas, About to pick up a 110 so they can really play!!! Oh ya.. Mono, Scats.... Dempsy's shouldn't be a prob after they all adjust... I've even seen an aro,pacu,clown knife, and oscar housed together in the same 55 octogon... Oh ya cats....