I have seen small flounder in shops during my visits but have never thought much about them.I wasn't aware that they ate fish,I figured they fed on various worms and other lower organisms.....very interesting.
The species you have would be the one that I'd be most interested in trying.the more common "hog-choker" and the other brackish flounders are more likely to eat worms, but everything ive found and tried points to these larger FW south american species eating mostly small fish. Mine is currently plastered to the back glass of the tank and trying to blend in to the black background while he tries to get some of the minnows hanging out under the spraybar.