I had one wipe out my whole tank. Including my mala, which I miss. Took two huge chunks out of him, healed from the first one but the second one was to much. It's possible to keep these with others, but it's only been done in HUGE tanks. A 240 won't be enough for either aimara or artc. They both get big, the catfish will grow faster. Mine grew from 16 inches when I acquired it to 24 in the course of 8 months or so and showed no signs of slowing. They both come from rivers. Idk how the cat would act if a fish were to be more dominant then it, but honestly with the two, I imagine them fighting to the death, the aimara trying to defend itself, and the cat not giving up. Maybe not the first time but eventually. If I were you I'd find a new home for the cat. If you were to try a similar cat try the wyckii, I think you'll have better luck with. The artc is more active from what I've seen allowing it to show its aggression more, not to say wyckii's aren't aggressive, but their territory usually sticks to their hide where as the artc wants the whole tank upper regions included. The fish will eventually get larger than your 75gal itself. It's a fish that shouldn't be so readily available in the trade Imo. If you insist on trying to comm the two, the 240 I assume is the biggest you have, which would be best. How big is the aimara? I strongly advise against communing the two. Most species in the bagridae family might not have big teeth but they have incredibly strong jaws. Making them just as formidable as the aimara with its large teeth and strong bite(isn't quite as strong as the cats). If you do so provide plenty of hides, and a good amount of current.