Nastiest I've kept was Hemibagrus Wyckioides (Asian Redtail). Before I sold mine, he'd racked up a pretty big kill list. Cleared a tank full of C.A/S.A cichlids (red devils, festae, managuensis, midas, dovii, umbee, name it and he killed it at some point). At 12 inches, it even killed a slightly larger H. Wyckii... they were dividered in a 90g, eventually the inevitable happened, someone knocked over the divider overnight and I found a dead wyckii and a slightly battered ARTC. I was pretty pissed, the wyckii cost me a good chunk of money. I had a 16 inch male dovii in solitary confinement in a 180g tank, and since the ARTC was outgrowing the 90 it was in (IIRC about 1.5 feet at the time), I decided to try adding it to the dovii's tank over a day under my supervision. The cat wrestled with the dovii immediately after being added to the tank, after about 5 min of liplocking the 2 left each other alone. Phone rang, went upstairs, ended up chatting. About 5 minutes into the conversation, I heard a loud thump, a bunch of splashing followed by another thump. I ran downstairs, the ARTC had the dovii pinned in the top corners of the tank, and was repeatedly slamming it out of the water into the coverglass. No serious damage was done, just some fin rips and missing scales on the dovii. Sold the dovii to my friend the next day and kept the ARTC by itself in the 180.
Wyckii can be evil as well, but IME wyckioides are just that little bit worse.
