in my experiance pirhanas love catfish as food and none can survive un less you have a large tank with plenty of hiding spots for the cat when my curent batch of redbellys were about 3 inches i had a 10 inch channel cat in there for about a week then they got tierd of him i woke up to a dead channel cat. sorry for your loss by the way
I do not mean to belittle your lose but this is what they do in the wild this is what they should do in home aquaria.
My tsn regularly will ingest fish that I would suppose are to big to be eaten. If it is in there with the tsn, I automatically write it off as a possible food source.
Fish eat fish. And some fish really go to town eating other fish.