I've had an upside down catfish in my 20 gallon for at least 3 years. When I got him he was MAYBE an inch in size. Recently I had issues with him and moved him to my 55 gallon. But I'm confused, from my understanding upside down catfish are community fish? But he was picking on the two goldfish in the tank. So I tried to look him up again and he doesn't look like any pictures I've seen. He's almost solid black and about 4 inches long, while pictures have them more lacy or spotted colored. I'd have a picture but he's currently hiding under the filter fountains. And he's been doing better, and my 55 is semi-aggressive! Has a grown Convict, a Synodontis Ocellated catfish and 3 Jewel Cichilds in with him. In my 20 gallon he was always hiding in a log, but the in the 55 he's out and swimming around. Did he just want more room? Or is there multiple types of upside down and he's a semi-aggressive sort and not community? I originally had African cichlids in the 20 gallon tank, but they had a battle royale and randomly killed each other, after all being introduced at the same time. And growing up together. So my catfish was the only thing left in the tank. Maybe that's why he's aggressive? I'm just confused on what he is and why he's so mean.