I had a few extra severum juvies under half an inch, put 2 with the GT and Oscar, one got absolutely slaughtered(it's head was laying on the bottom of the tank) and the other is now almost 2 inches. He will go right up to the Oscar and GT, until of course the 6 inch GT gets pissed and tries to catch him. Life I guess.
I had a 3 inch male convict survive for 4 months with a shoal of 9 red belly piranha ....The p's started off has dime sized babes with the con....Four months later , the little dimer turned into 4-5 inch eating machines....I found the convict all chewed up one morning, head missing.....
I had a few goldfish survive, they were pretty fast too. Girlfriend made me move them because she got attached to them. Moved them to an amphibious tank where they lived for a few more weeks. They went MIA and I had a VERY fat toad..