I had a mated pair of GTs male 7in, female 5in, with 2 loaches 3in, 2 bubblebee catfish 3in, and 1 pleco 6in, in my 55gal. use to have a 4in red tailed shark but when i left the fry in the tank to be raised by momma, red tailed shark got picked on to the point where he decided to find another tank on his own. He failed. And i had a nice chunck of red tailed fish jerky to despose of. When they were spawning, they were more aggressive, but nothing more than a few raggid fins on the pleco from time to time. I started having problems when i left the fry with their mother. When they get older and venture out, all fish in the tank cant put enough space in between the fry and themselves and in turn become targets for mamas wrath.