so i work at a petsmart and we have 2 29gallon hospital tanks in the the quarintine room at the store so when we get sick fish we have to quarintine the and we generally use one for aggressive fish and one for smaller or non aggressive fish, and the other day i had to quarintine a male black molle who had a lil bit of a bacterial infection so i put him in a tank with two 4-5inch oscars and a few other cichlids, bigger caricins, sharks (cats, and loaches,and minnows) so some mildly aggressive fish and hardier fish but assoon as i dropped him in there he started to go after one of the oscars and the entire time it took me to close the back he chased the oscars. the next day i went into the quarintine room one oscar was dead along with a few others and he was on to one of the barbs. this fiash was a beast killed anoscar and almost killed the other along wit some other fish i cannot believe this 3 inch mollie was so badass