I had three pumpkinseeds in with my green sunfish for 2 months. All were the same size, 4". Plenty of hiding spaces. The green was obviously getting more of the food as he's now 5"+. Two pumpkinseeds died though. I think he just looks at them and they die! When I gave him feeder guppies once, they died without having any bite marks or anything physically wrong with them. Do you think he's scaring other fish to death? Pumpkinseeds are supposed to be aggressive, but they are nothing compared to the green sunfish. I swear if he could he'd jump the tank and come after me one day while I watch him.