it really has to do with growing them together and crowding.
I have my 300g with 4 zebra tilapia, 3 red belly tilapia, 2 red devil, red terror, ab out 9 jack dempsy, a blue stripe pike, green terror, and about 60 or so smaller african/ca.
I really did not want to put all these in just the bigger ones but had to as a tank emergency forced me to put them all together. I did a move to try to lessen the population and as soon as I put the 9 largest who have grown together with the jack dempsy into a 230g all hell broke loose. When I put them back into the tank they grew up in peace returned.
The formula works more fish=less agression. Here in NYs China town all the shops over crowd their tanks to the max. We are talking thousands of dollars in one tank. Forget about agression. I dont know how they keep em alive. They really know what they're doing.
When one fish misbehaves, they scoop it out, put it in a bucket, and take it to the kitchen to show it where it will be if it keeps it up. Maybe they throw it in a pan and flip it around some. The fish is so terrified it goes and tells its horror story to the other fish, and scares them nice too.