What size tank?
Gourmis have similar behavior as bettas, males fight, although not as viciously, the constant stress from territorial and dominace battles can make the individual on the bottom of the pecking order stressed out and more prone to illness, or starvation because the dominate fish does not allow it to eat.
It is not difficult to tell male and female blue gourmis apart. The dorsal, anal and tail fins of the male will be more pointed, and in the female these fins will be rounder. Also, the female, when seen head on, will be more plumper behind the pectoral fins. It is advisable that you have two females for every one male in order to reduce the aggression. Females can be just as aggressive as males, though, especially if they are larger.
The bad part is that gourmis are also highly territorial, and can be so with other fish. If your tank does not have a large surface area, your groumis can dominate the entire tank and not allow any other fish to the surface to feed. I have known cases of blue gourmi being placed in community tanks, and have descimated their tankmates because they were too crowded. Blue Gourmi also grow a good 8"-10", so nothing short of 55gallons or more might satisfy them biologically or territorially.
Some people have gotten their gourmi to live "peacefully" with other fish. I don't know exactly how they've done that, it must depend upon the individual fish. I have one 2" bably blue gourmai male that is actually the bottom of the pecking order in my tank, even where the other fish are concerned, so I have no trouble with him. Other people have super dominate fish that kill the entire tank. Make sure your tank is plently well decorated to give those being chased a place to hide, and make sure you do not crowd them. Trading in the "mean" fish does not garentee you'll get a more "peaceful" gourmi. Gourmi's can be great community fish so long as they are given the proper amount of room to establish their territories
~~Colesea