Betta fish fight to protect their territory, to ensure that they have enough food and also because they want to be “king of the hill” when it comes time for them to breed. These are genetic traits and you won’t be able to train your fish not to fight.
When you have two male Betta fish in your tank they will “flare” at each other (this means they puff flaring out their fins and gill covers, to make themselves look bigger and more threatening.) Often one fish will admit defeat and swim away, leaving the other male victorious.
When people began keeping and fighting Betta Fish, aggression was bred in them.
Most of the time male Bettas will only attack other males. However it is not unheard of for a male Betta fish to attack a new female or one that he feels threaten by, so it is always a good idea to keep your eye on your Betta fish when you first introduce another fish into the tank or if you are putting you Betta in with other fish.
Sometimes more aggressive Betta fish will nip or bite the other fish. So if you see this happening remove the aggressive one right way to avoid injuries.
How To Keep Your Betta Fish From Fighting
There really is only one way – don’t put two male Bettas in the same tank. If you only have one tank and two male Bettas, you have a couple of choices – the first is to use a “fish condo”.
Fish Condos: These are clear plastic containers with air holes that let the tank water flow through them. Depending on the size of your tank you may be able to fit in two, three or four space condo. Each Betta fish has its own space and you can put up visual barriers such as plants or java moss so that he can’t see the other Betta.
You can also put a single mesh divider in one section of your tank that will keep your male Betta fish separated from each other.