Betta Fish Aggressive Behavior Betta fish are very possessive creatures. These fish will attack any intruders to defend their territory. The betta fish evolved into the hostile fish you keep as pets today through years of selective breeding and domestication. While attempting to defend their food, these fish can attack other fish.

Male betta fish tend to be more aggressive. They set up territories that they defend with their lives. When another male betta is introduced into the tank, the original male will start to display warning signs. These warning signs include flaring their gills and spreading out their fins in an attempt to make themselves look like a serious threat.

which betta is more aggressive