Aquatic livestock, no matter how adorable or meanacing, is unpredictable at best. Fish can be on their best behavior one minute, then turn around and maul a tankmate, or worse yet, the aquarist. Many aquarium fish are territorial to a degree, with some just preferring a spot in the tank and letting other fish come and go as they please while others go ballistic at even the slightest hint of encroachment. Clownfish are on strangers to this, as we’ve seen first hand how badly they can beat each other up and how some can even draw blood when they attack an aquarium keeper.
In situations where extreme aggression is occurring, there are two options. Keep your hands out of the water and don’t intervene, which obviously doesn’t fix the situation, or remove the aggressive individual altogether. The latter option isn’t always easy to execute and nobody wants to get rid of a fish they’ve had for years, but to fully enjoy the aquarium, it is a must.