Fish can become remarkably aggressive, even toward the hands that feed them. Many fish keepers tell stories and show off battle scars from their encounters with overly aggressive fish, often tossing in a few expletives and other choice descriptors. Most of this aggression comes from clownfish or the dreaded damsels, and fortunately there are ways of alleviating some of this. Before I go any farther, I will say that aggression and territoriality are two very strong instincts that a lot of fish posses, and fixing the issue to your satisfaction may never happen. But here’s a couple of tips. Try rearranging the scenery since fish usually center their territoriality around a certain part of the aquarium or even a single object. If the aggression is in a large community aquarium, try removing some of the other aggressive tank mates. If a fish feels threatened or there is an increased sense of competition, each fish will act more aggressively to promote its survival. If removing fish doesn’t work, try adding a mate to the particular mean fish. This may give you more of a headache than its worth, but a lot of times the fish will divert energy away from aggressive behaviors to a more proactive hobby, such as pursuing its mate sexually. Who knows, maybe you’ll end up with a tank full of hyper aggressive fish.