Sometimes, despite the careful planning we put into selecting fish for our tank, an aggressive fish may still taunt and terrorize her tankmates. Is it possible to redirect or retrain an aggressive fish? Not always. And if you have a fish that is truly too aggressive for your tank, your only choices may be moving her to a separate tank, returning her to your supplier or exchanging her with another hobbyist whose fish may be more compatible. Before you make that choice, examine the possible reasons behind her aggressive behavior. This article details some of the most common problems and their solution.

Some species are naturally aggressive. Research the natural aggressiveness of fish that interest you before you purchase them. This way, you can select compatible fish that can all happily coexist in your community tank.

Move the décor around in the aquarium or add additional hiding places to help confuse the fish's territories. Rearranging the décor may be particularly helpful when introducing new fish. This tactic may keep the fish apart, but it may only be temporary. As a last resort, you may have to keep one of the fish in another aquarium setup.

Your tank may not be large enough. Introducing a second big fish into a tank made to house just one fish or an overcrowded tank can trigger aggressive behavior. Be mindful of your fish's space and territorial requirements and of her relative need to dominate.

There may not be enough food, especially for the bigger fish. A big fish that does not get enough food may prey on his smaller tankmates. Make sure all your fish get sufficient food.

If you have chosen a good mix of species to live together harmoniously, provided them the right amount of space and given them sufficient food, you are well on your way to making a peaceful fish community.