Avoiding Aggression in Saltwater Fish

Aggressive saltwater fish come in a variety of shapes, sizes and aggressive traits. Some fish are more protective of territory; some are more inclined to fight over food. Do your research before adding a fish to your aquarium to make sure you're able to provide the environment needed to avoid injuries—or death—among your fish. Learn the signs of aggression and how to limit this behavior in seven fish that are notorious troublemakers.

Signs of Fish Aggression

Are your fish getting along? Watch for these signs of trouble in your tank that may need to be addressed to prevent stress, injury, or fatal attacks.

Active Attack: Among some species, including those in the wrasse family, conflicts commonly involve breeding territory and preferred hiding spots. You will see one fish actively biting or ramming into another fish. This dispute needs to be handled quickly by removing the aggressor or the victim, especially if they are already injured. You can attempt reintroduction after a few days, but the conflict may continue.

Feeding Behavior: In a well designed tank of adequate size to house its fish population, all fish have equal access to food at feeding time. If you notice that certain fish are hiding during feeding time or that one fish consistently takes food away from other fish, you may need to reduce your population or just remove particularly problematic fish. Large fish aren't the only culprits; small fish that steal food from the operculum (gill covers) of larger fish may be causing stress, too.

Charging: While less likely to cause acute injury than active attacking, charging creates insidious stress. It occurs when a seclusive fish attempts to leave its shelter, and a more aggressive fish forcefully swims toward it so that it retreats back into its hiding place. If this happens regularly, and the seclusive fish is unable to leave its home, it will become stressed and sick.

Breeding: Some fish aggressively defend their nests, eggs, and young; others aggressively try to eat others' offspring. These situations are stressful and can result in injured or dead fish. If breeding is not your goal, it's easier to keep one fish of each species or non-breeding pairs.

Limiting Fish Aggression

Many fish from the family groups listed below have similar aggressive tendencies. It is strongly recommended that you research the environmental needs of any aggressive species you'd like to add to your aquarium prior to purchasing it.

In general, you can help limit fish aggression with a few simple steps:

• Add your most aggressive fish to the tank last. This will allow more timid fish to find hiding spots and establish their territory.
• Don't keep breeding pairs of fish. Some breeding fish parents turn deadly in defense of their developing young. Fish eggs and young will also encourage aggressive feeding behavior from other species, creating conflict and stress.
• Add additional hiding spots where shy fish can take refuge.
• When feeding, disperse the food throughout the aquarium to allow well-spaced feeding and discourage aggression over food.

7 Aggressive Species

The following fish are beautiful but potentially troublesome additions to an aquarium. Knowing their individual space requirements and behavioral tendencies can help you incorporate them into your aquatic environment, if possible, or avoid these aggressive fish altogether.