Aggressive saltwater fish come in a variety of shapes, sizes and aggressive traits. Some fish are more aggressive over space or food. Do your research before adding any fish or even purchasing your aquarium to make sure it is a suitable home for the fish you desire.
Signs of Fish Aggression
Even after you plan and take precautions, how do you know if your fish are getting along?
Depending on your species, this most outward sign of aggression can be over territory, mating or 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 if they are injured. You can attempt to reintroduce the aggressor to the tank after serving some time in your hospital tank.
In a well setup tank, all fish will have equal access to food at feeding time. Some species may be slower or more reluctant than others, but they should still make an appearance. If you haven't seen certain fish for more than a few days or actively see one fish consistently take food away from another fish, you may need to rethink your tank or feeding strategy. Small fish that are stealing food out from the operculum of larger fish may be causing additional stress.
Although this behavior may be harder to see if you do not watch your tank other than at feeding time, this behavior is a clear marker of aggressive fish. Usually, it occurs when one less-aggressive fish starts to make their way out of their cave. Another more aggressive fish will then swim quickly directly at the other fish and force them back into their cave. This may happen multiple times in a row. A fish that is unable to leave their home, even if they can get some food, will get stressed and sick.
Depending on how your species breeds could set off another aggressive behavior. Some fish might try to steal the eggs while over-protective parents might exponentially expand their territory. If breeding is not your goal, try to keep fish as one of each species or non-breeding pairs.
01 of 07
Clown Triggerfish (Balistoides conspicillum)
The Clown Triggerfish can grow very large (more than 1 foot and six inches) and requires over 300 gallons for just them. They are vicious nibblers and will decimate any live rock, hard coral and invertebrates they can get their beak wrapped around. They are aggressive fish that require roommates of similar large size and mentality.
02 of 07
Blue & Gold Damselfish (Pomacentrus coelestis)
Many damselfish are known for fiercely defending their territory and the Blue & Gold Damselfish is no exception. Although they do not need a lot of water volume for their small size, 30 gallons at bare minimum, these fish will aggressively attack any fish that approach their cave. They have been known to bite their human caretakers if they clean too close to them.
03 of 07
Blue Line Grouper (Cephalopholis formosa)
The Blue Line Grouper is a smaller member of the monstrous grouper family, and require a mere 250 gallons minimum for one fish. Given their large mouth and big appetite, these fish are frequent munchers on smaller tank fish and crustaceans. It is recommended to only keep fish with the Blue Line Grouper that cannot fit into their gaping mouths! Crustaceans can be kept if they have tight hiding places the grouper cannot maneuver.
04 of 07
Goldbar Wrasse (Thalassoma hebraicum)
With a distinctive gold bar behind the operculum of mature males, the Goldbar Wrasse is a bright addition to a saltwater tank. Requiring 125 gallons minimum, their aggressive traits appear when new fish are added to their established tank. Once established in their territory, the Goldbar Wrasse will attack any new occupants. In order to mitigate this trait, this fish should be the last addition to your tank, so all other fish can establish their territories first.Continue to 5 of 7 below.
05 of 07
Coral Hogfish (Bodianus mesothorax)
Also known as the Eclipse Hogfish or Mesothorax Hogfish, these fish transition from pale pink and black with yellow spots as juveniles, to striking maroon face, black mid-body band and yellow body as adults. They can grow up to eight inches and require 70 gallons per fish. They are beneficial to have in a tank since they will clean parasites off larger fish. However, smaller fish will be bullied and reefs will be nibbled until decimated.
06 of 07
Banded Hawkfish (Cirrhitops fasciatus)
Don't let their small size fool you, the Banded Hawkfish is an aggressive tankmate. Also known as the Redbar or Blood Red Hawkfish, these fish have a bright coloration and minimal tank requirements of 30 gallons. However, they require a tank with fish larger than themselves, since they will eat any smaller inhabitants along with crustaceans.
07 of 07
Jeweled Moray Eel (Muraena lentiginosa)
As with all moray eels, these fish have not one, but two pairs of jaws. Behind their front teeth is a pharyngeal jaw, also with teeth, that pulls trapped food deeper into their mouth. Although not known for attacking humans, if an eel feels threatened, it will bite!
Since the Jeweled Moray is a smaller eel, it is better suited to smaller aquariums, at least 50 gallons in size. Eels are also escape artists, so make sure your tank has a well-seated lid. Being nocturnal predators, eels will ambush fish and crustaceans in the night, but can be taught to feed during daylight hours.
Of these examples, many fish within the above family groups (wrasses, grouper, eels, etc) have similar aggressive tendencies. It is strongly recommended that prior to adding an aggressive species to your tank that you research their environmental needs and plan appropriately.
If it's too late to pre-plan, here are some methods to limit fish aggression:
- Add your most aggressive fish to the tank last. This will allow more timid fish to find a good spot to hide and establish their territory.
- Don't host breeding pairs of fish. Some breeding fish parents turn deadly in the pursuit to protect their developing young.
- Add additional hiding spots for shy fish to take refuge. Keep an eye out for the charging behavior described above.
- When feeding, disperse the food throughout the aquarium. If all the fish aren't competing in the same small area, it will allow less aggression over food.