Fish Only & Aggressive Tanks - Reef Central Online Community

Don't simply dismiss fish that are aggressive, they may disrupt the peace in your tank
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The (Trichogaster trichopterus) is a very popular fish but is often reported to be too aggressive. All gouramis are territorial. They like to claim a section of the tank, usually near the surface at the edge of some plants, and defend it. Usually, this isn’t a problem. The blue gourami is usually tolerant of the other fish. So, keeping just one gourami (of any species) in a community helps them get along well with everyone.
Rainbow Shark. Really cool freshwater fish, but I suggest only putting it in 20+ gallon tanks with semi-aggressive tank mates. Fishometer: 8
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The only fish on the list that requires a tank larger than 3 feet. It is generally encouraged to keep them in groups as the male will perform colorful displays to the females in the tank. However, you will need to introduce the female first or introduce as a group. They do change genders like clown fish. They are one of lesser aggressive tank mates, so if you are going to keep them, make sure they are one of the first saltwater aquarium fish you put in your tank. They are known to be jumpers so a cover is recommended.

Honorable Mention - Chrysipera Genus of Damselfish

They do not make my top ten because some consideration needs to be made to ensure you have success with their more aggressive nature, but if you take the right steps they make the cut. You can check our article. Often mistaken for the otocinclus catfish, this algae eater can get big and somewhat aggressive with tank mates as it grows.
Photo provided by FlickrYou can never keep a fish tank totally stress-free, but by making smart choices you can keep aggression to a minimum. Good luck!
Photo provided by FlickrHe found that an increase in tank size and complexity can reduce harmful aggressive behaviors, and make for healthier fish at home.
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Aggression presents a problem that plagues both aquarists and the victimized fish. Many causes of aggression are sure to cause complications in the tank and can sometimes be rather hard to deal with.It is very important to know which fish species are aggressive and how to avoid disastrous combinations of keeping fish in the same tank resulting in the death of multiple fish.An overcrowded tank can cause goldfish to become more edgy and feel as if they have to compete for space. Check to make sure the water volume is sufficient to sustain the amount of fish in the tank. The general rule of thumb is 20 gallons of water for the first fish, then 10 gallons for each additional fish. If the tank is too small it would be in the fishes’ best interest to upgrade, both for their health and the aquarist’s nerves. Goldfish may also develop aggressive behavior when a new fish is introduced into the tank and disrupts the “balance” of the social hierarchy.If you try this and it’s still not working you could try pulling out the aggressor leaving them in a bucket with an aerator and a heater for six to eight hours. That should disorient them so when you put them in the tank sometimes they just happen to click in and get along with their existing tank mate. Or if you have the luxury of setting up another aquarium you can move the aggressor out into the other aquarium for a few days to a week, let the new fish get acclimated, let it start eating, let it develop territories, and then put the old fish in. Don’t add fish that are notoriously aggressive–if they have a reputation for being aggressive, leave them at your local fish store–damselfish and maroon clownfish are notoriously aggressive fish–don’t expect them to be mild-mannered in your tankYes Chinese algae eaters are very aggressive and can live with oscars, convicts, frontosa, red devil Cichlids, Texas Cichlids, you name it. When they get big they are very tough and mean fish that will kill non aggressive tank mates and eat them. They are catfish.