Tropical Fish Compatibility

What is Tropical Fish Compatibility and Why is it Important?


 Tropical fish compatibility is the term aquarium hobbyists use to describe the ability of a species of fish to get along with other species. Some species of fish are naturally more aggressive than others while some have a temperament peaceful enough that they can be kept with virtually any other species of fish. If you want to maintain peace in your aquarium, you will need to select species of fish that can get along with each other. There are two ways you can go about selecting compatible fish for your tank. You can either pick a species you want to keep then research the compatible tank mates, or you can select species from fish from the various grouping of aquarium fish based on their compatibility.

Categories of Compatibility

When it comes to compatibility, freshwater aquarium fish are generally divided into three groups: community, semi-aggressive and aggressive species. Community fish are those which are typically peaceful in nature and which thrive best in groups with their own species or other community fish. Semi-aggressive fish are often larger than community fish and the males of the species tend to become somewhat aggressive in regard to territory and breeding. Many of the largest species of freshwater fish belong to the category of aggressive species and some of them are best kept singly or in tanks with only one or two other fish. In order to ensure that the fish in your tank get along it is wise to avoid mixing aggressive and community fish. Semi-aggressive fish, on the other hand, can be kept with community fish as long as there are no other males to compete for territory and the fish are provided with plenty of space and hiding places.

Species Based on Compatibility


Community Fish – Many of the smaller species of freshwater aquarium fish belong to the community category because they do not tend to show any aggression toward other fishes. Guppies, swordtails, mollies, platies, danios and tetras are some of the most popular fish belonging to this category. Bottom feeders such as corydoras and otocinclus catfish can also be considered community fish. Most community fish are also schooling or shoaling species which means that they thrive best in groups with several of their own species. Though most community fish are even-tempered, some species such as tetras have a tendency to nip at the fins of other fish – this behaviour can be controlled by keeping the fish in large schools.

Semi-Aggressive Fish – This category of fish includes gouramis, eels, sharks, barbs and loaches. These species tend to grow larger than most community species of fish and with their increased size comes heightened aggression. Most semi-aggressive species of fish can be kept with others of their own species or with community fish as long as certain conditions are met. Male gouramis in particular should not be kept in the same tank with other males of the same species. When a male gourami feels that another male is encroaching upon his territory or infringing upon his breeding rights, he may attack the other male until it backs off or dies. If you choose to mix semi-aggressive fish with community fish be sure to provide your community with fish plenty of hiding places and try to avoid any major size differences between the fish to prevent the community fish from becoming prey to the semi-aggressive fish.


Aggressive Fish – The main species belonging to the aggressive category of freshwater fishes are cichlids. There are believed to be around 2000 species of cichlid in existence, though only about 1,300 have been identified. While some smaller cichlids can get along with community or semi-aggressive fish, large cichlids such as African cichlids and Oscars should be kept alone or in a species tank. Because many of the fish belonging to this category have specific tank requirements, aggressive fish are generally not recommended for novice aquarium hobbyists. Another factor contributing to the difficulty of keeping aggressive fish is that because many of them are very large, they require large tanks. Oscars, for example, can grow up to 18 inches in length and require a tank capacity of at least 55 gallons.