What Fish Can Live Together in an Aquarium?

Not all fish will live comfortably together. Large, predatory fish will eventually eat smaller tank mates and slow swimming fish become stressed in the company of boisterous, fast moving species. Many fish species are territorial and are threatened by other types of fish which resemble them, as fish which are similar normally require similar food and nest sites. Social fish species are not territorial and it is from these types that aquarists typically choose their community aquarium specimens.

  1. Size

    • Fish of the same size are best housed together. Predatory fish species frequently prey on smaller fish types, which is not possible when each specimen in the aquarium is the same size. Large predators of similar size will readily accept fresh, frozen or pellet food in the absence of living prey. The many different species of catfish grow to various sizes and the large plecostomus species will be suitable as tank mates for all of the fresh water large predators. Aquariums containing small to medium sized fish make for an interesting exhibit, as many individual fishes in this size range can be housed in the average home tank.

    Diet

    • Vegetarian species tend not to interfere with each other and make for good tank mates. The mainly plant and berry eating pacu from South America, blue sucker and various catfish species are well suited to be housed together. Many of these fish types will spread themselves out around the aquarium, as they graze on algae on the glass panes, driftwood, substrate and décor. Non-territorial species can be fed on a high quality commercial fish food, which makes meal times quick and simple. Danios, tetras and swordtails will all accept aquarium flakes.

    Behavior

    • Non-territorial fish are easy to keep together. These species are comfortable in the company of their own kind and in the presence of other fish types. Non-territorial species such as mollies, platys and guppies go well together. Territorial fish must be housed in a large aquarium and be offered many hiding spots and private retreats. Mixing mid-water and bottom dwelling species removes the element of competition and allows the aquarist to house a greater variety of fishes. Fish which look physically dissimilar are more compatible than those which exhibit similar shapes and colors as they can represent competition to each other.

    Water Parameters

    • Fish with similar water chemistry requirements are best housed together. Marine fish require sea water, while tropical fish which are found in rivers and lakes, must be housed in fresh water. Fish species such as South American cichlids, loaches and tetras, require soft water with a pH of less than 0.7, while fish types from hard water habitats, such as African cichlids, need to be kept in water with a pH above 0.7. Tropical fish types require warm water, in the region of 77 degrees Fahrenheit, while cold water species, such as goldfish, comets and sicklebacks prefer water temperatures below 75 degrees Fahrenheit.