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Swordtail fish are commonly available fish who can thrive in community aquariums. Swordtails come in colors including red, black, neon, pineapple and marigold. The males' long tail spikes give the fish their name, and males can be territoriality aggressive toward one another, especially when there is a female present.
As long as no females are present, males can harmoniously coexist in groups of six or more. The larger the numbers the better the chance you have of diffusing any potential aggression within the group, with no one fish bearing the brunt of another's bullying. Smaller numbers of swordtails may be able to coexist, depending upon the personalities and aggression level of each fish.
Males and Females
It is possible to keep multiple males and females together in the same tank provided you have a large aquarium, heavily planted and decorated to provide sufficient hiding places. Make sure your tank is at least 50 gallons and you provide two or three females for each male in the tank.