Keeping Male Swordtails Together

Several species of swordtail exist, with the most widely available species in the aquarium the green swordtail (Xiphophorus hellerii). Although not as dramatically belligerent as some fish, for example, male bettas, male swordfish are territorial and sometimes don̵7;t take kindly to competition, with the result being stressed fish and torn fins. It is, nevertheless, possible to keep more than one in a tank provided you take steps to make each male feel he has enough space and enough females.

  1. Background

    • Originating in the rivers of Central America, green swordtails are generally peaceful creatures, well suited to a community tank as they get along well with most other tropical freshwater fish. The only problem is the tendency of some, although not all, males to be highly territorial when you have more than one. They won̵7;t be aggressive toward other species or toward females of their own. Sexing adults is straightforward since males have the eponymous swords -- lengthy singular spikes on their tail fins -- while females don̵7;t.

    Tank Size and Gender Ratio

    • To keep multiple male swordfish, you need plenty of space. A well-planted 40- or 50-gallon tank is almost essential. If you have the space for a larger one, even better. Individual swordtails respond differently to social pressures, and some fish keepers even report successfully keeping all-male groups. Normally, however, you need at least three females per male to avoid fighting over mates, and the more females the better. For example, two or three male swordfish in a 50-gallon tank along with about 10 females should be fine.

    Unwanted Offspring

    • In a multi-gender setup, it's likely the swordtails will breed, which isn̵7;t necessarily a problem. The fish in a community tank will likely eat most of the fry and, if your tank is lightly stocked, the few survivors won̵7;t need new accommodation. If you want to ensure the survival of some of the fry and are certain you have the space or can find new homes for them once they mature, transfer some to a nursery tank.

    Emergency Action

    • If you have a small tank and a couple of male swordtails fighting hard, you̵7;ll need a bigger tank or to transfer one to a separate home. In a large tank, the problem might be sorted by adding females, although that's not guaranteed. In the meantime, separate the overly aggressive males with a tank partition, dividing the females equally between them.