How to Keep Fry Population Down in an Aquarium

Occasionally the fry population in your aquarium community can grow so large you will need to control their numbers. Fry are the babies, or guppies, of any fish species. Large fry populations can occur when the aquarium features too many fish unwilling to eat the fry, though many fish species will eat their own fry. If you are looking to control your fry population, use fry-eating fish as well as other simple methods of control.

  1. Manual Removal

    • Manual removal is an option should you choose to sell your guppy fry to a local pet store. Use your aquarium net to remove them from the tank. Place them in a fish bowl or small, portable tank that is filled with water. If necessary, have a friend or family member hold the bowl or tank while you drive the fry to your local pet shop. It is also a good idea to call pet shops in your area to find out if they purchase fry or are willing to exchange the fry for store credit.

    Plant Removal

    • Fry will stay within the confines of tank plants to avoid being eaten by other members of your aquarium. Moving a group of plants can result in the discovery of a whole population of fry you didn't know were in your aquarium. Removing some of the plants, at least temporarily, will expose the fry to other fish in the tank and can help control the fry population.

    Zebrafish Method

    • Zebrafish are recommended for fry population control as they eat fish smaller than themselves. They grow to about 2.4 inches and are easily identifiable due to the blue strips that run the entire length of their bodies. Known as "feared hunters" in the aquarium world, there are several varieties of zebrafish in existence, including stripped or speckled versions. Long- and short-finned versions are also options as are different-colored varieties, such as albino or green zebrafish. Though they will eat fry, zebrafish will not bother other fish in your aquarium that are the same size or larger. They can also live in almost any aquarium setting, making them an ideal choice for controlling your fry population. Use one to five zebrafish at a time depending on the severity of your fry population issue.

    Additional Recommended Fish

    • Other fish recommended for keeping a fry population under control include angelfish, which come in a variety of bright colors and sizes. Because some species can grow quite large, it is best to use them if you have a sizable tank, such as a 75 gallon tank. They are aggressive with most other fish including their own species, though aggression level varies depending on specie type. Use them if your tank features other aggressive species, such as tangs, eels, and hawkfish.
      Varieties of tetrazona fish, such as black widow and black skirt tetras, are recommended for controlling mollie, swordtail and platy fry populations. Tetras feature vertical black strips on the sides of their bodies with bright orange fins. Because tetras only grow to about 2.8 inches, you can use four or five of them at a time to control fry populations. Though tetras can usually coexist with more docile fish species, they are not recommended in combination with long, flowing fin varieties of fish.