How to keep mollies

Written by s. a. holt
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A tank populated with mollies can be an impressive sight. The deep black colouration of the black molly and the tall dorsal fin of the sailfin molly make them unique additions to any aquarium. Mollies (Poeciliidae) are often recommended as a beginner fish for a community tank but this is misleading. Mollies do best when kept alone or with other mollies. They require the addition of sea salt to their water in order to thrive and can even live comfortably in a marine tank if slowly acclimated to the increased salinity. They are active swimmers that can sometimes nip the fins of slower moving fish. Common colours for mollies are velvety black, silver, greenish blue, spotted black and white and gold. Mollies are available in a number of body shapes from the deep-bodied balloon molly to the more narrow and delicate lyretail variety.

Skill level:
Moderately Easy

Things you need

  • Heated aquarium (10 gallon minimum)
  • Floating plants
  • Sea salt

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  1. 1

    Prepare a molly tank by setting the water temperature between 25 degrees C and 28.3 degrees C. Add a teaspoon of sea salt for every 2 1/2 gallons of water. Mollies prefer medium-hard alkaline water. They can grow to 4 inches, so avoid tanks smaller than 10 gallons.

  2. 2

    Add floating plants to the water, and cultivate algae by making sure the tank receives some bright indirect light each day.

  3. 3

    Select fish that are free of white spots and have clear, intact fins. Mollies are active swimmers and are alert and curious. Avoid sluggish fish that remain at the bottom of the tank.

  4. 4

    Acclimate the transport bag containing your mollies to the temperature of your aquarium water for a full 20 minutes before releasing them.

  5. 5

    Avoid feeding mollies for the first 12 hours after introducing them into a new aquarium.

  6. 6

    Feed mollies a diet of flaked food. If possible supplement dry food with fresh brine shrimp or mosquito larvae occasionally.

  7. 7

    Observe your new fish closely for the first couple of days to make sure they are settling in well.

Tips and warnings

  • Mollies are hardy and bear live young rather than laying eggs. They are less interested in eating their babies than guppies, but the young should still be removed to their own tank.
  • Choose male mollies if you don't want a population explosion (with the exception of sailfin mollies). Keeping males will ensure that your tank will not become overcrowded with baby and adolescent fish. Males can be recognised by their tubular anal fins.
  • If you don't think you have enough algae in your tank for your mollies to munch on, give them a small piece of a well-washed lettuce or spinach leaf every once in a while. Float the leaf on the surface of the water and remove any leftover bits after a few hours.
  • When keeping multiple males with females, males may become aggressive toward one another. If you observe bullying, remove the aggressive male, or remove the females from the tank.
  • Avoid keeping more than one male sailfin molly to a tank. Sailfin males are particularly aggressive and territorial with one another.

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