Common Molly Fish (Mollienesia or Poecilia sphenops)

Mollenesia or Molly fish are an adaptable fish and live well within the fish community. Though they prefer a little salt with their water, they can live in fresh water or salt water aquariums. Molly fish can be found normally where fresh water meets salt water in various regions of the world.


Life Expectancy

Short fin Molly fish live on average 4 to 5 years. They can grow to five inches if their environment is just right. They need an aquarium of at least 15 to 20 gallons. But don’t cramp them. It is far better to have one male and maybe two or three females than a lot of fish. More than one male will cause fighting, especially if they are both colorful. The “alpha” male is determined by the one with the prettiest colors, so getting two males that are similar in color is not going to be good for one of the males.

Water and Lights

So now you know what size tank and that you need to add a little salt, how about the water’s temperature? Most authorities say to keep the tank between 75° to 80° Fahrenheit (24° to 27° Celsius). Since Molly Fish like a little salt with their water, by adding ½ teaspoon of marine aquarium salt to every gallon of water, you will make your Molly fish very happy.

Keeping the aquarium light on or turning it off? I suppose that will be your choice. I just have to think that in the wild, the Molly’s can’t turn the sun on or off and they manage quite well.

Molly Fish Food

Molly fish thrive on vegetable flake food combined with either live or dried blackworms or bloodworms. They also like their vegetables! Not to worry, they will eat the algae on the sides of the aquarium to get their recommended daily allowance. However, if there aren’t a lot of algae for them, then you will need to subsidize their diet. You can do this with either a vegetable based flake or you can simply boil some peas, spinach or cucumber (no seasoning please!), smash them up until it is a creamy texture and drop in tiny amounts (no more than the size of a pea).

Molly Fish Roommates

Short fin Molly fish live well with species that are not too flamboyant. Authorities’ say they live well with Angel fish, however, I have found that the Molly seems intrigued (or maybe jealous) with the flowing tail of the Angel fish. If you place an Angel fish in the tank, you stand a chance that the Molly will nip at its fins until it causes an infection on the Angel fish. However, Molly fish live harmoniously with larger Tetras such as Silver Tips and Black Skirts. They also are good with Swordtails, Platy fish, and Catfish. They do get along with Plecos fish, but, if you add a Plecos fish, place only one. These guys don’t like competition. Since they also like their algae, they may not leave very much for the Molly fish to eat.

Giving Birth

Molly fish do not lay eggs. Instead, the “fry” grows inside the mother until they are large enough for her to give birth. A few days before you suspect that she is will give birth you need to separate her from the other fish in the aquarium. There are clear “birthing” bins that you can place her in. Make sure you give her vegetation in the bin with her. The bin sits inside the same tank, with the same water, but it keeps the other fish from dining on her newborns.

A female Molly fish can give birth from 10 to 140 little Molly Fish (and sometimes more). Once she is finished giving birth, you need to immediately take her out of the birthing bin and place her back in the general population, leaving the little ones safe in the bin to grow and flourish.

Molly Fish   Updated: July 4, 2019
avatar Hey, I'm Fabian, chief editor at Aquarium Nexus. I really enjoy the aquarium hobby and love sharing my experience with others. If you have any questions feel free to contact me or leave a comment below.

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