Breeding Mollies

Breeding Mollies

[Tropical Molly]

This page is about the tropical molly with more than just breeding information. Enjoy some useful caring for your molly. We also provide information on tank selection and care, and information on tropical fish diseases.

Directory > Breeding Mollies

Mollies are found in the wild of Mexico and Central America. They were first found by Valenciennes in 1846. Since then, they have been bred intensely and there are many different varieties in wide range of sizes, colors, body and fin types. Mollies are hardy and undemanding. They are easy to raise and breed. The Molly is a peaceful active fish but, at times prefer to hover under plants, ornaments and rocks in the aquarium. Mollies are essentially non-aggressive and do well in a community tank with other non-aggressive pet fish. They can be kept in a single species aquarium. Different strains of Mollies should not be mixed in the same aquarium if someone is raising them for purebred strains. Male and female of different strains and characteristics will inter-breed. The resulting offspring will be a genetic mix of the two. Different strains should be kept in separate tanks if someone is trying to maintain a pure bred genetic true line of Mollies.

The natural habitat of Mollies are slow moving streams and ponds. They are live bearers and a long toothed carp. Water temperature should be kept at seventy to eighty degrees F. They like hard water (100-150 mg per liter). They are a brackish fish and need one teaspoon of sea salt per one gallon of water up to one cup of sea salt per 10 gallons of water to thrive. The water should be alkaline and kept at a pH of 7.5. Plants should be planted and not only for the Mollies to nibble on but, to provide cover for the young to escape. Mollies are live bearers and are cannibalistic in that, they will eat their young. Adult Mollies should be kept separate from the young. It is advised that the pregnant female be placed in a holding tank and, be closely observed so that removing her from that tank when the young ones are born, can be easily accomplished. Different kinds of breeding traps are available at pet stores for the protection of the young Mollies. Plants should be planted only around the edges of the tank because mollies love to swim. A loose cover of floating plants is good. Water-Sprite and Spirulina are recommended. The substrate (gravel) should be dark in color.

The gestation period of a Molly is 24-48 days and is usually dependent upon the temperature of the water. First broods are small of about 15 offspring. Broods increase in number with each successive brood to number up to 150 per brood as the female grows larger. The larger the female, the larger the number of young ones that she will have born. Size of the female, when adult, is about 3 inches long, while the male adult is a bit smaller. The males reproduction organ is called the gonopodium. The gonopodium is a modified anal fin. The females anal fin is rounded where the males gonopodium is long and tubular. The gonopodium allows internal fertilization of the eggs inside the female Molly. The gonopodium is an organ of copulation and when mating, this is inserted into the female where some of the sperm fertilizes the eggs. The rest of the sperm is deposited and stored in the folds of the female fish ovarian tubes. Females kept alone after being bred once, will continue to have successive broods of offspring. Utilizing the sperm stored in her ovarian tubes, she may give birth six to nine times in her life. Each successive brood will be even larger than the previous one. The young grow as eggs inside the female and then, they break out of the egg during birth as live and free swimming fish. This protects the young from egg eating predators until born. The pregnant female Molly can readily be detected of sexual gender because she will have a dark mark in the front of her anal fin. This is called the gravid spot and it becomes quite noticeable as she approaches giving birth.

Genetic breeding is difficult because after the first breeding, the female retains that sperm for the rest of her life. If a desired male is selected for breeding with a previously bred female, the offspring that result will be mixed with the genetic characteristics of all previous mates. The majority of the offspring may carry the genes of the most recent breeding. Females, for this purpose should be separated from males at the earliest time in their life before mating occurs. Young males can be recognized by their distinctive gonopodium which appears at about three or four weeks of age. Males and females should be transferred to separate tanks. Mollies become sexually active from about three months of age on.

The Mollies diet should be varied and should consist of dried prepared foods plus, small live foods such as brine shrimp, bloodworms, and tubifex worms.

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