Female molly fish have a small anal fin below their bellies and males have a modified fin that looks like a short stick. Males also tend to be smaller than females.Know More
Mollies are a live-bearing fish that make an interesting addition to the aquarium. Fish owners who want to breed mollies will need a male and female pair, who hopefully like one another. There are a few different varieties of mollies, but owners can always tell the gender of each molly by checking out their anatomy.
The male molly has a special fin called a gonopodium that is used for fertilizing the female molly. The gonopodium is a modified anal fin that looks like a narrow stick or straw. It may also feature a small section of normal fin tissue. The female molly has a half-moon-shaped anal fin in the same spot as the male sex organ. The sexual organs are fully identifiable at three months of age. This makes it easy to see at a glance if a fish is male or female.
There are a few other gender indicators that owners can look too. Females tend to be larger than males, but males will stay small if placed in a crowded tank. A pregnant female will display a large, tight belly that looks slightly squared as she gets closer to giving birth.Learn more about Aquatic Pets
According to Practical Fishkeeping, the first sign of pregnancy is that the fish's belly enlarges and appears rounder. Pregnant fish also exhibit a black spot on the belly called a gravid mark. As the pregnancy progresses, the fish's belly becomes very large and distended, and the gravid mark becomes larger and more obvious.Full Answer >
A Dalmatian molly is a fish that is a hybrid color variation of the sailfin molly. It gets its name because its color is similar to that of a Dalmatian dog: white with black spots.Full Answer >
For live-bearing fish, the pregnancy length depends on the species of fish and varies considerably. For instance, according to the MCH Portal, platies have a gestation period of up to 7 weeks. On the other hand, mollies have pregnancies of about 4 weeks, according to Fish Lore.Full Answer >
To tell if a black molly fish is pregnant, look for swelling and a black pregnancy mark on its lower belly. Black molly fish are almost always pregnant, meaning the pregnancy mark is almost always there.Full Answer >