livebearers

Livebearers are fish that give birth to live young rather than laying eggs. In the aquarium hobby, the best-known livebearers belong to the family Poeciliidae and include guppies (Poecilia reticulata), mollies (Poecilia spp.), platies (Xiphophorus maculatus and relatives), and swordtails (Xiphophorus hellerii). Males retain a modified anal fin called a gonopodium, used to transfer sperm to the female, who can store sperm and give birth to multiple broods from a single mating.

Reproduction occurs after internal fertilization, with females carrying developing offspring inside the uterus and giving birth to free-swimming fry. Gestation periods typically range from about four weeks to two months, depending on species and conditions. Because fry are small and many predators are present in tanks, many aquarists provide plant cover or separate fry from adults, and some breeders stagger or limit matings to control numbers.

Habitat and care: Most livebearers are native to Central and South America and the Caribbean. In aquariums they are generally hardy, adaptable to a range of warm freshwater conditions, and omnivorous, feeding on flakes, pellets, and live or frozen foods. They mature quickly, and males are often more brightly colored or have longer fins than females, which can be helpful for sexing.

Ecology and human relevance: Livebearers are popular for beginners and breeders due to their vigor and ease of keeping. Some species, notably mosquitofish (Gambusia spp.), have become invasive when released into non-native habitats. Responsible hobby practices include avoiding release into the wild and managing breeding to prevent unwanted population growth in home aquariums.