Green Swordtail

• It does not lay eggs: the female retains the embryos and gives birth to fully formed young that can swim straight away.
• The sword on the tail is no use for swimming: it is a sexual ornament, and the classic experiments with this fish showed that females prefer the males with the longest sword.
• Escapes and releases by aquarists have established it as an exotic species in rivers on every continent except Antarctica.
• It is a livebearer: the female gives birth to fully formed, free-swimming young, with no free egg stage.
• The sword-shaped tail belongs to the male alone, and it is a classic case in the study of sexual selection: females prefer it long even though it imposes a swimming cost on its bearer.
• Females can store sperm and produce several successive broods from a single mating.
• It has been introduced into numerous countries through aquarium releases and figures among the exotic species established on several islands and in several river basins.

Skeleton type

Vertebrate - internal bony skeleton (fish)

Habitat and environment

Fast-flowing streams, springs and rivers of Central America

Sexual maturity

10 months

Gestation / incubation

4-6 weeks of internal gestation

Sources consulted: https://es.wikipedia.org/wiki/Xiphophorus_hellerii