Breeding Swordtail

How to breed Xiphophorus hellerii: livebearer biology, the male's sword and gonopodium, sexing, brood production, recommended sex ratio and fry care.

Overview

The Swordtail (Xiphophorus hellerii) is a livebearer rated beginner-level for breeding and is described as one of the easiest fish for amateur aquarists to breed when both sexes are kept together in suitable conditions.

Sexing

The female is larger than the male but lacks the sword, the elongated extension on the lower tail fin that males develop. Males also possess a gonopodium, a modified anal fin used to impregnate the female. A dark gravid spot develops near the female's anal fin during later pregnancy.

Conditioning the Breeders

The presence of a well-developed male spurs the maturity of females while inhibiting the maturity of nearby juvenile males. A ratio of one male to three or four females is recommended so that individual females are not overly harassed.

Spawning Behavior & Birth

Swordtails are live-bearers that give birth to fully formed fry rather than laying eggs, the male fertilising the female internally with the gonopodium. Breeding occurs readily when proper tank conditions exist and both sexes are present, which is why the species is regarded as one of the easiest for amateur aquarists to breed. A dark gravid spot near the female's anal fin during later pregnancy signals an approaching birth.

Fry Care

Fry require shelter, as they will be eaten by other aquarium inhabitants if they cannot find cover. Dense planting or a separate grow-out container greatly improves the share of each brood that survives. The young reach sexual maturity at around three months of age, so successive generations can appear in quick succession.

Common Challenges

Predation of fry by tankmates is the main loss, so dense planting or a grow-out space is advisable. An unbalanced sex ratio can lead to excessive harassment of females, which is why a ratio of one male to three or four females is recommended; the presence of a well-developed male also spurs the maturity of females while inhibiting the maturity of nearby juvenile males.