Butterfly Goodeid

The butterfly goodeid is the most commonly kept species in the aquarium from the family Goodeidae, which is endemic to Mexico. Goodeids are also livebearers, but in a very different way from guppies and platies: the fry are nourished directly inside the mother through umbilical-cord-like extensions (trophotaeniae) and are born large. The male is a showy, deep-bodied fish whose scales shimmer blue–green, with a black band and a bright yellow edge on its tail.

Its natural habitat is confined to a few springs and streams; water extraction, pollution and invasive species have made it endangered. Aquarium-bred stock forms an important backup for the conservation of the species; for this reason care should be taken not to hybridize it with other species.

It lives in the spring pools and streams of the upper Ameca River in the state of Jalisco in western Mexico. These waters are clear, moderately hard and planted; they cool noticeably in winter and warm up in summer.

• Volume: at least 120 liters and a 100 cm tank length for a group of 6–8.
• Water: 22–25°C is ideal; it tolerates short periods of cooler water. pH 7–8, moderately hard water.
• Layout: plenty of swimming space, with tough-leaved plants along the edges. It may nibble soft, fine-leaved plants.
• Maintenance: it eats a lot and produces a lot of waste; a strong filter and a 30% water change every week.

A plant-leaning omnivore. Spirulina flakes and granules, blanched spinach and peas should be the staple. It also eagerly eats frozen brine shrimp, bloodworms and daphnia. It has a big appetite; feeding small amounts frequently reduces aggression and water pollution.

An active, lively species. Males display to each other and chase females. Its tendency to nip long, slow fins is well known; it increases especially when food is scarce.

Good companions: other goodeids (species it does not hybridize with), swordtails, large platies, barbs suited to hard water, Ancistrus plecos.

Avoid: guppies, bettas, angelfish and long-finned varieties; dwarf shrimp; very small and slow fish.

It is kept in a group, not singly: at least 5–6 individuals, 2 females per male. In a large group the males' aggression is spread out and displays are seen more often. When kept in small numbers the dominant male wears out the others and the females.

A livebearer. The male and female mate briefly face to face. Gestation lasts about 8 weeks; the female gives birth to around 5–30 large (1.5–2 cm) fry. Remnants of the trophotaeniae may be visible on the fry's bellies; these disappear within a day or two. Adults usually do not chase the fry, and the fry eat crushed flakes and brine shrimp from day one.

Hardy. Columnaris and fin rot can appear in soft, dirty water. Fin-nipping wounds are common in newcomers and in cramped aquariums; keeping a large group in a spacious aquarium is the best prevention.

Males have a black band and yellow edge on the tail, and their bodies are brighter and deeper. Males have no gonopodium; the front rays of the anal fin are shortened and separated by a notch (andropodium). Females are larger, spotted and plainer in color, with no yellow edge on the tail.