Butterfly splitfin

The butterfly splitfin comes from clear, spring-fed streams in western Mexico, where aquatic plants grow thickly and the water runs well-oxygenated and hard. Males reach about 8 cm and carry bright reflective scales along their flanks, edged in black and yellow on the tail, while females are plainer and slightly larger. Unlike the common guppy or molly, this goodeid does not store sperm — females must be re-fertilised for each brood, and gestation runs about 55–60 days before she releases a handful of very large fry. Those fry are born big enough to eat adult food immediately and the parents rarely bother them. A group of five or more works best; males establish a pecking order through display and light chasing but serious damage is rare. The tank needs at least 80 litres with good filtration and moderate flow, since these fish are messy feeders and sensitive to deteriorating water. They are omnivorous with a strong taste for algae, so include spirulina flake or blanched spinach in the rotation alongside regular prepared foods. pH should be in the 7.0 to 8.0 range and temperatures between 20°C and 26°C suit them year-round, reflecting the hard, alkaline water of their native springs. Dark substrate and dense planting bring out the males' best colour. Though sometimes labelled extinct in the wild, small populations still persist in the Ameca and Sayula basins, and the species has a solid captive population in the hobby.