The Green Swordtail (Xiphophorus hellerii) – species freshwater / brackish fish. It is native to an area of North and Central America stretching from Veracruz, Mexico, to northwestern Honduras.
Natural populations are found in various types of habitat from sea level to around 1500 m altitude, including fast-flowing, rocky streams, springs, ditches, ponds, and rivers containing clear to turbid water. In most cases, the water is less than 1.5 m deep and there is no aquatic vegetation.
In flowing, water adults tend to congregate in areas with greater current, while juveniles and subadults display a preference for quiet marginal zones. Introduced populations may occur in springs, streams, rivers, canals, ditches, pools, artificial reservoirs, and other environments, and the species exhibits a degree of tolerance to polluted conditions.
The male Green Swordtail grows to a maximum overall length of 14 centimetres and the female to 16 centimetres. The name «swordtail» is derived from the elongated lower lobe of the male’s caudal fin. Sexual dimorphism is moderate, with the female being larger than the male, but lacking the «sword». The wild form is olive green in colour, with a red or brown lateral stripe and speckles on the and, sometimes, caudal fins. The male’s «sword» is yellow, edged in black below. Captive breeding has produced many colour varieties, including black, red, and many patterns thereof, for the aquarium hobby.
An aquarium with surface dimensions of 120 x 30 cm or equivalent should be the smallest considered.
Choice of décor is not especially critical though it tends to look best in a heavily planted set-up with a dark substrate. Wild forms should also suit an aquarium arranged to resemble a flowing stream with water-worn rocks and small boulders. The addition of some floating plants and driftwood roots or branches to diffuse the light entering the tank also seems to be appreciated and adds a more natural feel. Filtration does not need to be particularly strong though it does seem to appreciate a degree of water movement.
Stomach analyses of wild specimens have shown it to be a generalised omnivore, feeding on a range of aquatic and terrestrial invertebrates, organic detritus, algae, and other plant material. The aquarium is unfussy and will accept just about anything offered. Offer a balanced diet comprising good quality dried products along with small live and frozen foods such as Daphnia, Artemia, and chironomid larvae (bloodworm).
In confined spaces groups of males tend to form dominance hierarchies and may invest a significant proportion of time maintaining their respective positions.