Green Swordtail Fish

The Green swordtail(Xiphophorus helleri), is native to Central America. It is commonly known as green swordtail owing to the olive green natural colour that it exhibits in wild populations in Central America. There are other species in the same genus referred to as ‘swordtails’ including variants such as marbled swordtail and Highland swordtail.

The green swordtail is a small-bodied colourful species which are popular aquarium fish. Swordtails are generally less than 80 mm in length but can grow up to 120 mm (Allen et al. 2002). Swordtails found in aquariums are usually orange in colour, however feral populations often take on a bronze or olive colour in natural waterways.

Green swordtails originate from Mexico and Belize, Central America. It is a member of the Poeciliidae family (livebearing toothcarps), which also includes the noxious fish. Gambusia holbrooki commonly referred to as gambusia - also known as ‘mosquito–fish’, and pest fish Xiphophorus maculatus also kown as the Platy fish.

Swordtails are highly variable in colour but are usually bright orange on both body and fins with alternating silver and orange lines along the trunk. Feral populations often take on a bronze or olive colour with an orange-red mid lateral stripe in natural waterways (McDowall 1996).

Like many small native species, the exotic green swordtail is omnivorous and consumes algae, detritus and small insects. The males are easily identified by the elongation of the lower part of the tail, whilst the females do not have a sword-like tail but a very angular dorsal fin (Allen et al. 2002). They are a live-bearing species and reproduce at a young age, producing several broods per year.

Green swordtails are a popular aquarium fish and feral populations are most likely the result of aquarists discarding unwanted specimens into waterways or escapees from ponds reaching waterways through flooding events.

There have been no studies on the impacts of green swordtails on aquatic ecosystems. However, swordtails are closely related to Gambusia holbrooki which can quickly establish large populations and out-compete native fish for habitat and food, so there are concerns regarding the potential impact of the green swordtails on native species and ecosystems in local waterways.

In Queensland, Australia it is believed that increasing populations of green swordtails have been associated with the decline of nine native fish species (Western Australia Fisheries 2003).

Some tips you can do related to the ornamental fish which considered as a Noxious fish species, eg. Gambusia holbrooki, be on the lookout for new species in your local waterways. Give unwanted aquarium fish to friends or a pet shop, rather than letting them go in the wild. If you are involved in fish stocking, obtain a fish stocking permit from relevant parties before buying fish for restocking.

Also, buy fingerlings from local suppliers rather than outside your region or interstate, to minimize the chances of introducing other species not native to your area. If you are a fish farmer, comply with aquaculture permit conditions designed to prevent the escape of fish (e.g. screened water outlets), and keep to your approved species list.

It is extremely difficult if not impossible to eradicate pest fish once they become established in the wild. It is therefore vital to prevent non-native species such as the Green swordtail, Platy fish, Gambusia holbrooki and other ornamental fish species from abroad who may unwittingly have a negative impact to your local waterways if mishandled.