Dark-edged Splitfin Care Guide - Aquarium Setup, Diet & Breeding

The Dark-edged Splitfin is a small, unusual livebearer from the goodeid family. Its elongated body is generally olive, grey or yellow-brown, with subtle dark markings and a noticeably darker margin along the fins. Males are usually slimmer and more strongly marked, while females grow larger and have a fuller body shape.

Dark-edged Splitfins are endemic to the highlands of central Mexico, particularly parts of the Valley of Mexico and nearby Lerma River drainage. They inhabit cool freshwater springs, streams, canals, ponds and vegetated lake margins, although wild populations have been severely reduced by habitat loss and introduced fish.

A group should be housed in an aquarium of at least 60 litres, with a footprint around 60 by 30 cm or larger. Use a mature, well-filtered setup with gentle to moderate water movement, open swimming space and dense planting around the edges, including fine-leaved plants for shelter. A fine gravel or sand substrate, smooth stones, driftwood and some floating cover create a natural-looking environment while leaving room for grazing and courtship.

Females reach about 7 cm (2.8 inches), while males are usually smaller at approximately 5 cm (2 inches).

This omnivorous species naturally browses on algae, soft plant material and small aquatic invertebrates. Offer a varied diet based on quality flake or small pellets, supplemented with spirulina or other vegetable foods and regular portions of baby brine shrimp, daphnia, mosquito larvae or other small frozen or live foods. Variety is particularly important for maintaining colour, condition and successful reproduction.

Dark-edged Splitfins are best kept with peaceful, similarly sized cool-water fish that will not outcompete them for food or harass their fins. Suitable companions may include peaceful Mexican livebearers and other compatible, non-aggressive goodeids, provided there is no risk of hybridisation. Avoid large predators, fin-nippers, boisterous warm-water species and closely related fish with which they could crossbreed.

Dark-edged Splitfins are livebearers that reproduce through internal fertilisation rather than laying eggs. Keep a group with more females than males, and provide dense plants or spawning mops where young can shelter. Females give birth to relatively large, well-developed fry, which should be separated or heavily protected because adults may eat them. Feed the young finely crushed flakes, baby brine shrimp and other appropriately sized foods.

Females are larger, deeper-bodied and often less intensely marked than males. Males are smaller and slimmer, with more conspicuous colouration and a modified anal fin, known as an andropodium, used during internal fertilisation.