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Care guide · Freshwater · fish

Goldbreast splitfin

Ilyodon furcidens

Pair of goldbreast splitfins (Ilyodon furcidens)
Pair of goldbreast splitfins. Photo: Andrewbogott, CC BY-SA 3.0. Photo: Andrewbogott · Source · CC BY-SA 3.0Proportional resizing through existing media pipeline; no crop or colour alteration.

The goldbreast splitfin (Ilyodon furcidens) is an active Mexican goodeid from rivers and streams. In the wild it mainly grazes algae and aufwuchs, while also taking insects from the surface and small invertebrates. It needs more swimming room, current and oxygen than a typical warm-water community fish. The specialist Goodeid Working Group recommends a spacious, low-profile aquarium of at least 120 litres. Keep temperatures on the cool side, offer varied foods, and choose captive-bred fish whose provenance is as well documented as possible. Plan for an active fish that needs room and consistent, well-filtered conditions.

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At a glance

Temperature
18–24 °C
pH
7.0–8.0
GH
10–20 °dGH
Aquarium length
At least 75 cm
Minimum aquarium volume
At least 120 L
Adult size
Up to 10.3 cm
Group size
At least 6 individuals
Temperament
Peaceful

About this species

Ilyodon furcidens (Jordan & Gilbert, 1882) belongs to the family Goodeidae. It was originally described as Characodon furcidens; historical combinations include Ilyodon paraguayense and Ilyodon xantusi. Taxonomy within Ilyodon is complex: feeding forms and populations vary, and the Goodeid Working Group includes some historical xantusi forms within I. furcidens. This guide follows the accepted species name but does not merge I. whitei or I. cortesae into it. The name refers to the forked teeth.

Natural habitat

The species occurs in western Mexico in several river basins in Jalisco and Colima, including the Ameca, Armería, Marabasco and Salado. Habitats include pools and riffles in streams and rivers over sand, gravel, stones and bedrock. Current ranges from still to swift; adults often use more flowing areas, while young fish can also occur in sheltered pools near the bank. The Goodeid Working Group reports local declines and disappearances where water levels shrink and non-native fish spread.

Aquarium and layout

The Goodeid Working Group recommends at least 120 litres and a generous footprint; Seriously Fish gives a 75 × 30 cm base. Treat these as a lower limit for an active group, not an ideal final size. Use rounded gravel and smooth rocks, roots or branches, edge planting and open swimming lanes. Moderate to swift current and very oxygen-rich water are important; the specialist group gives at least 8 mg/L dissolved oxygen. Regular substantial water changes help maintain water quality, but avoid abrupt shifts in temperature or chemistry.

Water conditions

Seriously Fish gives 18–24°C, pH 7.0–8.0 and GH 10–20 dGH. FishBase lists a warmer 24–27°C environmental range, while the Goodeid Working Group warns that sustained temperatures above 26°C may harm health. For aquarium care we therefore follow the specialist aquarium range of 18–24°C and avoid prolonged heat. Stable, clean, oxygen-rich conditions matter more than rapidly correcting the tank toward one exact number.

Behaviour and group size

Goldbreast splitfins are often found in large schools in the wild. Six or more is reported as a practical starting group; this is not an experimentally established biological minimum. The fish are usually peaceful toward robust species that tolerate cooler temperatures and current. Males display and may squabble, although serious injury is not often reported. A species aquarium makes it easier to observe natural behaviour and preserve locality lines. Assess any tankmates by adult size, activity, current and food competition as well as water values.

Feeding

In nature the species mainly eats algae and aufwuchs, along with surface insects and small invertebrates. The Goodeid Working Group describes different mouth forms with different emphasis on grazing or surface feeding; both can use aufwuchs. Offer a varied omnivore diet: complete flakes or fine granules, algae-rich plant foods, blanched vegetables and suitable small frozen or live prey such as Daphnia and brine-shrimp nauplii. Remove leftovers and do not rely exclusively on animal protein.

Breeding

Ilyodon furcidens is livebearing. Embryos develop within the female and the fry are born relatively well developed. The Goodeid Working Group records young mainly from February to July, possibly later. It reports that fry are usually not eaten, although dense plants provide extra refuge. Keep population history documented: Ilyodon has taxonomic and geographic uncertainties. Do not mix fish of unknown origin or label a locality line unless its provenance is supported.

Sources & review

This care guide draws on several specialist sources and was last checked on .

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