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Care guide · Freshwater · fish

McCulloch's rainbowfish

Melanotaenia maccullochi

McCulloch's rainbowfish (Melanotaenia maccullochi)
Photo: Jesse de Vries / iNaturalist, CC BY 4.0. Photo: Jesse de Vries / iNaturalist · Source · CC BY 4.0Resized and compressed; no cropping or colour changes.

McCulloch's rainbowfish (Melanotaenia maccullochi) is a small, active rainbowfish from the coastal waters of northeastern Queensland. Its slender body has dark horizontal stripes, and mature males may show colourful fins. Despite its modest length, it is a social shoaling fish that needs room to swim and display. The older collective label “dwarf rainbowfish” is not always taxonomically precise: related forms were separated as distinct species after modern research. Check the scientific name and, when possible, the provenance of aquarium fish.

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At a glance

Temperature
20–30 °C
pH
5.5–8.0
GH
8–15 °dGH
Aquarium length
At least 60 cm
Minimum aquarium volume
At least 54 L
Adult size
Up to 7 cm
Group size
At least 6 individuals
Temperament
Peaceful

About this species

The accepted scientific name is Melanotaenia maccullochi Ogilby, 1915, family Melanotaeniidae. It is named for Australian ichthyologist Allan Riverstone McCulloch. Fishes of Australia describes a silvery to yellowish fish with six to eight dark horizontal stripes; colour intensity varies geographically. Adult males are usually more colourful and have longer fins than females. The species remains small: sources report about 6–7 cm standard length. This measures from the snout to the base of the tail fin, not total length.

Natural habitat

Under the current species boundaries, M. maccullochi occurs in coastal waters of northeastern Queensland, between Cape Flattery and the Cardwell region. Fishes of Australia records small clear creeks and Pandanus swamps with abundant cover from aquatic plants and woody debris. Seriously Fish also describes a wider range of habitats, from flowing creeks to still tannin-stained pools; older information about the species complex may include taxa now separated. Do not turn such local observations into one universal aquarium recipe. Genetic and morphological work led to M. sahulensis and M. wilsoni being described as separate species.

Aquarium and layout

Seriously Fish gives a minimum footprint of 60 × 30 cm and about 54 litres for a 60 × 30 × 30 cm tank. This is the geometric capacity of those dimensions, not a guarantee that every layout or larger group will fit. Keep at least six conspecifics, preferably six to eight or more when space allows. A calm, planted aquarium with wood, cover and open gaps lets the fish swim and display. The specialist source recommends slow flow and clean water. Use a secure lid, as active rainbowfish may jump.

Water conditions

The Seriously Fish profile lists 20–30 °C, pH 5.5–8 and GH 8–15 dGH, noting that pH varies by collection locality. FishBase reports field values of 24–30 °C and pH 5.5–7 from particular habitat references. These observations and the broad profile range are not a reason to make aquarium conditions fluctuate. Keep temperature and water quality stable, mature an appropriate filter and acclimate fish with their provenance and prior conditions in mind. GH is not KH; the consulted species sources do not give a specific aquarium target for KH.

Behaviour and group size

McCulloch’s rainbowfish is peaceful but can be skittish. A group of at least six to eight conspecifics supports normal social behaviour and colour display. Males show more strongly in the presence of their own species. Seriously Fish suggests broad groups of similarly sized fish, but this guide does not present individual combinations as guaranteed. Natural co-occurrence with another species is also not, by itself, proof of safe aquarium compatibility. Do not house small or slow companions solely because water values overlap; consider size, behaviour and swimming space.

Feeding

The species is omnivorous and, according to Seriously Fish, accepts a range of dried, frozen and live foods. Offer complete dry food the small fish can take readily and vary it with suitably fine animal foods. Existing complete flakes are linked as one component of a varied diet. Dried daphnia is an occasional supplement, not a staple. Distribute small portions so less dominant fish can feed, and remove leftovers to protect water quality. Live or frozen food adds variety, but no single product is a complete diet.

Breeding

This rainbowfish scatters eggs. Females may lay about 150–200 adhesive eggs, which attach to aquatic plants or a spawning mop. A separate breeding aquarium with fine-leaved plants or a synthetic mop makes the eggs and fry easier to monitor. Seriously Fish describes slightly harder, alkaline water around pH 7.5 and about 26.5–29 °C for directed breeding; these are breeding conditions, not routine aquarium targets. Eggs hatch in roughly 7–12 days, depending on temperature. Newly hatched fry are tiny and initially need very fine food. Adults provide no dependable parental care, so check the spawning material regularly.

Sources & review

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

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