Forktail rainbowfish
Pseudomugil furcatus
easy careOverview
The forktail rainbowfish (Pseudomugil furcatus), also called the forktail blue-eye, is a small, sparkling gem from the coastal streams of Papua New Guinea. Males are the show: yellow-and-black edged fins that they flick and spread constantly, and the bright blue eye typical of the Pseudomugil genus. At only 4–5 cm it’s a true nano fish, yet it has all the flash of the larger rainbowfishes. Colour deepens as the fish mature, so be patient with young stock.
Tank & water
Give a group a minimum of 60 litres (15 gallons) with plenty of open swimming space above the plants. They are active, so length matters more than height.
- Mature tank only: these fish resent instability. Always cycle the tank fully and let it settle before stocking.
- Water: they like neutral to hard, slightly alkaline water (pH 7.0–8.0). Very soft, acidic water is not their preference.
- Gentle flow and a lid: a well-baffled filter keeps them happy, and a cover stops surface-dwelling rainbows from jumping.
- Planting: fine-leaved plants and some floating cover frame their colours and give fry a chance.
Feeding
A micropredator by nature, the forktail has a tiny mouth and needs small foods. Offer quality micro-pellets and small flakes from the fish food range, and supplement heavily with live and frozen daphnia, cyclops, grindal worms and baby brine shrimp. Varied feeding is the single biggest lever on their colour and finnage.
Tankmates
Peaceful and non-nippy, forktails suit a calm community of other small, gentle fish — pygmy corydoras, small rasboras, otocinclus and shrimp all work. Avoid boisterous or large tankmates that will outcompete them at feeding time or intimidate this shy shoaler. Keep them in a group of six or more so males have rivals to display to.
For a bigger, mixed rainbowfish display, pair them with more open water and see our best large aquarium picks.
Common mistakes to avoid
- Adding them to an immature, uncycled tank
- Keeping too few — singles fade and hide
- Foods too large for their small mouths
- Boisterous tankmates that bully them off food
Forktail rainbowfish — frequently asked questions
How many forktail rainbowfish should I keep?
At least six, and ideally more. They are a shoaling species that colours up and displays best in a group, where males flare their yellow-edged fins at one another. A single fish or a pair will look washed out and stressed.
Are forktail rainbowfish hard to keep?
No — they are one of the easier blue-eye rainbowfishes, tolerant of a range of hard, neutral-to-alkaline water. The main rule is to add them only to a mature, cycled tank, as they dislike unstable conditions and the ammonia spikes of a new setup.
What do forktail rainbowfish eat?
They are micropredators with small mouths. Feed small floating flakes, micro-pellets and plenty of tiny live or frozen foods such as daphnia, cyclops and baby brine shrimp to bring out their colour.
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