The Japen (or Yapen) Rainbowfish is a rare and striking schooling species endemic to Yapen Island in Papua, Indonesia. Like most rainbowfish, they are active swimmers that display their best colors in established aquariums with high water quality and plenty of horizontal swimming space. They are sexually dimorphic and thrive in slightly alkaline, moderately hard water.
Japen Rainbowfish At a Glance
Japen Rainbowfish Tank Requirements
Will Japen Rainbowfish fit in your tank?
Care guides tell you what Japen Rainbowfish needs, the next question is whether your tank can safely provide it. Test Japen Rainbowfish against your tank size, maintenance needs, and the fish you already keep before you buy.
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Japen Rainbowfish Water Parameters
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Japen Rainbowfish Temperament & Compatibility
Japen Rainbowfish Varieties
Each variety inherits the species defaults above. Only differences are highlighted.
Male
Males are deeper-bodied and feature striking mauve coloration with red-orange horizontal stripes and brightly colored fins (red-orange dorsal, anal, and caudal fins). They will constantly display to attract females and establish hierarchy.
Same care requirements as the base species
Also known as: Adult Male, Show Male
Female
Females are more slender and noticeably less colorful than males, generally showing a subdued silvery body with translucent fins. Keeping multiple females per male helps disperse mating harassment.
Differs in 1 trait from base species
Also known as: Adult Female, Unsexed
Japen Rainbowfish Care Guide Summary
The Japen Rainbowfish, scientifically known as Melanotaenia japenensis, belongs to the Rainbowfish family group. Adults reach a maximum size of approximately 11 cm and have a compressed body shape with a moderate growth rate. Classified as peaceful, this species primarily occupies the surface and mid-level zones of the aquarium and produces a low level of biological waste.
To thrive, the Japen Rainbowfish requires a freshwater only aquarium with a minimum volume of 110 litres and a tank length of at least 90 cm. Water temperature should be maintained between 24°C and 28°C, with a pH range of 7–8.2 and a general hardness of 5–15 dGH. A moderate water flow is preferred.
The Japen Rainbowfish is a rewarding species to keep, provided its core environmental needs are met. This species is available in 2 varieties: Male and Female. Each may differ slightly in size, temperament, or care needs, so it is worth checking the specific requirements of the variety you plan to keep.
Japen Rainbowfish Habitat Setup
When setting up an aquarium for the Japen Rainbowfish, a moderate water flow best suits their natural preferences. Because this species occupies the surface and mid-level zones, the aquarium layout should prioritise adequate surface area with floating cover to make them feel secure near the waterline and open swimming space in the centre of the tank for free movement. Useful additions include dense planting to provide cover, break sightlines, and reduce stress. Keepers should note that a tight-fitting lid is essential, as this species is a known jumper.
Japen Rainbowfish Compatibility Notes
Classified as peaceful, the Japen Rainbowfish is a schooling species that feels most secure in a sizeable group, where natural shoaling behaviour reduces stress and brings out their best colours. When choosing tankmates, their energetic swimming style may stress more sedentary or timid species. Selecting tankmates that favour different water layers from the surface and mid-level zones can help reduce competition and territorial overlap.
Japen Rainbowfish Recommended Tank Sizes
Standard aquarium sizes that meet the minimum volume and length requirements for Japen Rainbowfish.
30 Gallon Breeder
40 Gallon Breeder
55 Gallon Standard
60 Gallon Breeder
75 Gallon Standard
90 Gallon Standard
Show 10 more tank sizes
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Frequently Asked Questions About Japen Rainbowfish
How big does Japen Rainbowfish get?
Japen Rainbowfish (Melanotaenia japenensis) typically reaches a maximum adult size of approximately 11 cm. They have a compressed body shape and a moderate growth rate.
What tank size does Japen Rainbowfish need?
A minimum aquarium volume of 110 litres and a tank length of at least 90 cm are recommended for Japen Rainbowfish. This ensures enough swimming space and helps maintain stable water conditions.
What water parameters does Japen Rainbowfish need?
Japen Rainbowfish thrives in freshwater only conditions with a temperature range of 24–28°C, a pH between 7 and 8.2, and a general hardness of 5–15 dGH. A moderate water flow is preferred.
Is Japen Rainbowfish peaceful or aggressive?
Japen Rainbowfish is classified as peaceful with an aggression score of 2 out of 10. They are generally well-suited to peaceful community tanks.
How many Japen Rainbowfish should be kept together?
Japen Rainbowfish is a schooling species and should be kept in groups of at least 6. Larger groups help distribute aggression and encourage natural schooling behaviour.
Does Japen Rainbowfish have any special tank requirements?
Yes. Japen Rainbowfish benefits from plants - densely covered in the aquarium. These features help replicate their natural habitat and promote overall health and well-being.
Does Japen Rainbowfish need a lid on the tank?
Yes. Japen Rainbowfish is a known jumper, and a tight-fitting lid or cover is essential to prevent escape. Even a small gap can be enough for a determined fish to leap out.
Top Tank Mates for Japen Rainbowfish
These fish are strong compatibility matches for Japen Rainbowfish based on water preferences, temperament, adult size, and tank behavior.
Orange Delight Shrimp
Caridina loehae
Ideal Tank MatesMottled Loach
Paracanthocobitis botia
Ideal Tank MatesSchwartz's Cory
Corydoras schwartzi
Ideal Tank MatesLeopard Cory
Corydoras leopardus
Ideal Tank MatesGold Laser Cory
Corydoras sp. 'CW010'
Ideal Tank MatesDainty Cory (Salt and Pepper Cory)
Corydoras habrosus
Ideal Tank MatesPlants That Suit Japen Rainbowfish
These plants pair well with Japen Rainbowfish based on shared water preferences, layout fit, and how likely they are to hold up in the same aquarium.
Afzel's Anubias
Anubias afzelii
Amazon Sword
Echinodorus amazonicus
Anacharis
Egeria densa
Anubias Barteri
Anubias barteri
Baby Tears
Lindernia rotundifolia
Balansae
Cryptocoryne crispatula
Fish Similar to Japen Rainbowfish
Price's Rainbowfish
Chilatherina pricei
A rare, energetic, and beautiful species native to the Reifafeif River on Yapen Island, Indonesia. They form midwater aggregations in main river channels over rocks and boulders. Like most large rainbowfishes, they are rapid, continuous swimmers that require long aquariums with moderate to high water flow and pristine, oxygen-rich conditions.
Ajamaru Rainbowfish
Melanotaenia ajamaruensis
A highly active, schooling rainbowfish endemic to the Ayamaru Lakes in West Papua, Indonesia. Currently listed as Critically Endangered in the wild. It is closely related to Boeseman's Rainbowfish but possesses a notably more slender body and more prominent reddish-brown horizontal striping. They thrive in hard, alkaline water with dense vegetation and require significant horizontal swimming space.
Boeseman's Rainbowfish
Melanotaenia boesemani
An incredibly popular and active schooling fish endemic to the Ajamaru Lakes in West Papua, Indonesia (currently listed as Endangered in the wild by the IUCN due to overfishing and habitat loss, though commercially captive-bred). Famous for the mature male's spectacular blue and orange split-coloration. They require long tanks for active swimming, excellent oxygenation, and warm, hard, alkaline water to thrive.
Angfa Rainbowfish
Melanotaenia angfa
A beautiful and active schooling fish native to the Yakati River system in West Papua. Named in honor of the Australia New Guinea Fishes Association (ANGFA). Like many large rainbowfish, they are vigorous swimmers that require long aquariums to thrive. They display their best colors in well-planted tanks with clean, well-oxygenated water.
Batanta Rainbowfish
Melanotaenia batanta
A stunning, active shoaling fish endemic to Batanta Island in West Papua, Indonesia. They inhabit clear, moderately fast-flowing rainforest streams. Like most rainbowfish, they are highly social, energetic swimmers that require plenty of horizontal swimming space and clean, well-oxygenated water. Males exhibit striking blueish coloration with narrow orange stripes. The species is considered Vulnerable in the wild.
Grime Rainbowfish
Glossolepis dorityi
A rare and highly active schooling fish native to the Grime River system in New Guinea, currently listed as Critically Endangered in the wild. Widely known in the hobby as Dority's Rainbowfish, they are prized for the male's unique zigzag lateral striping. They are peaceful community fish that require spacious, well-oxygenated tanks with plenty of open swimming room.