New Guinea rainbowfish
Melanotaenia affinis
A vibrant, active rainbowfish from New Guinea's rainforests: the silver body lights up with blue, green and yellow hues that change with light and mood — a shimmering effect typical of Melanotaeniidae. Robust and adaptable thanks to the seasonal variability of its natural habitat. In schools of 6–8+ with dense plants and open swimming space, the chromatic displays of competing males are a daily spectacle. Fast, tireless swimmer: requires long tanks.
Water Temperature
22 - 28 °C
pH Value
7 - 8
Water type
Freshwater
Tank level
Surface and middle
Adult size
11 cm
Minimum tank volume
>= 120 L
Minimum group
>= 6
GH
5 - 15 dGH
KH
2 - 7 dKH
TDS
95 - 295 ppm
Conductivity
148 - 461 uS/cm
Species description
Geographical Origin and Habitat: New Guinea (Northern). Populates mountain streams, crystal clear rivers and rainforest pools both in lowland and foothill areas.
Taxonomy and Morphology: North New Guinea Rainbowfish (Melanotaenia affinis). Classic rainbowfish with a laterally highly compressed rhomboidal body (humped back in old males) and double contiguous dorsal fin.
Social Behavior: Lively and peaceful gregariousness (minimum 6-8 specimens). Moves in a school in the upper water column. Males engage in choreographic "sparring" (without physical damage) expanding their fins to visually dominate.
Coloration and Sexual Dimorphism: Extremely variable depending on the capture zone (morph "Pagwi", "Bundi"). Generally sports a dark olive body superiorly and yellow/gold inferiorly, cut by a dense lateral black band. Males much larger and more colorful than females.
Care, breeding and tankmates
Aquarium Setup: Minimum 100 cm (40 inches) aquarium. Loves open water for frantic swimming, therefore plant only along the back or side glass (Vallisneria is excellent). Strong current appreciated. Intense lighting will bring out the iridescent reflections.
Diet and Feeding: Surface insectivore. The mouth is upturned. Provide floating foods (very high quality flakes, freeze-dried) and live/frozen food (Daphnia, White mosquito larvae). Struggle to eat foods deposited on the bottom.
Water Quality: Very tolerant, but expresses itself best in slightly hard and neutral/alkaline waters. Requires excellent water quality through regular massive changes (very sensitive to high nitrates).
Compatibility and Cohabitation: The perfect community fish for Asian or Australian aquariums. Coexists very well with other Melanotaenia, Glossolepis, Loaches, and huge schools of Danios/Rasboras. Absolutely harmless.
Aquarium Breeding: Continuous Spawners. After a frantic courtship rite at dawn, they scatter adhesive eggs among the leaves of Java moss or synthetic mops. Parents will ignore the fry, which require infusoria and powdered food.
Risks and Diseases: Mycobacteriosis. All Melanotaenias, if exposed to prolonged nitrate spikes, can develop "Fish Tuberculosis" (Mycobacterium marinum): they lose colors, become emaciated and develop ulcers (Incurable).
Geographic Origin and Distribution
New Guinea (Northern). Populates mountain streams, crystal clear rivers and rainforest pools both in lowland and foothill areas.
Origin
Selective breeding and cultivarsAfrica and MadagascarSouth and Southeast AsiaAustralia, New Guinea, and OceaniaTropical oceans and reefs
Fish profile
- Temperament
- Peaceful
- Their temperament is generally peaceful. Males frequently spar playfully without causing harm. They add dynamic energy to community tanks.
- Diet
- Omnivore
- They are naturally omnivorous. They readily accept flakes and small frozen foods. A varied diet enhances their vibrant colors.
- Life expectancy
- 5-8 years
- The North New Guinea Rainbowfish typically has a lifespan of 5 to 8 years when kept in captivity under optimal care. Providing a stable aquarium environment with clean, well-oxygenated water is essential for maximizing their longevity. A balanced diet and maintaining them in a peaceful school also help reduce stress and prevent disease. Regular water changes are critical, as they are sensitive to accumulated nitrates and poor water conditions.
- Adult size
- 11 cm
- The catalog's scalar value is 11 cm. The FishBase SPECIES table (v25.04 snapshot) source reports a maximum adult measurement of 11.5 cm for this species, recorded as standard length (SL). The taxonomic record consulted is Melanotaenia affinis (v25.04); male or unsexed record. These figures are not interchangeable: the first is the profile's editorial reference, whereas the second is a published maximum under a specific measurement convention; differences among sources can reflect sex, population, life stage and measuring method.
- Sex ratio
- Harem
- Keep one male to multiple females. This significantly reduces male harassment. Multiple males can coexist in larger aquariums.
- Feeding frequency
- Twice daily
- Feed small portions twice a day. They consume food rapidly from the surface. Avoid overfeeding to maintain water quality.
- Bioload
- Medium
- They produce a moderate bioload. Efficient filtration is needed for their active lifestyle. Regular water changes maintain pristine conditions.
- Flow
- Strong
- They appreciate moderate to strong flow. This simulates their native river habitats. Good circulation is highly beneficial.
- Jump risk
- Yes
- There is a very high jump risk. A tight-fitting lid is absolutely essential. Many are lost to open tanks.
- Reproduction
- Oviparous
- They are prolific egg scatterers. Parents will eat eggs if not removed. Fry require extremely small initial foods.
- Compatibility & tankmates
- Verify
- They are peaceful but highly active. Avoid housing with slow or timid species. They thrive with other energetic fish.
- Tank level
- Top/Middle
- They swim in the middle and upper levels. They require plenty of open swimming space. Perimeter plants provide security.
Scientific Parameters & Models
FishBase
Window to the official scientific data of the species
Data synced on: 06/15/2026
- Trophic level
- 2.9 ± 0.4 se
- Resilience
- Medium (1.4 - 4.4 years)
- Phylogenetic uniqueness (PD50)
- 0.5
- Bayesian Length-Weight
- a = 0.01122, b = 3.04
- VulnerabilityLow vulnerability (10 / 100)
Image gallery
Licensed images linked to the species or, when marked, to the closest representative taxon.
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