Yellowfin Rainbowfish

The Yellowfin Rainbowfish (Melanotaenia flavipinnis) is a small freshwater rainbowfish in the family Melanotaeniidae, restricted in the wild to forest streams on Misool Island, part of the Raja Ampat archipelago in West Papua, Indonesia. It was formally described in 2012 and is one of the more geographically isolated species within the diverse Melanotaenia genus, which comprises dozens of species distributed across Australia and New Guinea. Its limited island range makes it of particular interest for freshwater biogeography, illustrating how rainbowfish species have diversified across isolated river systems. It is a smaller-bodied, less commonly documented species compared to its mainland New Guinea and Australian relatives.

Yellowfin Rainbowfish are small, slender-bodied fish reaching about 6-8 cm.

• Body: elongated and moderately compressed, less deep-bodied than many Melanotaenia relatives
• Coloration: silvery-olive to pale golden base with a faint horizontal stripe along the midline
• Fins: distinctly bright yellow dorsal, anal, and caudal fins, giving the species its common name
• Dorsal fins: two separate dorsal fins typical of the genus
• Tail: forked, yellow-tinged The vivid yellow finnage, especially in mature males, separates it from most other Melanotaenia species, which more commonly show red, orange, or blue fin tones.

This species is confined to clear forest streams and small tributaries on Misool Island in the Raja Ampat Islands of West Papua, Indonesia. It occupies shaded, tannin-influenced or clear freshwater with moderate flow, often among leaf litter, submerged roots, and overhanging vegetation typical of tropical island stream systems. Water temperatures in its native range stay warm year-round, consistent with equatorial lowland forest conditions. Because it is restricted to a single island's drainage network, its total range is naturally small compared to mainland rainbowfish species found across broad river systems in Australia and New Guinea.

Yellowfin Rainbowfish form loose schools in shaded stream pools and slower side-channels, moving through the water column to forage. They feed opportunistically on small aquatic and terrestrial invertebrates that fall into the stream, along with algae and fine plant matter, consistent with the omnivorous feeding habits typical of the genus. Reproduction follows the general rainbowfish pattern: males display brighter finnage to attract females, and eggs are scattered among fine plant roots or vegetation, adhering by short filaments, with no further parental care. As a small-bodied stream fish, it plays a role in the food web both as an invertebrate predator and as prey for larger aquatic and semi-aquatic predators.