Parkinson's Rainbowfish

Parkinson's Rainbowfish (Melanotaenia parkinsoni), also known as the Orange Rainbowfish, is a freshwater fish in the family Melanotaeniidae, endemic to river systems around Milne Bay in the eastern part of Papua New Guinea, including the Kemp Welch River. Described by Gerald Allen in 1980, it is among the larger and more robust members of the Melanotaenia genus. The species is well known in the aquarium hobby for the striking two-toned coloration developed by mature males. In the wild, it remains an important representative of New Guinea's highly diverse rainbowfish fauna, which has diversified extensively across the island's many isolated river drainages.

Parkinson's Rainbowfish is a large, muscular rainbowfish, with males reaching up to about 15 cm.

• Body: deep and robust, more muscular than many other Melanotaenia species
• Male coloration: bluish-silver front half transitioning to reflective golden-orange across the rear body and fins
• Fins: two dorsal fins, with males showing extended fin rays
• Females: comparatively duller and more uniformly silvery
• Tail: forked, edged in orange in mature males Its large size, muscular build, and distinctive front-to-back color transition in males distinguish it from most other Melanotaenia species, which more typically show uniform striping or spotting.

This species is native to river systems in the Milne Bay area of eastern Papua New Guinea, including the Kemp Welch River drainage. It inhabits warm tropical lowland rivers and streams, typically favoring areas with moderate flow and some vegetative or structural cover. As with many New Guinea rainbowfish, its range is tied to a specific set of river systems rather than being widespread across the island, reflecting the strong geographic diversification seen within the genus. Water conditions in its native range remain warm year-round, consistent with the equatorial lowland climate of the region.

Parkinson's Rainbowfish is a schooling species that naturally shoals in groups within rivers and streams, a social structure that also affords protection from predators. It feeds omnivorously on small invertebrates, algae, and other organic material found in the water column and along the substrate. During breeding, males intensify their orange coloration and extend their fins in display to attract females; eggs are scattered among vegetation or structure and receive no parental care after fertilization. As a larger-bodied rainbowfish, it occupies a somewhat higher position in the local food web compared to smaller relatives, while still serving as prey for larger fish.