The Fly River Rainbowfish was scientifically described by Munro in 1964. Its scientific name is Melanotaenia sexlineata. The species was first collected from a tributary of the upper Fly River by Lt. Stuart Campbelli in 1937.

Description
The Fly River Rainbowfish can exceed 7 cm (2.8 inches) in length. The body colour varies from bronze with a greenish tint to a golden shade of yellow. Between each row of scales, there is a thin blackish stripe. The body is also adorned with a prominent black marking right behind the upper pectoral fin base.

Geographical distribution, habitat and conservation
The Fly River Rainbowfish lives in streams in the south-western part of Papua New Guinea. The area is far from thoroughly surveyed and it is therefore impossible to know exactly how large the geographical range of this species is. The Fly River Rainbowfish has been found in a few places in the upper Fly River system near the port town Kiunga. Kiunga is located roughly 830 km (516 miles) upstream from the sea.

The typical Fly River Rainbowfish habitat consists of small creeks surrounded by flat lowland rainforest. These streams have slow-flowing water that is clear but tea-coloured. The ground consists of clay on top of limestone.  

Keeping Fly River Rainbowfish in aquariums
The Fly River Rainbowfish adapts well to a life in captivity and does not need much space to thrive. If you know how to keep the water quality up in small aquariums, a 35 L (9 gallon) aquarium is large enough to house a group of five fishes. Try to mimic the natural environment of the Fly River Rainbowfish when you set up the aquarium. Floating plants are known to be appreciated since they protect the fish against harsh aquarium lights. In the wild, the Fly River Rainbowfish is used to being shadowed by the surrounding rainforest.

The Fly River Rainbowfish is used to acidic conditions from the wild but is known to tolerate neutral and even slightly alkaline conditions in the aquarium. Its natural pH-range is 6.1-6.5, but it can tolerate a pH-value up to 7.5.

The Fly River Rainbowfish is an omnivorous species that needs both vegetable/algae-based food and meaty food in the aquarium. You can for instance combine flakes for herbivores/omnivores with regular servings of live foods such as insect larvae and brine shrimp. This type of live food is easily cultivated at home.

The Fly River Rainbowfish is listed as “Data deficient” in the IUCN Red List of Threatened Species.

Breeding Fly River Rainbowfish
Getting your Fly River Rainbowfish to spawn in captivity is not very tricky. Keep them on a varied and nutritious diet and provide them with suitable spawning media, e.g. java moss or spawning mops. The female will normally release a few eggs each day. If you keep the water temperature within the recommended range, you can expect the eggs to hatch within 10 days. The fry are fairly small when they hatch (even compared to the fry of other rainbowfishes) but they can eat infusoria. After a while, they will be large enough to devour newly hatched brine shrimp and vinegar eels.

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Other New Guinea Rainbowfishes

Axelrods Rainbowfish
Bleher’s Rainbowfish
Bulolo Rainbowfish
Higlands Rainbowfish
Silver Rainbowfish
Barred Rainbowfish
Lorentz’s Rainbowfish
Sentani Rainbowfish
Red Rainbowfish
Spotted Rainbowfish
Sepik Rainbowfish
Tami River Rainbowfish
Ramu Rainbowfish
Lake Wanam Rainbowfish
Threadfin Rainbowfish
Northern Rainbowfish
Ayamaru Rainbowfish
Angfa Rainbowfish
Arfak Rainbowfish
Boeseman’s Rainbowfish
Corona Rainbowfish
Waigeo Rainbowfish
Serong Rainbowfish
Goldie River Rainbowfish
Lake Tebera  Rainbowfish
Irian Jaya Rainbowfish
Strickland Rainbowfish
Yapen Rainbowfish
Lake Kutubu Rainbowfish
McCulloch’s  Rainbowfish
Mayland’s Rainbowfish
Misool Rainbowfish
Mountain Rainbowfish
Ogilby’s Rainbowfish
Oktedi Rainbowfish
Parkinson’s Rainbowfish
Lake Kurumoi Rainbowfish
Pima River Rainbowfish
Dwarf Neon Rainbowfish
Red Striped Rainbowfish
Van Heurn’s  Rainbowfish