Murray River Rainbowfish

The Murray River Rainbowfish (Melanotaenia fluviatilis) is a freshwater species in the family Melanotaeniidae, native to the Murray-Darling river basin in southeastern Australia, one of the continent's largest river systems. It is closely related to the Crimson-spotted Rainbowfish and the broader Eastern Rainbowfish complex, with which its taxonomy has historically overlapped. The species is a familiar sight in the lowland rivers, billabongs, and wetlands of the Murray-Darling basin and remains widespread and common within its native range. It is popular in the freshwater aquarium trade owing to its peaceful nature and shimmering coloration, contributing to its recognition beyond its native distribution.

Murray River Rainbowfish reach roughly 8-10 cm and share the classic rainbowfish body plan.

• Body: elongated, laterally compressed, moderately arched in males
• Coloration: silvery-blue base with faint pink to reddish horizontal stripes along the sides
• Fins: yellow to orange dorsal, anal, and caudal fins, more vivid in breeding males
• Dorsal fins: two, separate
• Tail: forked Compared with the Crimson-spotted Rainbowfish, it tends to show less intense red spotting and a more streamlined, less deep body, with color and stripe intensity often used alongside locality to separate the two closely related species.

This species occurs throughout the Murray-Darling river basin of southeastern Australia, inhabiting lowland rivers, billabongs, backwaters, and wetlands with slow to moderate flow. It favors areas with aquatic vegetation, submerged timber, and undercut banks that provide cover and feeding opportunities. Murray River Rainbowfish tolerate a range of water temperatures across seasons, from cooler winter conditions to warm summer lowland waters, and can persist in both flowing river channels and more static billabong habitats. Water clarity in its range varies from clear to turbid depending on season and flow conditions.

Murray River Rainbowfish are schooling fish, typically moving in loose aggregations through open water and along vegetated margins. They feed during the day on small aquatic invertebrates, insect larvae, algae, and organic material, foraging both in the water column and near the surface. Spawning occurs in warmer months, when males intensify their coloration and court females near fine aquatic vegetation; adhesive eggs are scattered among plants and left unguarded. As a widespread and abundant species, it forms an important part of the food web in the Murray-Darling system, both as a consumer of invertebrates and as prey for larger native fish and birds.