Banded Rainbowfish

The Banded Rainbowfish (Melanotaenia trifasciata) is a freshwater species native to rocky streams and rivers of Cape York Peninsula in northeastern Australia, part of the rainbowfish family Melanotaeniidae. It is notable for extreme color variability between isolated populations, with individuals ranging from blue-and-yellow to deep red-striped forms depending on the specific stream or gorge they inhabit, a pattern of local adaptation that has made it popular among rainbowfish enthusiasts and researchers of color variation. Despite this variability, the species as a whole is not considered broadly threatened due to its distribution across numerous river systems. It belongs to the order Atheriniformes.

Banded Rainbowfish are moderately elongated, laterally compressed fish reaching 8-11 cm.

• Body: base color varies by population from blue to yellow to red, typically overlaid with two to three dark horizontal stripes
• Fins: yellow to orange, with two closely spaced dorsal fins
• Tail: deeply forked
• Stripe pattern is the most consistent identifying feature across otherwise highly variable color forms Because coloration differs so much between stream populations, the presence of the characteristic dark horizontal banding, rather than overall body color, is the most reliable way to identify this species and separate it from other Melanotaenia relatives.

Banded Rainbowfish are found in rocky, often clear-flowing streams, gorges, and rivers across Cape York Peninsula in far northeastern Queensland, Australia. They favor moderately flowing water over rock and gravel substrates, often in isolated headwater systems separated by rugged terrain, which has driven the species' notable population-level color variation. Water is generally warm (22-30°C) and well-oxygenated in these tropical stream habitats. The species tends to occupy pools and slower runs adjacent to rockier, faster sections, using boulders and overhanging vegetation for shelter. Its distribution across many separate, often isolated drainages has allowed distinct localized color forms to develop within the same species.

Banded Rainbowfish form active shoals in pools and slower stream sections, foraging during the day on aquatic insects, small crustaceans, algae, and plant material dislodged by current. Males intensify their stripe and body coloration during courtship, performing fin displays to attract females and establish loose dominance among rivals, generally without serious aggression. Spawning occurs repeatedly through warmer months, with females depositing adhesive eggs among rocks, roots, or vegetation; no parental care is provided afterward. Fry hatch within about a week and begin feeding on small invertebrates and algae. As an abundant stream-dwelling omnivore, the species plays a role in invertebrate population control and serves as prey for larger fish and birds in these Cape York waterways.