Dwarf MacCulloch's Rainbow (Melanotaenia maccullochi)

The Dwarf MacCulloch's Rainbow (Melanotaenia maccullochi) packs everything people love about rainbowfish into a nano-friendly 3 inch package: constant motion, peaceful manners, and males that flash bronze, black-striped flanks with red-orange fins when the morning light hits the tank. It is one of the easiest rainbowfish to keep and one of the smallest, which makes it a perfect step up for a planted community. Browse the rest of our freshwater livestock while you are here.

Care Guide

Rainbowfish are undemanding as long as they get the two things every schooler needs: numbers and swimming room.

• Tank size: 20 gallons or larger, with more length than height. A lid is smart, rainbowfish are enthusiastic jumpers when they spar.
• School size: Keep 6 or more, with a mix of males and females if you can. The males color up hardest when they have someone to show off for.
• Water: 70 to 79°F, pH 6.0 to 7.5, soft to moderately hard. Very adaptable once acclimated, it just wants clean, stable water.
• Setup: Densely planted edges and background with an open lane down the front. Dark substrate and morning light show the colors best.
• Diet: An easy omnivore with a small mouth. Crushed flakes or small pellets as the staple, plus frozen daphnia, baby brine, and bloodworms for conditioning.

Specifications

Tank Mates & Compatibility

A model community fish. It shines alongside other active, similar-sized schoolers like Odessa barbs, larger tetras, rasboras, corydoras, and plecos, plus nerite snails on cleanup duty. Males spar with each other in harmless flashing displays and ignore everyone else. Skip long-finned slowpokes only if your school is too small to keep the energy inside the group, and avoid dwarf shrimp, which fit in a rainbowfish mouth.

Recommended Foods & Supplies

• Xtreme small floating pellets, a krill-first staple sized right for its small mouth
• Frozen daphnia and baby brine shrimp from our freezer for color conditioning
• Seachem Flourish Tabs for the planted tank it looks best in
• Browse all freshwater livestock and supplies

FAQ

Why does it look plain in the bag?
Rainbowfish color is mood and light driven. A stressed, newly bagged fish goes silvery. Give it a planted tank, a proper school, and a week of good food, and the bronze body, dark stripes, and red-orange fins come out.

How many should I get?
Six minimum, more is better. This is a true schooling fish, and both its confidence and the males' color depend on the group.

Will it outgrow my tank?
No. This is one of the smallest rainbowfish, topping out around 3 inches, which is why it works in a 20 gallon where the big rainbows do not.

Is it really a beginner fish?
Yes. It is hardy, adaptable to a wide range of water, eats everything, and lives 3 to 5 years with basic care.