Gertrude's Blue-Eye Rainbowfish
Pseudomugil gertrudae
Min Tank Size
40L
Adult Size
3.5 cm
Lifespan
3 years
School Size
6+
About
Native to slow-moving, heavily vegetated waters across northern Australia and New Guinea, Pseudomugil gertrudae is one of the most visually striking fish you can put in a nano tank. Males are the showstoppers here. They carry spotted, translucent bodies, vivid electric blue eyes, and long extended rays on their dorsal and pectoral fins that flutter like flags when they display. Females are plainer but share that gorgeous eye color.
5 cm they're genuinely tiny, so everything about their care revolves around protecting that delicacy. These fish thrive in soft, slightly acidic to neutral water, and a blackwater setup with tannins from Indian almond leaves or driftwood really brings out their best coloration. Temperatures anywhere between 22 and 28 degrees suit them, though stability matters far more than hitting a specific number.
Diet is where beginners sometimes struggle. Gertrudae blue-eyes are obligate carnivores with tiny mouths. They ignore most dry foods initially and need live or frozen micro foods like baby brine shrimp, daphnia, or micro worms to thrive and show full color. Once conditioned they can accept quality micro-pellets or crushed flake, but live food should stay a regular part of the rotation.
In a well-planted tank with gentle flow and dim lighting, these fish become remarkably bold and spend most of their time mid-column displaying to each other. If you want to see what this species actually looks like at its best, searching community tank builds featuring Pseudomugil gertrudae is well worth your time.
Water Parameters
Temperature
°CpH
GH
dGHKH
dKHSwimming Level
Flow Preference
Keeping multiple Gertrude's Blue-Eye Rainbowfish together
Gertrude's Blue-Eye Rainbowfish are shoaling fish and need company of their own kind. Keep a group of at least 6. Smaller groups leave them stressed, washed-out in color, and prone to hiding.
Compatibility
Best kept with other small, gentle species from soft water biotopes. Dwarf rasboras like Boraras brigittae or Boraras maculatus are a natural pairing, as are small Corydoras species on the bottom. Pygmy corydoras work especially well. Cherry shrimp adults are generally fine, but newly born shrimp fry are absolutely small enough to be eaten, so factor that in if you're trying to maintain a breeding shrimp colony. Avoid anything nippy, tiger barbs and even serpae tetras will shred those elaborate fin extensions quickly. Also avoid larger, boisterous fish that outcompete them at feeding time.
Commonly kept with
Species this one is most often paired withCommonly tried but avoid
Often paired, but shouldn't beCare Notes
The biggest mistake beginners make is underfeeding or offering the wrong food. These fish have tiny mouths and high metabolisms. Flake crumbled between your fingers is a starting point but live baby brine shrimp or micro worms are genuinely necessary for good health and color. Water quality failures hit them fast given their sensitivity, so a cycled, well-maintained tank is non-negotiable. Many people also house them with species that are too large or too active, which stresses them into hiding and refusing food.
Behavior & Aggression
Males are mildly territorial with each other, especially during spawning displays. Two males in a small space will spar repeatedly, flaring fins and chasing, which can stress subordinate fish if there's no line of sight break. This rarely escalates to actual injury, and in a tank with decent planting you can keep multiple males without problems. They show zero interest in harassing other species. The main concern is the reverse: these fish are so small and their fins so delicate that they can easily become targets if the wrong tankmates are chosen.
Things to Know
- Tiny enough to predate on newly born dwarf shrimp fry
- Very sensitive to poor water quality, do not skip maintenance
- Males display aggressively to each other but rarely cause injury
- Lid required, they jump when startled
- Do not house with any fin nippers, elaborate fins are easy targets
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