Spotted blue-eye rainbowfish (Pseudomugil gertrudae), Gertrude's rainbow

The spotted blue-eye rainbowfish (Pseudomugil gertrudae), also known as Gertrude's rainbow or the spotted blue-eye, is a tiny, peaceful freshwater nano fish native to Northern Australia, Papua New Guinea, and Indonesia.

Growing to only 1.2 to 1.5 inches (3 to 3.8 cm), they feature striking iridescent blue eyes, translucent fins marked with delicate black spots, and a shimmery silvery-yellow body. 

Tank Requirements & Water Parameters

Tank Size: Minimum of 10 gallons (approx. 40 liters), heavily planted with dense vegetation and dark substrate to make their colors pop.

Water Conditions: Temperature 24–28°C (75–82°F),

pH 5.5 to 7.5, preferring soft, clean water.

Behavior: Active shoaling fish, they must be kept in groups of at least 8 to 10 to reduce stress and show natural behavior.

They are also known jumpers, so a tight-fitting lid is essential.

Tank Mates: Peaceful with other nano fish (like tiny tetras or rasboras) and safe with adult dwarf shrimp.

Diet & FeedingOmnivores: They accept high-quality crushed flakes and micro-pellets, but thrive when supplemented with live or frozen foods like baby brine shrimp and daphnia.