Spotted Blue-Eye Rainbowfish (Pseudomugil gertrudae)

Pseudomugil gertrudae, known as Gertrude's Blue-Eye or the Spotted Blue-Eye Rainbowfish, is one of the most captivating nano fish in the aquarium hobby. Native to slow-moving waterways, swamps, and forest streams of New Guinea and northern Australia, males display iridescent blue and yellow spotted patterning on a translucent body, with elaborate paired dorsal fins and vivid blue eyes — a remarkable amount of beauty packed into a 3–4 cm fish.

Males engage in constant, gentle sparring and display behavior — spreading their fins and shimmering to attract females and deter rival males. This behavior is harmless and makes them particularly entertaining to observe in a species-appropriate nano setup. Females are more subdued but still attractive.

This is a specialized nano species that requires attention to water quality and diet. Like all Pseudomugil, they prefer gentle flow, soft to moderately hard water, and heavily planted environments with floating plants and fine-leafed vegetation. They attach eggs to plant surfaces or spawning mops.

Gertrude's Blue-Eyes are best kept as a species or in nano community tanks with other tiny, gentle fish. They are sensitive to water quality degradation and should not be kept in tanks with competing or aggressive species.

Water Parameters: pH 6.0–7.5, temperature 22–28°C, GH 4–15. Gentle flow, stable parameters, and regular small water changes are important. Avoid strong current. Slightly soft, slightly acidic water preferred; adapts to neutral moderately hard conditions.

Tank Setup: 30–40 liter nano tank for a group of 6–10. Dense vegetation with Java moss, fine-leafed plants, floating plants. Dark substrate. Gentle sponge filtration. Provide spawning mops or fine plants for egg deposition. Secure lid recommended.

Feeding: Micro flake, micro pellets, baby brine shrimp, micro worms, daphnia. Feed twice daily in tiny amounts. Variety enhances coloration and spawning behavior.

Tankmates: Only with other tiny peaceful nano fish and dwarf shrimp. Any active, larger, or competitive species will stress them. Best as a species tank or paired with Boraras microrasboras or similar.

Breeding: Egg-scatterers that deposit eggs on fine plants and mops. Separate eggs for best fry survival. Tiny fry require infusoria initially, then micro-brine shrimp nauplii.