If you’re searching for a tiny fish that truly stands out, look no further than Pseudomugil gertrudae, commonly known as the Blue-Eyed Rainbowfish. These nano fish are delicate, vibrant, and endlessly captivating, making them a favourite among hobbyists who appreciate small, peaceful species with plenty of character.
Appearance and Behaviour
Pseudomugil gertrudae are small, rarely exceeding 3.5 cm, but what they lack in size, they make up for in striking colouration. Males display brilliant blue eyes and shimmering stripes of silver, turquoise, and yellow along their bodies, while females are slightly less vivid but still beautifully patterned. They are peaceful schooling fish, thriving in groups of six or more, and their coordinated swimming adds dynamic movement to any tank.
Tank Requirements
Despite their delicate appearance, Pseudomugil gertrudae are hardy when kept in stable conditions. They prefer slightly acidic to neutral water (pH 6.0–7.0), soft to moderately hard water (GH 5–12 dGH), and temperatures around 22–26°C. They are ideal for planted tanks with gentle water flow, which mimics their natural habitat of slow-moving streams and shaded waterways in Papua New Guinea and northern Australia.
Creating a Suitable Environment
A nano tank with plenty of fine-leaved plants, moss, and floating vegetation is perfect for these fish. Plants provide hiding spots, reduce stress, and encourage natural foraging behaviour. Open swimming areas are also essential, allowing the school to move freely and display their colours to full effect. Substrate can be fine sand or small gravel, and adding driftwood or leaf litter helps replicate their natural environment.
Feeding and Nutrition
These fish are omnivorous and thrive on a varied diet. High-quality micro pellets or flakes form the base of their nutrition, supplemented with live or frozen foods like daphnia, brine shrimp, or microworms. Feeding small amounts multiple times a day ensures they stay healthy without compromising water quality.
Breeding Tips
Pseudomugil gertrudae are egg scatterers, and breeding them is relatively straightforward in a well-planted tank. Eggs are often laid among fine plants or moss, and gentle filtration increases fry survival. The fry are tiny and need infusoria or other micro-food initially before graduating to standard nano fish foods. With the right conditions, they grow quickly and begin to display their stunning colours within a few weeks.
Why They’re Underrated
Many hobbyists overlook these nano gems in favour of more commonly seen species, but their peaceful temperament, schooling behaviour, and brilliant colouration make them incredibly rewarding to keep. They’re perfect for planted nano tanks, community setups with other small species, or even as a standalone showcase species.
Final Thoughts
Pseudomugil gertrudae prove that size isn’t everything. Tiny but dazzling, they add movement, colour, and personality to any aquarium. With a little care, the right environment, and consistent feeding, these stunning nano fish can thrive and provide endless enjoyment for both beginner and experienced aquarists alike.