Pacific Blue Eye
Pseudomugil signifer
A sparkling Australian native nano fish with brilliant blue eyes.
| Difficulty | Beginner |
| Min. Tank Size | 40 L |
| Temperature | 18.0–28.0 °C |
| pH Range | 6.5–8.0 |
| Max Size | 3.5 cm |
| Lifespan | 2-3 years |
| Diet | Omnivore |
| Temperament | Peaceful |
Overview
The Pacific Blue Eye (Pseudomugil signifer) is a sparkling Australian native nano fish with brilliant blue eyes. It is a popular choice among Australian aquarists, reaching around 3.5 cm and living roughly 2-3 years when properly cared for.
This complete guide covers how to keep the Pacific Blue Eye successfully - tank size and setup, water parameters, the best foods (including recommended brands), suitable tank mates, breeding, sexing and the health issues to watch for. It is rated Beginner to care for.
Natural Habitat & Origin
This is an Australian native species, adapted to local rivers and billabongs. Many natives tolerate cooler water and are hardy, but they often grow large and are powerful swimmers that need space.
Matching the temperature, water chemistry and cover a species evolved with is the simplest route to keeping it healthy and seeing its natural behaviour and colour.
Tank Size & Aquarium Setup
Provide a minimum of 40 litres for the Pacific Blue Eye. As a group-living species, swimming length and floor space matter more than height.
A tight-fitting lid is essential - this species is a capable jumper.
Live plants, driftwood and shaded retreats give security and show off the fish's colours against a natural backdrop.
Always add fish only to a fully cycled, mature tank with stable biological filtration. Provide strong, well-oxygenated flow for this active, oxygen-hungry species.
Water Parameters
Keep the Pacific Blue Eye in stable water at 18-28 °C with a pH of 6.5-8.0. It adapts to a moderate range, so stability matters more than an exact figure.
Test regularly: ammonia and nitrite must read zero, and nitrate should be kept low with routine partial water changes. Always dechlorinate and temperature-match new water, because sudden swings cause far more illness than water that is stable but slightly imperfect.
Diet & Feeding
The Pacific Blue Eye is an easy-going omnivore that accepts a wide range of foods.
In Australia, good options include API Tropical Flakes or Pellets, Hikari Micro Pellets or Tropical, and Dymax frozen brine shrimp and bloodworm as treats. Feed small amounts once or twice a day (only what is cleared in a minute or two), vary the diet for the best colour and health, and avoid overfeeding, which is the leading cause of poor water quality.
Temperament & Tank Mates
The Pacific Blue Eye is peaceful and community-friendly. It mixes well with other calm species that share its temperature (18-28 °C) and pH (6.5-8.0) needs, are too large to be eaten and not large enough to eat it.
Crucially, keep the Pacific Blue Eye in a group of at least 6 (8 or more is better). A proper shoal is calmer, bolder, more colourful and far less likely to harass tank mates - keeping too few is a common cause of stress and nipping.
Breeding
The Pacific Blue Eye is an egg-scattering species. To breed it, condition a group on rich foods, then move them to a dim tank with fine-leaved plants or a spawning mop; the parents scatter eggs and will eat them, so remove the adults after spawning.
Even if you are not planning to breed it, recognising this behaviour helps you understand what you are seeing and respond well - for example by adding cover for fry or giving a guarding pair extra space.
How to Tell Males from Females
Sexing varies by species; males are often more colourful in breeding season while females are rounder when carrying eggs.
Common Health Problems
Like most aquarium species it can suffer from white spot (ich), fin rot and fungal or bacterial infections, almost always triggered by stress or poor water quality. Quarantine new arrivals for 2-4 weeks and watch daily for early signs such as loss of appetite, unusual hiding, clamped fins or laboured breathing - caught early, most issues are very treatable.
Prevention beats cure: keep water pristine, avoid overstocking and overfeeding, quarantine new arrivals, and act at the first sign of trouble.
Is the Pacific Blue Eye Right for You?
The Pacific Blue Eye suits beginners and experienced keepers alike, as long as you can provide at least 40 litres, water at 18-28 °C and pH 6.5-8.0, the right diet and a proper group of its own kind.
Meet those needs and the Pacific Blue Eye will reward you for around 2-3 years. Use our free aquarium calculators to plan your setup, and explore our other fish, plant and disease guides to build a thriving aquarium.
How to Tell Males from Females
Males are deeper-bodied, more strongly coloured and develop a more pronounced arch to the back with age. Females stay slimmer and paler. Colour alone is unreliable in young fish, since males only develop fully from around a year old.
