Pacific blue-eye

1) Where they come from

Pacific blue-eyes (Pseudomugil signifer) are little Aussie natives from coastal creeks, lagoons, and estuaries—places where the water can swing from fresh to slightly salty depending on tides and rain. That “in-between” lifestyle is why they handle brackish setups so naturally.

2) Setting up their tank

These are small fish, but they look and act better with space to cruise. A longer tank beats a tall one. I’ve kept them in 15–20 gallons with great results, and a 10 can work if you keep the group small and stay on top of maintenance.

• Tank size: 15–20 gal is a sweet spot for a proper group; 10 gal is doable for a smaller school
• Group size: aim for 8–12+ if you can—males show more color and they’re less jumpy
• Flow: gentle to moderate; they like to swim into it but don’t want a washing machine
• Filtration: sponge filter or a small HOB with a prefilter sponge (they love picking at biofilm)
• Temperature: mid 70s°F works well (around 24–26°C)
• pH/hardness: they’re not fussy if it’s stable, but they generally like it a bit on the hard/alkaline side

For brackish, go light. Think “a little coastal” rather than full marine. Mix marine salt (not aquarium/table salt) in a bucket, then add it to the tank so you’re not sprinkling salt onto fish and plants.

Decor-wise, they’re happiest with a mix of open swimming room and fine-leaved plants to weave through. In brackish, you can use hardy stuff like Java fern and Anubias (often okay in low salinity), plus brackish-friendly options like Vallisneria, some Crypts (variable), or even mangrove roots if you want the look. I always add spawning mops or a clump of guppy grass-type cover if it tolerates your salinity—gives them confidence and doubles as an egg spot.

3) What to feed them

They’re tiny-mouthed, fast little pickers. Mine always did best with small foods offered more than once a day. If you only feed big flakes once, you’ll think they’re “picky,” but really the pieces are just too chunky or sink too fast.

• Staples: finely crushed quality flakes or small micro-pellets (slow-sinking is perfect)
• Frozen: baby brine shrimp, cyclops, daphnia (great for color and breeding condition)
• Live (if you can): baby brine shrimp, microworms, vinegar eels—absolute cheat codes for getting them to spawn
• Feeding rhythm: small amounts 1–2x/day; they do better with “snacking” than big meals

4) Behavior and tankmates

Pacific blue-eyes are peaceful, busy, and honestly pretty entertaining. Males posture and “flash” at each other, but it’s more like sparring than real fighting. In a good-sized group, the bossy behavior spreads out and everyone stays calmer.

• Temperament: peaceful, active schooling fish
• Best look: more females than males, or at least don’t pack a tiny tank with all males
• Tankmates (brackish-leaning): other small, calm fish that won’t outcompete them at feeding time
• Avoid: fin-nippers, big boisterous fish, and anything that thinks a 1.5-inch fish is a snack

They can be a little shy the first week, especially in a bare tank. Add plant cover, keep the lights not-too-blinding, and give them time. Once they settle, they’re out all day.

5) Breeding tips

If you give them good food and somewhere to put eggs, they’ll usually do the rest. They’re egg scatterers that like fine-leaved plants or spawning mops. I’ve had the most luck collecting eggs from a yarn mop every couple of days and hatching them separately—otherwise the adults (and even the other fry) will snack.

• Spawn trigger: heavier feeding (especially live/frozen) + regular water changes
• Where eggs go: spawning mop, Java moss-style clumps, fine plants
• Egg handling: move the mop/eggs to a small container with gentle aeration
• Hatch time: usually about 1–2 weeks depending on temperature
• First foods: infusoria-style foods, rotifers, or vinegar eels; then baby brine shrimp once they can take it

6) Common problems to watch for

Most issues I’ve seen with these come down to three things: unstable water, not enough group size, and diet that’s too coarse. They’re tough for a “delicate-looking” fish, but they don’t love sudden swings.

• Jumping: open tops and gaps around tubing are the #1 killer—cover everything
• Wasting/skinny fish: food pieces too big, or tankmates outcompeting them at meals
• Clamped fins/shyness: group too small, tank too bare, or too much aggression from tankmates
• Salt mistakes: using the wrong salt (use marine salt mix) or changing salinity too fast
• New-fish issues: they can arrive stressed—go easy on lighting, feed small foods, and keep water clean