Kasi Blue Eye Pseudomugil Cyanodorsalis Care Guide: Indonesian Wild

Few nano fish carry the electric blue dorsal flash of Pseudomugil cyanodorsalis, the Kasi blue eye from Sulawesi and Papua. The kasi blue eye pseudomugil stays under 4cm yet brings movement, schooling chemistry and a wash of cobalt that dominates a planted tank far larger than its body suggests. This guide from Gensou Aquascaping at 5 Everton Park covers what makes the species different from its more common cousins, why a group of eight is the floor not the ceiling, and how Singapore tap water needs softening before a wild import will settle.

Origin and Habitat

Kasi blue eyes were first collected from coastal streams in Sulawesi and the Papuan provinces, where they shoal across shallow tannin-stained pools with mild brackish influence near river mouths. The species name cyanodorsalis translates to “blue back,” referring to the iridescent stripe along the dorsal ridge that flashes only when males display. Wild populations face habitat pressure from palm-oil expansion, which has pushed prices on Indonesian exports up over the past five years.

Identifying a True Kasi Blue Eye

Confusion with the spotted blue eye (P. gertrudae) and the forktail (P. furcatus) is constant in Singapore shops because juveniles look almost identical. Kasi adults show a slim cylindrical body, a single bright blue dorsal flash that runs from nape to dorsal fin, and pale yellow finnage with black trailing edges in mature males. Females are dustier and slightly smaller at 3-3.5cm.

Schooling and Group Dynamics

Eight is the absolute minimum. In smaller groups they sulk, hide and never display. A pod of twelve to fifteen produces constant in-school flaring between males who use the dorsal flash as a territorial flag rather than fighting physically. Stocking ratios of two females per male prevent any single hen being harassed.

Tank Size and Aquascape

A 45-litre planted nano works for eight; sixty litres gives a fifteen-strong school proper swimming length. Long tanks with horizontal sightlines beat tall cubes because pseudomugils cruise the upper third in formation. Use fine sand, dense midground planting with Cryptocoryne wendtii, floating Salvinia for diffused light, and one or two pieces of slim driftwood from the decoration and substrate range.

Water Parameters

Despite mild brackish tolerance in the wild, captive Kasi blue eyes thrive in pure soft fresh water at pH 6.0-7.0, GH 2-5, KH 1-3, and 24-28°C. PUB tap water sits close to that profile straight out of the tap once chloramine is removed. A small QANVEE Bio Sponge Filter on low flow keeps oxygenation up without buffeting the tiny fish.

Acclimation for Wild Imports

Kasi blue eyes ship from Indonesia stressed and skinny. Drip acclimate over 60 minutes minimum, dim the lights for the first 48 hours, and feed live Artemia nauplii from day one — they often refuse dry food until they recover condition. Quarantine for three weeks separately before introduction, treating prophylactically for flukes with Praziquantel.

Diet

The mouth opens to roughly 1mm wide, so any food larger than crushed flake is wasted. Live or frozen baby brine shrimp, microworm, daphnia and cyclops drive the best colour. Supplement with finely crushed Hikari Micro Pellets twice daily. Carotenoid-rich food intensifies the yellow body wash and makes the blue dorsal pop by contrast.

Tank Mates

Pair with other tiny soft-water nano species — chili rasbora, ember tetra, Pygmy Cory, Sundadanio. Avoid anything aggressive, fast or large enough to outcompete at feeding. Shrimp tankmates work, though Kasi blue eyes do pick at newly hatched shrimplets, so dense moss cover protects the breeding colony.

Sourcing in Singapore

Iwarna and a handful of Carousell wild-fish specialists carry Kasi blue eyes seasonally at SGD 8-15 per fish, usually in batches of twenty after each Indonesian shipment lands. Buy the whole batch if you can — uniform fish from a single import settle far faster than mixed-source groups. Set up the tank with the aquarium tank range from Gensou two weeks before the order arrives so the biofilm is mature.

Related Reading

• Spotted Blue Eye Pseudomugil Singapore Care Guide
• Wild Caught Fish Acclimation Protocol Singapore Guide
• Wild Caught vs Tank Bred Decision Guide
• Native Singapore Freshwater Species Overview Guide
• Sumatran Rainforest Biotope Aquascape Design Guide