Gastromyzon sp. “Bloody Mary” (Hillstream Loach)

A striking and uncommon hillstream loach from Borneo, Gastromyzon sp. “Bloody Mary” is prized for its intense blood-red markings and rugged beauty. This micro-loach is a captivating choice for aquarists seeking both visual appeal and functional tankmates.

🧭 Overview & Origins

Belongs to the Gastromyzon fasciatus group, with bold red patches at the base of its dorsal fin and caudal peduncle

Wild-caught from Pangkalan Bun, southern Borneo—collected alongside the rare Gastromyzon sp. “Blue”

Unscientifically described; morphologically distinct from both G. fasciatus and G. praestans

🔍 Appearance & Behavior

Size: Reaches 5–6 cm (approx. 2–2.5 inches) as adults, though many imports arrive at 2.5–3.8 cm

Deep dark body with brilliant red markings that glow under strong oxygen flow

Courting males become almost black; females slightly smaller and more streamlined. Both sexes sport dermal tubercles (horny snout pimples)

🌿 Tank & Water Conditions

Tank size: Minimum 80 litres (~20 gallons). More space preferred for groups

Temperature: 20–24 °C

pH: 6.5–7.5, hardness 4–12 dGH, mimicking cool, oxygen-rich streams

Flow & Oxygen: High-oxygen, moderate-to-strong current is essential, provided via powerheads or strong filters

Substrate & Decor:

Use smooth stones, driftwood, caves and flat rocks for algae grazing stations.

Dense planting with riverine style structures adds both beauty and security.

🍽 Diet

Primary diet: Natural biofilm and algae growing on hard surfaces.

Supplemental foods: Algae wafers or spirulina tabs, blanched veggies (zucchini/spinach), and occasional live/frozen foods like daphnia or bloodworms

🧑‍🤝‍🧑 Social Behavior & Tankmates

Temperament: Calm, peaceful, best kept in groups of 3 or more to stimulate activity and reduce stress

Compatible species:

Small peaceful schooling fish (rasboras, danios, tetras)

Other hillstream loaches or bottom-dwellers (Otocinclus)

Shrimp and small snailsAvoid: aggressive, large, or fin-nipping species that may outcompete or harass them.

🧩 Breeding & Health Notes

Breeding: Rare or unconfirmed in home tanks; only glimpsed mating behaviors in tank studies and likely requires precise flow, tannin and substrate conditions

Found resilient in the wild—even surviving infections like Piscinoodinium without losses

✅ Summary: Why Keep Gastromyzon sp. “Bloody Mary”?

Stunning red–black contrast coloration makes this fish stand out

Hardy algae-eater suited for fast-current aquascapes

Peaceful and community-friendly when kept in groups

Rare, exotic, and visually compelling as a focal addition to river biotope tanks

🧾 Care Checklist (Metric Units)

Would you like help crafting a river-style aquascape or suggestions for ideal tankmates to pair with “Bloody Mary” loaches? 😊