Red Devil Hillstream Loach

Common Name

Half Red Borneo Sucker. Also sold simply as a hillstream loach. The cf. marker means the fish closely resembles Gastromyzon russulus, yet may be a regional form that still needs taxonomic study.

Origin and Habitat

Native to Borneo hillstreams. Collected from clear, cool tributaries where water races over bedrock and rounded stones. Riffles and shallow runs provide steady current and very high oxygen. Substrates are slabs of rock, cobble, and coarse gravel with pockets of sand. Plants are sparse in the fastest lanes, while calmer margins hold leaf litter and occasional rheophytic ferns or mosses.

Temperature and Water Conditions

Aim for cool to mid tropical water with vigorous aeration and clean, strong flow. A practical range is 20 to 24°C, which is 68 to 75°F. Reports from similar habitats and long term aquaria place pH near neutral to slightly alkaline, about 6.5 to 7.8, with soft to moderate hardness. We do not recommend chasing or altering numbers except for special breeding situations. Stable conditions, very high dissolved oxygen, and low nitrogen waste matter far more than exact values.

Appearance and Size

A compact, flattened river loach built for current. The base color is chocolate to slate with pale spotting, and a warm red to orange wash often develops over the rear half of the body and tail when the fish is settled and well fed. Wide pectoral and pelvic fins act like suction pads on rock. Adults reach about 4 to 5 cm standard length, which is 1.6 to 2.0 inches. Sexes are similar, males may show a slightly broader head and sharper color when in peak condition.

Diet in the Wild

A specialist periphyton grazer. It scrapes biofilm from stone and wood, taking diatoms, filamentous green algae, small amounts of cyanobacteria, and the tiny invertebrates that live inside that film.

Feeding in Captivity

Success begins with seasoned rock. Allow smooth stones and slate to develop a green film under good light. Offer spirulina rich wafers, algae based micro pellets, and gel foods pressed onto flat stones. Add small portions of frozen cyclops, daphnia, and spirulina enriched baby brine shrimp as supplements, not as the main course. Place food directly on rock surfaces in the current so the fish can graze naturally.

Behavior and Tank Setup

Peaceful and best kept in a group so individuals can establish small rock centered stations without stress. Use a long aquarium with a river style manifold or added powerheads to create broad, even flow. Provide strong aeration, excellent mechanical and biological filtration, and frequent small water changes. Hardscape should be rounded cobble, slate plates, and boulders with patches of fine sand or smooth gravel to protect the belly. Plants are optional. Hardy rheophytes such as Anubias, Microsorum, and mosses tied to rock do well along calmer edges. Good companions include danios, white clouds, small rasboras, and gentle rheophilic gobies that enjoy the same cool, fast water.

Breeding

Home breeding is rarely documented for this form, yet behavior is presumed similar to other Gastromyzon. Courtship likely occurs on or between stones, with adhesive eggs placed in crevices and no parental care. If you wish to try a project, think like a mountain stream. Keep flow brisk, oxygen near saturation, and water immaculate. Build layered rock piles and include pockets of larger rounded gravel as a starting point, since these structures create natural gaps that shelter eggs from current and tank mates. Allow biofilm to flourish so newly hatched fry find immediate micrograzing. If eggs are found, move them gently to a small container with matching water and a fine bubble across the clutch. First foods are infusoria and quality fry powders, then newly hatched baby brine shrimp once fry are large enough.

Quick Facts

• Scientific name: Gastromyzon cf. russulus
• Origin: Borneo hillstreams with clear, fast water
• Size: About 4 to 5 cm standard length, which is 1.6 to 2.0 inches
• Temperature: 20 to 24°C, which is 68 to 75°F
• pH: Commonly 6.5 to 7.8 in reports, stability is more important than exact value
• Temperament: Peaceful grazer, forms small rock centered stations
• Diet: Periphyton grazer that consumes algae, diatoms, and micro invertebrates
• Breeding: Rarely documented in aquaria, presumed crevice spawner without parental care, rock piles and larger gravel help protect eggs and fry

Tropical Fish Co. Notes

When the stones are green and the flow hums, this fish turns a river tank into a living documentaries channel. The half red glow over the back half shows best against light sand and clean, moving water. Focus on oxygen first, then flow, then food. Give them seasoned rock, keep the water pristine, and they will reward you with constant, charming activity. If you explore breeding, those rock piles and larger gravel pockets are your first smart step. Record every detail so other hobbyists can build on your success.