Yellowfin Hillstream Loach

The Yellow Finned Hillstream Loach, scientifically known as Gastromyzon viriosus, is a specialized river loach from the fast-flowing, rocky streams of Borneo (Tatau River basin, Sarawak). It clings to stones in high-oxygen water with its broadened pectoral and pelvic fins and spends most of the day grazing biofilm on hard surfaces.

Adult Yellow Finned Hillstream Loaches typically reach about 2 to 2.1 inches (5 to 5.4 cm). The body is flattened and disc-like, dark brown with 8–10 pale cream bars; mature fish develop distinctly yellow fins. The head shows a fine, pale reticulate pattern, and the eyes sit high for scanning while attached to rock.

A tank of at least 20 gallons with a long footprint is ideal for a small group. Provide a soft sand or fine gravel base covered with rounded river stones, cobbles, and slate to create extensive grazing area. Strong, laminar flow and very high oxygen are essential—use powerheads or a river-manifold setup—and keep lighting moderate to encourage natural algal films. A tight lid is recommended.

Water parameters should include a temperature of 68 to 75°F (20 to 24°C), a pH between 6.5 and 7.5, and soft to moderately hard water. Stability, pristine cleanliness, and vigorous aeration are critical to long-term success.

Feeding the Yellow Finned Hillstream Loach centers on biofilm and algae. Ensure a mature tank with algae-coated stones, and supplement with spirulina/algae wafers, gel foods, and blanched vegetables (zucchini, spinach). Offer small frozen items (daphnia, cyclops) sparingly; heavy protein diets can cause problems in hillstream grazers.

Yellow Finned Hillstream Loaches are peaceful but not true schoolers. Keep them in groups of three to six for natural interactions while providing multiple flow lanes and hides to diffuse minor squabbles. Suitable tankmates are other cool-water, current-loving species such as danios, white clouds, small rasboras, and freshwater gobies; avoid large or sluggish fish.

Breeding in home aquaria is rare and not well documented for this species. Spawning likely occurs on hard surfaces among stones, with no parental care; if fry appear, they require access to fine biofilm and microfoods.

Gastromyzon viriosus (Yellow Finned Hillstream Loach) is a compact, striking river specialist that rewards dedicated flow-tank keepers with constant foraging behavior, crisp barring, and vivid yellow fins in adulthood.