Reticulated Hillstream Loach (Sewellia lineolata)

Common Name

Reticulated Hillstream Loach

Scientific name

Sewellia lineolata

Origin and Habitat

Endemic to central Vietnam, this species lives in clear, fast-moving mountain streams that flow over smooth stones and bedrock. The water is cool, highly oxygenated, and constantly moving. Substrates are made of rounded cobbles and pebbles covered in algae and biofilm, with sand and gravel in slower pockets. Seasonal rains increase flow and keep the habitat pristine. Sewellia lineolata has a flattened body and wide fins that allow it to cling securely to rocks in strong current, perfectly adapted for life in moving water.

Temperature and Water Conditions

Ideal temperature is 20 to 24 Celsius or 68 to 75 Fahrenheit. In the wild, the water is soft to moderately hard with a natural pH around 7.0 to 7.5. We do not recommend adjusting or chasing water parameters except in special cases such as breeding. The key to success is stable water, strong oxygen levels, and consistent flow. Clean, well-filtered water and good aeration are essential for long-term health.

Appearance and Size

A golden tan base is marked with intricate dark lines forming a reticulated pattern unique to each fish. The body is flattened with wide fins that create suction for gripping smooth surfaces. Adults reach about 6 centimeters, roughly 2.4 inches. Males have broader heads and may develop small tubercles on the front edge of their pectoral fins, while females are more rounded through the body when mature.

Diet in the Wild

In nature, this species grazes continuously on aufwuchs, a thin layer of algae, diatoms, and microorganisms coating submerged rocks. It also consumes tiny crustaceans, insect larvae, and other micro life living within this film.

Feeding in Captivity

Encourage natural grazing by providing algae-covered stones and driftwood. Offer high-quality sinking spirulina wafers, gel-based herbivore foods, and soft plant-based pellets. Supplement their diet with small live or frozen foods such as daphnia, cyclops, or finely chopped bloodworms several times per week. Feed small amounts and maintain good water movement to keep the food from collecting and spoiling.

Behavior and Tank Setup

Peaceful and very active in flow, Sewellia lineolata is not a schooling fish but does well in groups. A river-style aquarium suits them best. Create a long tank with strong directional flow using powerheads or a river manifold. Provide smooth stones, cobbles, and ledges for grazing and hiding. Bright light encourages algae growth and provides natural feeding surfaces. Keep a tight lid, as these loaches can climb glass. Ideal tank mates include white clouds, danios, rasboras, and other cool-water species that enjoy current and high oxygen levels.

Breeding

Breeding can occur in mature aquariums with strong flow and pristine water. Courtship usually takes place on or under stones. Eggs are deposited in narrow gaps or beneath rocks, often out of sight. Adults sometimes eat the eggs or fry, so separation increases survival rates. Rock piles and layers of larger gravel allow eggs to fall safely through, protecting them from adults and giving fry secure hiding spaces once they hatch. Fry graze on biofilm and can be fed powdered algae foods and infusoria at first, later progressing to micro worms and finely crushed prepared foods. Cool, stable water, high oxygen, and mature algae growth often trigger spawning.

Quick Facts

• Scientific name: Sewellia lineolata
• Common names: Reticulated Hillstream Loach, Vietnamese Hillstream Loach
• Origin: Central Vietnam mountain streams
• Size: About 6 centimeters, about 2.4 inches
• Temperature: 20 to 24 Celsius, 68 to 75 Fahrenheit
• pH: Naturally around 7.0 to 7.5; keep water stable rather than adjusting it
• Temperament: Peaceful grazer for cool, high-flow aquariums
• Diet: Aufwuchs grazer; accepts algae wafers, plant-based foods, and small live foods
• Breeding type: Stone crevice spawner
• Special care: Needs high oxygen and steady current

Tropical Fish Co. Notes

Sewellia lineolata is one of our favorite species for recreating a living stream environment. When given strong flow and algae-covered stones, these loaches glide gracefully like tiny stingrays and spend their days grazing. They are not typical algae cleaners but specialized fish that thrive in clean, oxygen-rich systems. We recommend keeping them in a dedicated hillstream setup or a cool-water community tank where they can show natural behavior. Focus on flow, oxygen, and stability rather than chasing parameters. Build a tank that mimics a mountain stream and you’ll see why this species has become a favorite among serious aquarists.