Hillstream loach

Quick facts

Adult size

6 cm

Lifespan

can live up to 8 years

Tank zone

bottom

Temperament

peaceful

Difficulty

intermediate

Schooling

recommended 3+ (critical minimum 2, thrives at 5+)

Typically wild-caught

yes - acclimate slowly

Water parameters

Temperature

18–24°C

pH

6.5 to 7.5

Hardness

5 to 15 dGH

Tank requirements

Minimum volume

75 L

Minimum length

75 cm

Flow

high

Lighting

bright

Substrate

any

Hiding spots

needed

Feeding

Diet: omnivore, feeds primarily at the bottom.

Biofilm grazers that rasp algae and microorganisms from hard surfaces. In a tank with established biofilm on rocks (which requires strong lighting and good flow), they graze continuously. Supplemental feeding with algae wafers, blanched zucchini, and spirulina-based sinking food fills any gaps. They don't eat standard fish food readily; sinking wafers left on a rock surface overnight are the best approach. Frozen bloodworm and brine shrimp are accepted occasionally but the diet should be heavily plant-based. Feed supplemental food every 1-2 days. A mature tank with good algae growth on rocks reduces the need for supplemental feeding.

Vegetable matter required (algae wafers, blanched zucchini, spinach).

Compatibility

• Specialized fish that needs high flow and cool, well-oxygenated water. This makes tankmate selection about the environment rather than temperament: only species that thrive in strong current and cooler temperatures (20–24°C) are suitable.
• Good companions: white cloud mountain minnows, danios, other hillstream species, and robust shrimp. Avoid tropical species that need still, warm water (gouramis, bettas, most cichlids).
• Males can be territorial toward each other over rock surfaces. In small tanks, one male per flat rock outcrop. In larger tanks (100 L) with multiple rock piles, several males coexist.
• The flat body is adapted for clinging to rocks in fast current. Watching them suction onto the glass and rock faces is part of the appeal. They look like miniature stingrays.

Habitat

A catch-all common name applied to several genera of loaches from fast-flowing mountain streams in Asia: Sewellia, Beaufortia, Gastromyzon, Pseudogastromyzon, and others. The species most commonly sold is Sewellia lineolata (reticulated hillstream loach) from central Vietnam, but several others appear in the trade under the same common name. All share the same body plan: dorsoventrally flattened body with broad pectoral and pelvic fins fused into a suction disc that allows them to cling to rocks in torrential current. Wild habitat is clear, cool (18–24°C), highly oxygenated streams and rivers flowing over boulders and cobble. The flow rates they inhabit would sweep most aquarium fish downstream. In the tank, replicating this means strong powerheads or river-manifold setups with smooth rocks and high dissolved oxygen. The species are subtropical, not tropical; warm water (above 25°C) stresses them and shortens their lifespan. Adult size varies by species: Sewellia reaches about 6–7 cm. The patterning is intricate, with dark reticulated lines on a lighter background, and varies between species and populations.

Breeding

Bred in home aquariums by experienced keepers, though not commonly. Strong current, cool water (20–22°C), and a mature tank with established biofilm on rocks appear to be the key triggers. Males are typically more colorful and may have more pronounced head spines. The female deposits a small number of eggs (10-30) on the underside of a rock in an area of strong flow. The male may guard the eggs. Eggs hatch in 10-14 days. Fry are tiny and cling to surfaces immediately, feeding on biofilm. In a tank with abundant biofilm, fry can survive without intervention. Dedicated breeders raise fry in separate containers with small pieces of biofilm-covered rock transferred from the main tank. Growth is slow. Breeding reports are species-specific and protocols differ between Sewellia, Beaufortia, and Gastromyzon.

Common problems

Inadequate flow is the number one setup error. Hillstream loaches in a standard low-flow community tank decline over months. They need a river-tank setup with powerheads creating visible current across rock surfaces. Temperature above 25°C causes chronic stress. Starvation from insufficient biofilm in new or sterile tanks is the other major killer. The tank needs to be mature (3+ months running with strong light on the rocks to grow biofilm) before adding hillstream loaches. Supplemental feeding with algae wafers helps bridge the gap. Sensitivity to medications, especially copper-based treatments, means half-dose protocols for any chemical treatment. The species mix sold under the 'hillstream loach' label means care guides are often too generic; look up the specific genus you have.

Bioload

Bioload coefficient: 1.4 (small biofilm-grazing loach; modest waste output).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size