Hillstream loach

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Typically wild-caught; acclimate slowly.

Feeding

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.

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.

Origin and habitat

Native to Vietnam: provinces of Thua Thien-Hue (Huong River), Quang Nam (Thu Bon River), Quang Ngai (Tra Khuc and Ve Rivers), and Binh Dinh (An Lao River). Also recorded from Khone Falls on the Mekong in Laos near the Cambodia border. IUCN Vulnerable. Family Gastromyzontidae. Also called the tiger hillstream loach, reticulated hillstream loach, or gold ring butterfly sucker. Size about 6.4 cm. The body is flattened with broad pectoral and pelvic fins forming a ventral suction disc for clinging to rocks in strong current. Scales are present but tiny. Males develop rows of soft raised tubercles ("fences" in hobbyist terminology) on the first 5-6 pectoral fin rays, plus additional rows on the head; females have a broader head and stouter body. They feed mainly on micro to macro aquatic invertebrates inhabiting the periphyton on submerged rocks. They need established biofilm and algae on surfaces. They are strictly diurnal. The critical habitat requirement is high flow and oxygenation to replicate their steep-gradient hill stream habitat. Lifespan 5-10 years in proper conditions. Easily bred in aquaria among Sewellia species.

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

Further reading

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