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

Sewellia lineolata is a flattened, rock-clinging loach from the fast, clear mountain streams of central Vietnam, with records extending into Laos and Cambodia. It belongs to the hillstream loach family and reached the aquarium trade in the mid-2000s, where it became one of the more popular species under names like reticulated, tiger, or Vietnamese hillstream loach and gold ring butterfly sucker. The common label hillstream loach is used loosely across several genera, so care advice written for one does not always fit another. The body is built for life in current: broad pectoral and pelvic fins spread into a ventral suction disc that lets the fish hold station on smooth rock in heavy flow. Scales are reduced and the body is sensitive to medication, so it is generally treated like a scaleless fish. Males are slimmer and carry rows of small raised tubercles on the leading pectoral rays and head, while females are broader and stouter. In the wild it grazes the periphyton, the biofilm and tiny invertebrates coating submerged rocks, and it feeds during the day. It reaches around 6 cm.

Breeding

Among the easier hillstream loaches to spawn, and bred fairly regularly by keepers with a suitable setup. The triggers seem to be strong flow, cool water in the low twenties Celsius, and a mature tank with plenty of biofilm. The male clasps alongside the female and eggs are laid in flowing areas over rock; a layer of larger gravel lets the eggs drop out of reach of hungry adults. The fry cling to surfaces and graze biofilm from the start, so an established, algae-rich tank lets some survive without help, while dedicated breeders move biofilm-covered rock or rear fry separately on powdered algae foods. Growth is slow, and detailed methods differ between Sewellia and the other hillstream genera.

Common problems

Too little flow is the usual reason these loaches fail; in a standard calm community tank they slowly decline, so they need a river-style setup with powerheads driving visible current across the rocks and high oxygen at the surface. Heat is the other problem, since they want cool water and suffer if it stays much above the mid-twenties. Starvation is a real risk in a new or sterile tank, because they depend on grazed biofilm; the tank should be mature with good algae growth before they go in, with algae wafers to fill any gap. Their thin skin makes them sensitive to medications, so chemical treatments, especially copper, should be used cautiously at reduced doses.

Bioload

Further reading

• Biotope aquariums: matching fish to their natural habitat
• Keeping shrimp with fish: what actually works
• How water temperature affects fish metabolism