Hillstream Loach

Sewellia lineolata

Also known as: Reticulated hillstream loach, Tiger hillstream loach, Butterfly loach

Water Parameters

• Temperature: 18–24°C
• pH: 6.5–7.5
• Hardness (GH): 71–214 ppm (4–12 dGH)

Values above are general hardness (GH). For carbonate hardness (KH), the buffer that keeps pH stable, see the water parameters guide.

Care Summary

An aquatic oddity that looks more like a tiny stingray or a living lichen than a loach: a flat, broad-finned, beautifully reticulated fish that clings to rocks and glass in fast current with a sucker-like underside, grazing biofilm. Hillstream loaches are charming and increasingly popular, but they are habitat specialists, not general community fish, and most losses come from ignoring that. They need cool, clean, turbulent, oxygen-rich water (a powerhead or strong filter return), a mature tank with rock surfaces coated in the algae and biofilm they eat, and tankmates that suit the same cool, brisk conditions. Given a purpose-built hillstream or temperate setup they are hardy and fascinating, spending the day grazing and the breeding season in gentle territorial display. A rewarding fish for a keeper willing to build the tank around it, rather than fit it into an existing tropical community.

Tankmates

A specialist that thrives only in conditions most community tanks do not provide: cool, fast-flowing, highly-oxygenated water over rocks coated in the biofilm and soft algae it grazes. Its compatibility is driven by those needs rather than by temperament, as it is entirely peaceful (males squabble harmlessly over grazing spots). The right tankmates share its love of cool, brisk water: white cloud mountain minnows, danios, hillstream-friendly barbs like rosy and denison barbs, and other temperate species, plus shrimp, with which it is safe. It is a poor match for warm, still-water fish such as bettas, discus, and rams. Crucially it needs a mature tank with established algae and biofilm to feed on; it will slowly starve in a new or spotless tank despite supplementary feeding.

Compatible with

• White Cloud Mountain Minnow
• Zebra Danio
• Rosy Barb
• Denison Barb
• Bristlenose Pleco
• Cherry Shrimp

Avoid keeping with

• Betta
• Discus
• German Blue Ram
• Large Cichlids
• Tropical Warm Water Species

Common Problems

• starvation in tanks without established biofilm and algae
• stress and decline in warm, still, or low-oxygen water
• sensitivity to poor water quality
• being kept in unsuitable warm tropical communities

Sources: seriouslyfish.com, fishbase.org · Last updated: 2026-06-20