Quick Stats
| Adult Size | 5–7 cm |
| Minimum Tank | 20 gal |
| Temperature | 20–24°C |
| pH Range | 6.5–7.5 |
| Hardness (GH) | 5–12 dGH |
| Difficulty | Medium |
| Temperament | Peaceful |
| Diet | Herbivore/Grazer — algae, biofilm, algae wafers, blanched vegetables |
| Schooling | 1 alone or 3+ in a group |
Tank Setup
Hillstream loaches (Sewellia lineolata and related species) are adapted to fast-flowing, cool, highly-oxygenated mountain streams in Vietnam and China. They are not a general community fish. A 20 gallon long tank with a powerhead is the realistic minimum; a standard tropical community tank will slowly kill them through oxygen starvation.
Water parameters: temperature 20–24°C (NOT tropical — 26°C is too warm long-term), pH 6.5–7.5, hardness 5–12 dGH. The non-negotiables are flow and oxygen: they need a powerhead creating visible surface agitation, or they will gasp and decline.
Set up the tank with smooth river stones, slate stacked to create crevices, and a bare or fine-sand substrate. Plants are optional — Anubias and Java fern attached to hardscape survive the current; stem plants will not. The key is to create surfaces they can cling to: smooth rocks with a thin film of algae are what they actually want.
Tank Mates
Hillstream loaches are peaceful and completely ignore other fish. The challenge is finding species that share their cool, fast-flow requirements.
Compatible tank mates: White Cloud Mountain Minnows (perfect temperature overlap), Zebra Danios (at the cool end), Rhinogobius gobies, and other hillstream-adapted species. Cherry Shrimp and Amano Shrimp also thrive in the same conditions.
Avoid tropical species that need 26°C+ — the hillstream loach will slowly suffocate at that temperature even with strong flow. Also avoid aggressive bottom-dwellers (cichlids, large catfish) that will outcompete them for food.
Diet & Feeding
Hillstream loaches are primarily herbivorous grazers. In a mature tank they will spend all day rasping algae and biofilm off smooth surfaces. In a new tank with little algae, supplement heavily with algae wafers, blanched zucchini, cucumber, and spinach.
Feed once daily in the evening — they are most active at night. Drop an algae wafer near their favourite resting rock; they will find it within minutes. Avoid heavy protein diets (bloodworms, brine shrimp) — they cause digestive issues in this species.
A healthy hillstream loach should have a slightly rounded belly. If yours looks hollow, the tank doesn't have enough algae and you need to feed more vegetables. They are slow eaters and will lose out to faster fish at feeding time.
Common Health Issues
The single biggest killer of hillstream loaches is warm, low-oxygen water. If the tank is above 24°C, they will gasp, refuse food, and decline over weeks. The fix is always the same: lower the temperature and add a powerhead.
They are also prone to starvation in community tanks — faster fish eat all the food before the loach finds it. Watch for hollow bellies and feed algae wafers after lights-out when other fish are inactive.
Sensitive to copper and many medications — always research compatibility before treatment. Standard quarantine is 2 weeks. Lifespan is typically 5–8 years in a properly set up hillstream tank.
Breeding
Breeding hillstream loaches in the home aquarium is uncommon but documented. They spawn on smooth rocks in fast-flowing water, scattering adhesive eggs that hatch in 48–72 hours.
Triggers appear to be: a temperature drop of 3–4°C (simulating spring), a major increase in flow, and a sudden abundance of algae/biofilm. Conditioning with extra vegetable feedings for 2–3 weeks before helps.
Fry are tiny and need infusoria for the first week, then graduate to powdered algae wafers and microworms. Most successful breeding happens in dedicated hillstream-species tanks rather than community setups.
Frequently Asked Questions
What size tank does a Hillstream Loach need?
A 20 gallon long tank is the minimum — they need horizontal swimming space, not depth. The tank must have a powerhead creating genuine current; a standard filter is not enough.
Do Hillstream Loaches need a heater?
No — they prefer cool water at 20–24°C. An unheated tank in a temperate-climate house is ideal. Sustained temperatures above 26°C cause oxygen stress and shorten their lifespan.
Are Hillstream Loaches good algae eaters?
Yes — they are exceptional algae grazers, especially on flat smooth surfaces like glass and slate. However, they only thrive in cool, high-flow tanks. If you have a standard tropical community tank, choose Nerite snails or Otocinclus instead.
Can Hillstream Loaches live with tropical fish?
Only with species that tolerate the cool end of tropical (22–24°C). Most tetras, guppies, and bettas need 26°C+, which is too hot for hillstream loaches long-term. They do best in a dedicated cool-water hillstream setup with White Clouds or Danios.