Hillstream Loach
Sewellia lineolata
Min Tank Size
75L
Adult Size
7.5 cm
Lifespan
8 years
School Size
5+
About
Native to fast-flowing, highly oxygenated hill streams in Vietnam and Laos, Sewellia lineolata is built like nothing else in the hobby. Its body is flattened dorso-ventrally, with a broad pectoral and pelvic fin arrangement that functions almost like a suction disc, letting it cling to smooth rocks in fierce current. The reticulated pattern of cream lines and spots on a brown base makes them genuinely beautiful up close, and watching one zip across glass or anchor in a powerhead blast is endlessly entertaining. Males develop fleshy tubercles on their snouts and have a slightly broader head, which helps with sexing once you know what to look for.
Water parameters matter more here than with most community fish. Temperature should stay between 20 and 24 degrees Celsius. They're mountain stream animals and will become lethargic and disease-prone if kept warm. 5 suits them well, and moderate hardness is fine. The nonnegotiable is flow and oxygen. These fish suffocate in still or even gently moving water. A powerhead or wavemaker pointed across smooth rocks is the baseline setup, not a bonus.
Diet is almost entirely biofilm, periphyton, and algae scraped from hard surfaces. They will graze on algae wafers and blanched vegetables but truly thrive when the tank has a mature film coating rocks and glass. Getting them to feed reliably in a new tank is one of the biggest early challenges.
Peaceful with nearly everything, but males don't always tolerate each other. Browse tank builds featuring this species to see how hobbyists nail the high-flow hardscape.
Water Parameters
Temperature
°CpH
GH
dGHKH
dKHSwimming Level
Flow Preference
Keeping multiple Hillstream Loach together
Hillstream Loach are shoaling fish and need company of their own kind. Keep a group of at least 5. Smaller groups leave them stressed, washed-out in color, and prone to hiding.
Compatibility
Sewellia lineolata works well with fast-water species that share their environmental needs. White Cloud Mountain Minnows, Danios, and smaller Devario species make natural companions since they all come from similar biotopes and tolerate the same cool, highly oxygenated water. Avoid slow-water tropical fish like discus, angelfish, or betta, partly for temperature reasons and partly because those fish can't handle the flow these loaches require. Nano shrimp like Neocaridina coexist peacefully, though shrimp should be well fed so they aren't competing for biofilm. Keep only one male in smaller tanks. A 120-liter or larger tank opens up options for a trio.
Commonly kept with
Species this one is most often paired withCommonly tried but avoid
Often paired, but shouldn't beCare Notes
The two most common failure points are temperature creep and biofilm starvation. Beginners often keep them in tanks running 26 to 28 degrees because that suits the rest of their community, and the loaches slowly decline. A dedicated cool-water setup or a species tank is usually the right call. The other killer is adding them to tanks under six months old where biofilm hasn't developed. They'll graze algae wafers but don't thrive on them alone. Seed the tank early, let rocks and glass mature, and supplement with spirulina-based foods while the biofilm builds up.
Behavior & Aggression
Conspecific tension is the main concern, specifically between males. They use lateral displays, chasing, and physical skirmishes to sort out territory over choice feeding spots on rocks and glass. In larger tanks with plenty of broken line-of-sight from rocks, a small group can coexist reasonably well. In cramped or sparse setups, the dominant male will relentlessly harass subordinates. Mixed sex groups of three or more tend to distribute the tension better than a simple pair. They show no aggression toward unrelated species.
Things to Know
- Needs strong water flow and very high oxygen, powerheads essential
- Males will chase and fight each other, especially in smaller tanks
- Requires established biofilm, new tanks often starve them out
- Sensitive to high temperatures, keep below 24C strictly
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