Reticulated hillstream loach

1) Where they come from

Reticulated hillstream loaches (Sewellia lineolata) come from fast, cool-ish streams in Vietnam and nearby areas. Think shallow water ripping over smooth stones, tons of oxygen, and biofilm growing on every surface. If you build your tank around that vibe, they’re surprisingly hardy.

2) Setting up their tank

These guys aren’t “bottom fish” in the usual sense—they’re more like little suction-cup hovercrafts. They want flow, oxygen, and lots of hard surfaces to graze. A pretty tank that’s low-flow and plant-jungle usually disappoints them.

• Tank size: 20 gallons long is a great starting point (bigger is easier).
• Flow: aim for brisk current across the bottom; powerheads or a strong filter return help a lot.
• Oxygen: surface agitation matters; they act stressed in stagnant water.
• Substrate: sand or small smooth gravel—skip sharp stuff.
• Hardscape: smooth river stones, rounded cobbles, and some driftwood for biofilm.
• Plants: use tougher stuff that tolerates flow (Anubias, Java fern, Bolbitis).

Water-wise, they do best in clean, stable freshwater. I’ve had the best luck keeping them on the cooler side with strong circulation. They can handle a range, but they don’t love warm, sluggish tanks.

• Temperature: ~68–74°F (20–23°C) is a sweet spot in most homes.
• pH: usually fine anywhere around neutral (roughly 6.5–7.5).
• Hardness: moderate is totally workable—stability beats chasing numbers.
• Maintenance: frequent small water changes beat occasional big ones.

3) What to feed them

They look like algae-eaters (and they are), but they’re not a magic cleanup crew. In a bare or super-clean tank they’ll run out of natural grazing fast. In my tanks, the best results came from treating them like constant grazers plus a little “real food” every day.

• Staples: algae wafers, spirulina pellets, Repashy Soilent Green (or similar gel foods).
• Frozen: baby brine shrimp, daphnia, cyclops (great for variety).
• Fresh: blanched zucchini/cucumber (works better if you rough up the skin a bit).
• Natural: encourage biofilm—let some rocks sit under bright light in a spare container and rotate them in.

Watch their bellies. A well-fed Sewellia has a gently rounded belly and spends a lot of time calmly grazing. A pinched belly + frantic glass surfing is your cue to increase food availability and check flow/oxygen.

4) Behavior and tankmates

They’re peaceful, but they do have a little “king of the rock” attitude with each other. You’ll see chasing and posturing—like tiny stingrays having a disagreement. It’s usually harmless if the tank has enough surface area and multiple perches.

• Best group size: 3–6+ if you have room (they’re more fun in a group).
• Territory: give lots of flat stones so nobody has to fight over the one good spot.
• Good tankmates: danios, white clouds, small barbs, rasboras, and other current-loving peaceful fish.
• Also works: other hillstream species if the tank is big and food is plentiful.

They spend a lot of time on glass, stones, and broad leaves. If you never see them out, something’s off—usually not enough oxygen/flow, too much harassment, or not enough grazing spots.

5) Breeding tips

They can breed in captivity, and it’s one of the cooler “surprise spawns” in the hobby. Most people who pull it off weren’t running a dedicated breeding tank—they just had a mature, high-flow setup with lots of crevices and they fed well.

• Start with a group so you likely have both sexes (sexing is subtle until they’re mature).
• Mature tank: lots of biofilm, stable parameters, and plenty of hiding cracks between stones.
• Conditioning: heavier feeding with frozen foods + quality algae-based foods.
• Spawning sites: rock piles with gaps, rounded pebbles, and sometimes filter intake areas.

6) Common problems to watch for

Most Sewellia issues come down to the “river fish in a lake tank” mismatch: not enough oxygen, not enough flow, or not enough grazing. Fix the environment and they usually bounce back fast.

• Slow starvation: they eat, but still get thin because there’s not enough constant grazing. Add biofilm surfaces and feed more frequently.
• Outcompeted at meals: common in busy community tanks. Try target feeding or night feeding.
• Low oxygen/low flow stress: glass surfing, hanging near the surface, lethargy. Increase surface agitation and current.
• New tank syndrome: they do poorly in unstable tanks—ammonia/nitrite spikes hit them hard.
• Ich/parasites after purchase: they can come in rough from shipping; quarantine helps a lot.
• Medication sensitivity: like many loaches, they can react badly to strong doses (especially copper). Go slow and research the med first.

Once you nail the flow + oxygen + food availability, they’re one of those fish that make you stop and watch the tank. Mine spend the day grazing in little patrol routes, and the occasional rock-top wrestling match is basically free entertainment.