Banded Borneo hillstream loach

Where they come from

Banded Borneo hillstream loaches (Gastromyzon fasciatus) come from fast, rocky streams in Borneo. Picture shallow water ripping over smooth stones with tons of oxygen and a constant supply of algae and biofilm. That whole "stuck to the rocks" look is basically their entire lifestyle.

If you try to keep them like a regular community bottom-dweller, they usually fade over time. If you build the tank like a little river, they turn into one of the coolest fish you can watch day-to-day.

Setting up their tank

Flow and oxygen are the game here. I have had the best results treating them like a "river tank" fish first and an "algae eater" second. They want moving water, lots of surface agitation, and hard surfaces to graze.

• Tank size: 20 long works for a small group, but 30-40 gallons is way easier to stabilize and gives them more grazing space.
• Flow: strong. A good canister or HOB plus a powerhead aimed along the length of the tank helps. You want visible current, not just a gentle ripple.
• Oxygen: run an airstone or crank surface agitation. Warm water plus low oxygen is where they crash.
• Substrate: sand or fine gravel is fine, but the real estate that matters is smooth river rocks, cobbles, and flat stones.
• Hardscape: stack rocks to create lots of "parking spots" in the flow and calmer pockets behind them.
• Plants: optional. If you use them, pick stuff that tolerates current (Anubias, Java fern, Bolbitis) and tie it to rocks/wood.
• Temperature: cool to mid-70s F is my comfort zone for them. They can handle warmer for a bit, but they look stressed long term.
• Parameters: they are not super picky about pH, but they hate dirty water. Keep nitrate low and stable.

One underrated tip: build in algae time. I like to set up the tank, get it stable, then let rocks and glass grow a nice film before adding them (or at least before expecting them to look their best). A too-clean tank with shiny rocks usually means they are living off whatever extra food you toss in, and that is not the same as grazing all day.

What to feed them

They are grazers. They spend the whole day rasping biofilm, soft algae, and tiny critters off surfaces. The best feeding plan is a mix of natural grazing plus targeted foods that sink and stay put in current.

• Staples: algae wafers or high-quality sinking tablets (break them into pieces and tuck them between rocks so they do not blow away).
• Veg: blanched zucchini/cucumber, green beans, spinach. Clip it down or wedge it under a stone.
• Biofilm boosters: repashy-style gel foods work great because you can smear a bit on a rock and they will graze it naturally.
• Protein: small amounts of frozen foods like baby brine shrimp, daphnia, cyclops, or chopped bloodworms. Think "snack," not "main diet."

Watch their bellies more than the food label. A well-fed Gastromyzon has a gently rounded belly, not pinched-in. If you see them getting thin while other fish look fat, the food is getting stolen or blowing around where they cannot work on it.

How they behave and who they get along with

They are peaceful, but they are not pushovers with their own kind. You will see little "dance-offs" and shoving matches over favorite rocks. It looks dramatic, but it is usually harmless as long as the tank has enough surface area and sight breaks.

• Good tankmates: small, fast fish that like flow (danios, white cloud mountain minnows in cooler setups, small rasboras), and other peaceful river species.
• Also works: small shrimp and snails, as long as your other fish do not snack on them.
• Avoid: big, slow, or aggressive fish, and anything that wants warm, still water (they make the loach choose between comfort and oxygen).
• Avoid: strong food hogs that park on wafers (some larger loaches, big plecos, or boisterous barbs) unless you have lots of feeding spots.

Breeding tips

They do breed in aquariums, but it is not the kind of fish where you set up a mop and collect eggs every morning. Most hobbyist spawns seem to happen in mature, stable river tanks with lots of biofilm, strong flow, and plenty of hiding cracks between rocks.

• Start with a group so you have both sexes. Sexing is subtle and often easiest once they are adult and well-fed.
• Use a rock pile with lots of crevices. The more "maze" you build, the better the odds of fry surviving.
• Keep the tank mature and steady. Sudden changes tend to set them back.
• Feed heavy (but clean) for a few weeks: lots of grazing surfaces plus small protein feeds.
• If you get fry, they need micro foods and biofilm. Let algae grow on stones and consider adding powdered fry foods or infusoria-style foods.

Common problems to watch for

Most issues with Gastromyzon fasciatus come from the tank being too warm, too still, too new, or too dirty. They are "advanced" mostly because they punish shortcuts.

• Gasping or hovering in high-flow areas: often low oxygen, especially at higher temps. Add surface agitation and drop the temp a bit.
• Slow weight loss: not enough grazing or food is getting stolen. Add more feeding stations and grow more biofilm.
• Sudden deaths after purchase: shipping stress plus low oxygen. Quarantine with strong aeration and hiding spots, and keep meds gentle.
• Ich and other parasites: they can get it like any fish, but treat carefully. Boost oxygen during treatment and avoid overdosing.
• Mouth or belly redness: can be from abrasions on rough decor or bacterial issues in dirty tanks. Use smooth stones and step up water changes.

If you want a simple success check: they should be out in the open, plastered to rocks, grazing constantly, with full bellies and strong, even breathing. If they are hiding all the time or clinging near the surface, something about flow, oxygen, or stability is off.