Borneo Sucker Hillstream Loach (Gastromyzon borneensis)

Choose a Borneo sucker for a cool, fast-flowing river tank

The Borneo sucker is a hillstream loach of the genus Gastromyzon, a group of fishes found only on the island of Borneo. This fish is sold as Gastromyzon borneensis (Günther, 1874), which FishBase records from northern Borneo, where it lives on the bottom of swift-flowing water and reaches up to 10 cm standard length (measured without the tail). Its head and body are flattened, its paired fins spread out horizontally and its pelvic fins are joined, so the whole underside works like a broad sucker that holds the fish against the current while it grazes.

Several trade names are attached to these fish: Borneo sucker, Hong Kong pleco, butterfly loach and simply hillstream loach. Despite the “pleco” name it is not a catfish. It belongs to the hillstream loach family Gastromyzontidae, which older books and some care sheets still place in Balitoridae. FishBase lists G. borneensis as Near Threatened on the IUCN Red List (assessed in December 2018).

Decide whether your aquarium suits a river fish

Seriously Fish rates every Gastromyzon species it profiles as “Moderate” to keep. That rating comes with clear conditions: clean, well-oxygenated water with strong flow, cool temperatures and plenty of grazing surfaces, which most standard community aquariums do not provide. If you can build that river set-up, the Borneo sucker is a fascinating fish to watch as it glides over stones and holds position in the current.

Browse our loaches and oddball fish or the wider loaches and algae eaters category to compare other flow-loving species before you decide. Some gallery images are representative, so colours and markings can look slightly different on the live fish.

Know what one Borneo sucker purchase supplies

One purchase quantity supplies one live Borneo sucker in the single standard size we offer. The fish is not sexed. The photographs show the type of fish, not the individual you will receive, so markings and body shape can differ from the gallery images.

Expect a mixed-species batch

Seriously Fish notes that shipments labelled “Borneo sucker”, “Hong Kong pleco” or “butterfly loach” often contain more than one Gastromyzon species, and sometimes the similar-looking Beaufortia kweichowensis. Several Gastromyzon form look-alike pairs that are easily confused even by specialists. We sell this fish under the name G. borneensis, but if you buy several they may not all be the same species, and adult size can range from about 4 cm to 10 cm standard length depending on which species you receive.

• One unit: one Borneo sucker, sex not specified.
• Four units: the smallest group Seriously Fish recommends for Gastromyzon.
• More than four: only when the base and the filtration give every fish its own grazing area.

Prepare the aquarium fully before you order and check our delivery and Live Arrival Guarantee information for dispatch days. A river tank needs time to grow the algae these fish depend on, so the delivery date should be the last step of the plan, not the first.

Plan the aquarium around a 10 cm adult

Plan for the adult size, not the size that arrives. Seriously Fish suggests different minimum bases for different Gastromyzon: 60 × 30 cm for the smallest species of 40–50 mm, 75 × 30 cm for mid-sized species, and 120 × 30 cm for the largest, which reach 95–100 mm standard length. Because FishBase records G. borneensis at up to 10 cm, we recommend a base of at least 120 × 30 cm for a group.

The OATA hillstream loach care sheet gives a lower floor of 80 litres for a small group of hillstream loaches, which it describes as growing to about 6 cm. The larger base is the safer plan for a fish that may reach 10 cm, and it also leaves room to build a fast end and a calmer end in the same aquarium.

Run a three-step space check

1. Measure the base: length and front-to-back depth matter more than height, because these fish live on the bottom, on stones and on the glass.
2. Count the whole group: plan for at least four Borneo suckers plus every other fish in the aquarium at its adult size.
3. Check the flow path: the current needs a clear run along the tank, without a wall of décor that turns it into dead water.

Our tank volume calculator works out the litres of any aquarium, which you need for the filter turnover described below. Fit a tight lid as well: Gastromyzon can climb the glass, and both Seriously Fish and OATA advise a secure cover. Close the gaps around filter pipes and cables too.

Build a river layout with strong, steady flow

Copy the stream, not a planted community tank. Seriously Fish describes the genus as obligate dwellers of swift, shallow streams with clear, oxygen-saturated water, from sea level up to 1,350 m. They live in riffles and runs over gravel, rock, boulders and bedrock coated in biofilm, often in partial or full shade, and aquatic plants are uncommon there. They face into the current and shelter along the sides of rocks or underneath them.

Divide the base into riffle, rest and grazing zones

Use sand, smooth gravel or a mix as the substrate (OATA advises smooth material to protect the skin) and top it with rounded river stones. Seriously Fish recommends only aged driftwood, because new wood leaches tannins, and suggests plants such as Microsorum (Java fern), Crinum and Anubias, which cope with flow and grow algae on their leaves. Bright lighting helps algae and micro-organisms cover the rocks.

For flow, Seriously Fish recommends an oversized filter turning the water over 10–15 times an hour, with powerheads or airstones as needed, and TFH Magazine recommends a strong current that runs in one direction if possible. OATA suggests a powerhead directed from one side. As a worked example, a 120 × 30 × 30 cm aquarium holds about 108 litres, so 10–15 turnovers means roughly 1,080–1,620 litres per hour of real flow. Treat a filter’s rated output as a guide and check the real flow once media and pipework are in place.

Keep the water cool, clean and full of oxygen

Hold the temperature steady in the cool tropical range. Seriously Fish gives 20–24°C for most Gastromyzon, OATA gives 18–24°C for hillstream loaches, and TFH Magazine reports that these fishes enjoy cool water of around 25°C. We aim for the 20–24°C range where the sources overlap. Seriously Fish adds that warmer water is tolerated only if dissolved oxygen stays high. Warm water holds less oxygen, so in a UK summer heatwave add aeration before the room heats up rather than after the fish start breathing hard.

Read habitat values separately from waste readings

No source publishes water values for G. borneensis itself, so these are genus-level and group-level figures. OATA warns that hillstream loaches are sensitive to even small amounts of ammonia and nitrite, and TFH Magazine adds that they cannot handle excessive nitrate. Hardness and pH vary widely across UK tap supplies, so test your own water and compare it with our water matcher before you buy. If the terms are new, our water chemistry guide explains what each reading means and how to keep it stable.

Filter hard and change water every week

A river tank looks clean but needs the same discipline as any aquarium. OATA advises a 25% partial water change at least once a week, siphoning solid waste from the substrate, treating new water with tap-water conditioner and testing the water at least weekly. Because the fish rely on strong flow for oxygen, filter care is also oxygen care.

Follow a weekly maintenance sequence

1. Test ammonia, nitrite, nitrate, pH and temperature before you change anything.
2. Change 25% of the water, matching the temperature of the new water closely.
3. Treat the new water with a conditioner that removes chlorine and chloramine.
4. Siphon debris from between the stones, but leave the algae film on the rocks themselves.
5. Check powerhead and filter intakes for blockages, because reduced flow quickly means reduced oxygen.
6. Rinse filter sponges in removed tank water, never under the tap, to protect the filter bacteria.

Seriously Fish advises leaving biofilm on every surface except, if you wish, the front glass, because for these loaches it is food. Aim for balance: enough algae to graze, not so much that it smothers plants or blocks the view. Our guide to understanding aquarium filtration explains how flow, media and bacteria work together, which helps when you plan a filter strong enough for a river tank.

Let it graze, then top up with measured meals

FishBase records G. borneensis feeding on small invertebrates, algae and bottom detritus, and Seriously Fish describes the genus as rasping mainly algae and micro-organisms from hard surfaces. Diatoms and soft green algae are preferred over tough black brush algae. The best long-term food source is a mature aquarium with algae-covered rocks, topped up with prepared foods.

Build one day’s measured feeding

• Grazing: algae and biofilm on rocks, wood and glass, available all day.
• Prepared food: a sinking algae wafer or catfish pellet, sized so the group finishes it, as OATA suggests.
• Vegetables: small pieces of fresh vegetable, which OATA lists as a useful extra; blanch them so they sink.
• Live or frozen food: daphnia, bloodworm or brine shrimp now and then. TFH Magazine calls meaty foods a treat, never a staple, and Seriously Fish warns that too much protein may cause internal problems.
• Tidy-up: remove uneaten prepared food after about an hour, as OATA advises.

If the stones are being stripped bare, Seriously Fish suggests growing algae on spare stones in a bright “nursery” tank or tub and rotating them into the aquarium. It also mentions homemade gel foods bound with vegetables and Spirulina.

Watch the belly through the front glass: a Borneo sucker in good condition has a rounded underside. Seriously Fish notes that wild-caught or poorly kept fish often arrive thin and need a constant supply of suitable food, without competitors, to recover.

Introduce it to a mature, settled aquarium

Seriously Fish advises never adding Gastromyzon to a biologically immature set-up, because they need stable conditions and feed on biofilm that only grows with time. Have the flow running, the stones coloured with algae and the readings stable before delivery. TFH Magazine notes that these fish cope poorly with long journeys, so plan to be at home to unpack them promptly.

Use a first-week checkpoint plan

Our guide to acclimatising new fish explains the floating-bag method that OATA recommends, step by step. Add fish gradually: OATA warns that adding too many at once overloads the filter bacteria and causes ammonia and nitrite to rise, which hillstream loaches tolerate poorly.

Watch the group and act on changes

OATA describes a healthy hillstream loach as having clear, bright eyes, undamaged fins, intact scales, no ulcers or bumps, normal swimming and steady breathing. Learn what normal looks like for your group in the first month, so later changes stand out.

Pair each observation with an action

Do not diagnose a disease from one sign alone: overheating, low oxygen and ammonia can all look similar. Record the reading, the sign and any recent change, such as a new fish or a cleaned filter, and you will usually find the cause faster.

Keep a small Borneo sucker group with room to spread out

Seriously Fish recommends keeping at least four Gastromyzon, as they form loose groups in the wild, and OATA advises groups of at least three to four hillstream loaches because they become stressed in smaller numbers. They are territorial to an extent: Seriously Fish notes that some individuals guard a favourite feeding spot from their own kind. Give every fish enough grazing surface that one individual cannot hold all the food.

Give every fish its own grazing patch

• Spread several flat stones along the current rather than building one large rock pile.
• Break sight lines with rock edges and plants, so a guarding fish cannot see the whole base.
• Drop prepared food at two or three points at once.
• Count the fish daily, ideally at feeding time, and check every belly.

In the closely related G. ctenocephalus, Seriously Fish describes adult females as heavier-bodied and often slightly larger, a difference easiest to see from above, while males carry small tubercles on the head and on the front rays of the pectoral fins. A mixed group is likely when you buy several, but it is not guaranteed.

Breeding at home is rare. OATA notes few recorded successes for hillstream loaches, while Seriously Fish reports that G. monticola, a member of the same species group as G. borneensis according to TFH Magazine, spawned repeatedly over 12 months in an unfiltered 160-litre aquarium at 24°C.

Choose tank mates that like cool, fast water

Seriously Fish describes Gastromyzon as very peaceful but notes that the choice of tank mates is limited. Companions must enjoy the same cool, fast, oxygen-rich water, and they must not beat the loaches to every scrap of food.

Screen companions with a suits and avoid table

Good starting points in our range are White Cloud Mountain Minnows, which share the cool temperature range, and stream gobies such as the Red Neon Sumatra Goby (Seriously Fish names Stiphodon among suitable genera); check each companion’s own temperature range against yours. Other river loaches such as the Marbled Hillstream Loach, the Sucker-Belly Loach and the Leveretti Hillstream Loach need very similar set-ups, but Seriously Fish advises research before mixing loach species, because some compete for the same grazing.

Our tank mates checker helps you test a planned mix before you buy, and our hillstream loach buying guide compares the river loaches we sell side by side.

Answer Borneo sucker buying questions

Is the Borneo sucker a pleco?

No. It is sometimes sold as the Hong Kong pleco, but it is a hillstream loach of the family Gastromyzontidae from Borneo, not a South American suckermouth catfish. Its flattened body and joined pelvic fins work like a sucker in fast water.

How big does a Borneo sucker get?

FishBase records Gastromyzon borneensis at up to 10 cm standard length. Batches sold as Borneo suckers can include smaller Gastromyzon species, which Seriously Fish lists at roughly 4–10 cm standard length.

How many Borneo suckers should I keep?

At least four. Seriously Fish recommends a minimum of four Gastromyzon, and OATA advises groups of at least three to four hillstream loaches. Give each fish its own grazing stones.

What size aquarium does a Borneo sucker need?

Plan a base of at least 120 × 30 cm for a group, following Seriously Fish’s guidance for the largest Gastromyzon, which reach about 10 cm. OATA’s minimum for a small group of hillstream loaches is 80 litres.

What temperature does a Borneo sucker need?

Aim for a steady 20–24°C, the Seriously Fish range for most Gastromyzon; OATA gives 18–24°C. Keep oxygen high at all times, and add aeration in warm weather.

Can a Borneo sucker live in a normal community tank?

Only if the aquarium is mature, cool and well oxygenated, with strong water flow. Many community tanks are too warm and too still, and fast feeders can leave it hungry.

What does a Borneo sucker eat?

Mainly algae and biofilm grazed from rocks, plus small invertebrates and detritus. Add sinking algae wafers, some fresh vegetables and occasional frozen daphnia or bloodworm, without overdoing protein.

Can a Borneo sucker live with goldfish?

No. OATA calls goldfish completely unsuitable company for hillstream loaches, which need fast, highly oxygenated water and a different set-up.

Consult the care references

• FishBase: Gastromyzon borneensis — accepted name, family, distribution, maximum length, habitat, diet and IUCN status.
• Seriously Fish: genus Gastromyzon — species list, minimum aquarium bases, temperature and pH ranges, trade names and mixed shipments.
• Seriously Fish: Gastromyzon ctenocephalus — habitat, flow and turnover, décor, hardness, diet, group size, tank mates, sex differences and breeding reports for the genus.
• OATA: How to look after hillstream and weather loaches — UK care-sheet water-quality limits, aquarium size, group size, feeding, maintenance and health signs.
• TFH Magazine: In Search of Borneo Suckers — field notes on habitat, species groups, flow, oxygen, feeding and transport.