Photo: Spiketooth (CC BY-SA 3.0) — via Wikimedia Commons
Hillstream Loach (Sewellia lineolata)
A living suction cup from Vietnam's rushing mountain streams: this flat, patterned algae-grazer demands ice-cold, turbocharged flow that most community tanks can't match.
Will it live with a Hillstream Loach?
We compare each fish against your hillstream loach on temperament, size, water parameters and swimming zone. Set your tank size and filter the results.
- Agassiz's Corydoras✅ CompatiblePeaceful · 6 cm · Easy care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 22–24 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the bottom of the tank — offer enough cover so they aren't always in each other's space.
- Keep Agassiz's Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Betta✅ CompatibleSemi-aggressive · 6.5 cm · Easy care · 24–28 °C (75–82 °F)
- Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Black Skirt Tetra✅ CompatibleSemi-aggressive · 6 cm · Easy care · 20–26 °C (68–79 °F)
- Compatible on the things that matter: shared water near 20–24 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Black Skirt Tetra in a shoal of 6+ or it gets stressed and nippy.
- Blackline Rasbora✅ CompatiblePeaceful · 6 cm · Easy care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 22–24 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blackline Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Blood Red Tiger Pleco✅ CompatiblePeaceful · 6 cm · Medium care · 24–29 °C (75–84 °F)
- Compatible on the things that matter: shared water near 24–24 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the bottom of the tank — offer enough cover so they aren't always in each other's space.
- Butterfly Hillstream Loach✅ CompatiblePeaceful · 6 cm · Hard care · 18–24 °C (64–75 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Both favour the bottom of the tank — offer enough cover so they aren't always in each other's space.
- Desert Goby✅ CompatibleSemi-aggressive · 6 cm · Easy care · 18–28 °C (64–82 °F)
- Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Both favour the bottom of the tank — offer enough cover so they aren't always in each other's space.
- Diamond Tetra✅ CompatiblePeaceful · 6 cm · Easy care · 22–28 °C (72–82 °F)
- Both are peaceful, and their water overlaps around 22–24 °C — no size, zone or temperament conflicts.
- Keep Diamond Tetra in a shoal of 6+ or it gets stressed and nippy.
- Eastern Betta✅ CompatibleSemi-aggressive · 6 cm · Medium care · 24–28 °C (75–82 °F)
- Compatible on the things that matter: shared water near 24–24 °C, workable temperaments, and no predator-and-prey size gap.
- Elegant Cory✅ CompatiblePeaceful · 6 cm · Easy care · 22–28 °C (72–82 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Both favour the bottom of the tank — offer enough cover so they aren't always in each other's space.
- Keep Elegant Cory in a shoal of 6+ or it gets stressed and nippy.
- False Julii Corydoras✅ CompatiblePeaceful · 6 cm · Easy care · 22–26 °C (72–79 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Both favour the bottom of the tank — offer enough cover so they aren't always in each other's space.
- Keep False Julii Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Glass Bloodfin Tetra✅ CompatiblePeaceful · 6 cm · Easy care · 22–28 °C (72–82 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Glass Bloodfin Tetra in a shoal of 6+ or it gets stressed and nippy.
- GloFish Tetra✅ CompatibleSemi-aggressive · 6 cm · Easy care · 21–28 °C (70–82 °F)
- Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep GloFish Tetra in a shoal of 6+ or it gets stressed and nippy.
- Guppy✅ CompatiblePeaceful · 6 cm · Easy care · 22–28 °C (72–82 °F)
- Both are peaceful, and their water overlaps around 22–24 °C — no size, zone or temperament conflicts.
- Neon Dwarf Rainbowfish✅ CompatiblePeaceful · 6 cm · Easy care · 23–27 °C (73–81 °F)
- Both are peaceful, and their water overlaps around 23–24 °C — no size, zone or temperament conflicts.
- Keep Neon Dwarf Rainbowfish in a shoal of 6+ or it gets stressed and nippy.
- Odessa Barb✅ CompatibleSemi-aggressive · 6 cm · Easy care · 20–26 °C (68–79 °F)
- Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Odessa Barb in a shoal of 6+ or it gets stressed and nippy.
- Panda Loach✅ CompatiblePeaceful · 6 cm · Hard care · 18–23 °C (64–73 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Both favour the bottom of the tank — offer enough cover so they aren't always in each other's space.
- Peaceful Betta✅ CompatibleSemi-aggressive · 6 cm · Medium care · 24–28 °C (75–82 °F)
- Compatible on the things that matter: shared water near 24–24 °C, workable temperaments, and no predator-and-prey size gap.
- Pearl Danio✅ CompatiblePeaceful · 6 cm · Easy care · 20–25 °C (68–77 °F)
- Compatible on the things that matter: shared water near 20–24 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Pearl Danio in a shoal of 6+ or it gets stressed and nippy.
- Platy✅ CompatiblePeaceful · 6 cm · Easy care · 21–28 °C (70–82 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Samurai Gourami✅ CompatiblePeaceful · 6 cm · Hard care · 24–28 °C (75–82 °F)
- Both are peaceful, and their water overlaps around 24–24 °C — no size, zone or temperament conflicts.
- Slate Corydoras✅ CompatiblePeaceful · 6 cm · Medium care · 23–28 °C (73–82 °F)
- Both are peaceful, and their water overlaps around 23–24 °C — no size, zone or temperament conflicts.
- Both favour the bottom of the tank — offer enough cover so they aren't always in each other's space.
- Keep Slate Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Smaragd Betta✅ CompatibleAggressive · 6 cm · Medium care · 23–28 °C (73–82 °F)
- Peaceful + Aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Three-striped Dwarf Cichlid✅ CompatibleSemi-aggressive · 6 cm · Medium care · 23–29 °C (73–84 °F)
- Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Both favour the bottom of the tank — offer enough cover so they aren't always in each other's space.
- African Butterfly Cichlid⚠️ With cautionSemi-aggressive · 8 cm · Medium care · 22–28 °C (72–82 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Amazon Puffer⚠️ With cautionPeaceful · 8 cm · Medium care · 23–28 °C (73–82 °F)
- Your 75 L tank is below the ~120 L this pairing really wants — crowding raises aggression.
- Keep Amazon Puffer in a shoal of 6+ or it gets stressed and nippy.
- Ash Lipped Apisto⚠️ With cautionSemi-aggressive · 7 cm · Hard care · 24–29 °C (75–84 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Black Ruby Barb⚠️ With cautionSemi-aggressive · 6 cm · Easy care · 22–26 °C (72–79 °F)
- Your 75 L tank is below the ~100 L this pairing really wants — crowding raises aggression.
- Keep Black Ruby Barb in a shoal of 6+ or it gets stressed and nippy.
- Bleeding Heart Tetra⚠️ With cautionSemi-aggressive · 7 cm · Medium care · 23–28 °C (73–82 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Bleeding Heart Tetra in a shoal of 6+ or it gets stressed and nippy.
- Bright Diamond Tetra⚠️ With cautionPeaceful · 7 cm · Hard care · 24–28 °C (75–82 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Bright Diamond Tetra in a shoal of 8+ or it gets stressed and nippy.
- Buenos Aires Tetra⚠️ With cautionSemi-aggressive · 7 cm · Easy care · 18–26 °C (64–79 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Buenos Aires Tetra in a shoal of 6+ or it gets stressed and nippy.
- Colombian Tetra⚠️ With cautionSemi-aggressive · 6.5 cm · Easy care · 24–28 °C (75–82 °F)
- Your 75 L tank is below the ~114 L this pairing really wants — crowding raises aggression.
- Keep Colombian Tetra in a shoal of 6+ or it gets stressed and nippy.
- Congo Tetra⚠️ With cautionPeaceful · 8 cm · Medium care · 22–28 °C (72–82 °F)
- Your 75 L tank is below the ~120 L this pairing really wants — crowding raises aggression.
- Keep Congo Tetra in a shoal of 6+ or it gets stressed and nippy.
- Dwarf Chain Loach⚠️ With cautionPeaceful · 6 cm · Medium care · 24–29 °C (75–84 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Dwarf Chain Loach in a shoal of 6+ or it gets stressed and nippy.
- Glass Catfish⚠️ With cautionPeaceful · 8 cm · Medium care · 23–28 °C (73–82 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Glass Catfish in a shoal of 6+ or it gets stressed and nippy.
- Humpbacked Tetra⚠️ With cautionSemi-aggressive · 5 cm · Hard care · 24–28 °C (75–82 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Humpbacked Tetra in a shoal of 8+ or it gets stressed and nippy.
- Melon Barb⚠️ With cautionPeaceful · 7 cm · Easy care · 22–28 °C (72–82 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Melon Barb in a shoal of 8+ or it gets stressed and nippy.
- Morse Code Corydoras⚠️ With cautionPeaceful · 5 cm · Medium care · 23–26 °C (73–79 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Morse Code Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Rounded Filament Barb⚠️ With cautionPeaceful · 7 cm · Medium care · 22–27 °C (72–81 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Rounded Filament Barb in a shoal of 6+ or it gets stressed and nippy.
- Tiger Barb⚠️ With cautionSemi-aggressive · 7 cm · Easy care · 22–28 °C (72–82 °F)
- Your 75 L tank is below the ~95 L this pairing really wants — crowding raises aggression.
- Keep Tiger Barb in a shoal of 6+ or it gets stressed and nippy.
- Alligator Gar⛔ Not recommendedAggressive · 250 cm · Hard care · 24–28 °C (75–82 °F)
- Hillstream Loach is bite-sized to a 250 cm predatory alligator gar — it will be eaten.
- Your 75 L tank is below the ~3785 L this pairing really wants — crowding raises aggression.
- Clown Knifefish⛔ Not recommendedAggressive · 90 cm · Hard care · 24–28 °C (75–82 °F)
- Clown Knifefish (90 cm) is big enough to swallow the 6 cm Hillstream Loach whole.
- Your 75 L tank is below the ~750 L this pairing really wants — crowding raises aggression.
- Fire Eel⛔ Not recommendedSemi-aggressive · 100 cm · Medium care · 24–28 °C (75–82 °F)
- Size gap is too large (100 vs 6 cm): Fire Eel will treat Hillstream Loach as food.
- Your 75 L tank is below the ~380 L this pairing really wants — crowding raises aggression.
- Koi⛔ Not recommendedPeaceful · 90 cm · Medium care · 4–28 °C (39–82 °F)
- Size gap is too large (90 vs 6 cm): Koi will treat Hillstream Loach as food.
- Your 75 L tank is below the ~3800 L this pairing really wants — crowding raises aggression.
- Redtail Catfish⛔ Not recommendedAggressive · 120 cm · Hard care · 24–27 °C (75–81 °F)
- Hillstream Loach is bite-sized to a 120 cm predatory redtail catfish — it will be eaten.
- Your 75 L tank is below the ~5700 L this pairing really wants — crowding raises aggression.
- Spotted Gar⛔ Not recommendedAggressive · 90 cm · Hard care · 18–26 °C (64–79 °F)
- Size gap is too large (90 vs 6 cm): Spotted Gar will treat Hillstream Loach as food.
- Your 75 L tank is below the ~600 L this pairing really wants — crowding raises aggression.
- Wels Catfish⛔ Not recommendedAggressive · 300 cm · Hard care · 15–25 °C (59–77 °F)
- Wels Catfish (300 cm) is big enough to swallow the 6 cm Hillstream Loach whole.
- Your 75 L tank is below the ~20000 L this pairing really wants — crowding raises aggression.
- Wolf Cichlid⛔ Not recommendedAggressive · 72 cm · Hard care · 24–30 °C (75–86 °F)
- Wolf Cichlid (72 cm) is big enough to swallow the 6 cm Hillstream Loach whole.
- Your 75 L tank is below the ~760 L this pairing really wants — crowding raises aggression.
Compatibility is computed from each species' care data — a strong starting point, not a guarantee. Individual temperament varies, so always introduce new fish slowly and watch them.
Hillstream Loach care specs
- Care level
- Hard
- Breeding
- Medium
- Max size
- 6 cm (2.4 in)
- Min tank size
- 75 L (19.8 gal)
- Temperature
- 20–24 °C (68–75 °F)
- pH
- 6.5–7.5
- Hardness
- 4–12 dGH
- Lifespan
- 5–8 years
- Diet
- Herbivore
- Swim level
- Bottom
- Group size
- 3+ (shoaling)
- Family
- Gastromyzontidae
- Origin
- Central Vietnam — Huong, Thu Bon, Tra Khuc and An Lao river drainages (fast-flowing hill streams)
What is a Hillstream Loach?
The hillstream loach (Sewellia lineolata) is a small, torpedo-flat freshwater fish from the rapid-fire mountain streams of central Vietnam. Reaching just 6 cm (2.4 in) in adulthood, it is built like an engineering solution to fast water: a wide, depressed body, large paired fins spread horizontally like wings, and a ventral sucker formed by modified pectoral and pelvic fins that lets it cling to smooth boulders in pounding current. The tan-to-brown body is overlaid with a striking bold black reticulated — net-like — pattern, and the fin edges are tipped white, making it one of the more visually dramatic loaches in the hobby.
Also sold as the tiger hillstream loach, reticulated hillstream loach, or butterfly loach, Sewellia lineolata belongs to the family Gastromyzontidae — a specialist group of Asian torrent-adapted loaches quite distinct from the more familiar Botia hillstream relatives. It is classified as a hard species to keep, not because it is delicate in personality, but because its water-quality demands are narrow and uncompromising. Get the environment right and it is a rewarding, long-lived grazer; underestimate what it needs and it will quietly waste away.
Where do Hillstream Loaches come from?
Sewellia lineolata is endemic to central Vietnam, collected from the Huong, Thu Bon, Tra Khuc and An Lao river drainages — rivers that cascade down forested hills before flattening into the coastal plain. The habitat in those upper reaches is radically different from the still or sluggish water most aquarium fish come from: shallow, clear, fast-flowing rapids over smooth granite or sandstone bedrock, heavily oxygenated, sun-lit enough to grow thick algal mats, and cool year-round because the water drains quickly from altitude.
Understanding that origin is the single most important step in keeping this fish. The hillstream loach’s entire anatomy is an adaptation to current and rock — it was never built for a warm, still community tank, and no amount of good intentions will change that biology.
What size tank does a Hillstream Loach need?
The minimum is 75 litres (20 gal) for a group of three, and that number assumes the tank is long and shallow rather than tall — footprint matters more than volume here. A 90–120 cm (36–48 in) length tank with a relatively low water depth gives adequate horizontal run and makes it easier to create vigorous flow throughout the whole water column, not just near the filter outlet.
Equip the tank with a high-flow canister or hang-on-back filter rated well above the standard recommendation — target a turnover of 10–15 times the tank volume per hour. A supplementary powerhead or wave-maker positioned to push water across flat rock surfaces is often necessary to reach the flow speeds hillstream loaches need. Surface agitation should be strong enough to visibly ripple the water; this keeps dissolved oxygen near saturation. Use a fine sand or smooth pea-gravel substrate, and fill the tank with smooth flat stones and slate pieces — these provide grazing surfaces and resting spots in current. A sand area away from the main flow gives the fish somewhere to settle when they choose to rest.
What water parameters do Hillstream Loaches need?
- Temperature: 20–24 °C (68–75 °F). This is the single most non-negotiable parameter. Temperatures above 25 °C cause chronic stress and suppress immune function; above 27 °C the fish typically cannot survive long-term. Room temperature in a cool home is often close enough without a heater in summer, but a chiller or fan-cooled sump may be needed in warm climates.
- pH: 6.5–7.5, neutral to slightly acidic or alkaline.
- Hardness: 4–12 dGH, soft to moderately hard — matching the mineral composition of fast-flowing hill rivers.
- Dissolved oxygen: Near saturation. Strong surface agitation is the practical means; do not seal the tank tightly.
Test water regularly. Hillstream loaches are sensitive to ammonia and nitrite accumulation, and a mature, well-cycled tank with an established biofilm is strongly preferred over a newly set-up one.
What do Hillstream Loaches eat?
Diet is primarily algae and biofilm — the thin microbial layer of bacteria, diatoms, detritus and tiny invertebrates that coats hard surfaces in mature tanks. For this reason, it is strongly recommended to run the tank for at least 6–8 weeks before adding hillstream loaches, allowing rock and glass surfaces to develop a healthy algal and biofilm coating.
Supplement the natural biofilm with:
- Blanched courgette (zucchini), cucumber, or spinach weighted to the bottom
- Spirulina wafers and algae-based sinking tabs
- Repashy gel foods formulated for algae grazers
- Occasional small portions of sinking food that contains a minor protein component — they will naturally pick up tiny invertebrates in the wild
Avoid high-protein foods as a staple; hillstream loaches are herbivores and can develop digestive problems on a carnivore-leaning diet. Feed once or twice daily and remove uneaten vegetables within 24 hours to maintain water quality.
Are Hillstream Loaches aggressive — and what fish can live with them?
Hillstream loaches are peaceful toward other species. Males within the same species may spar briefly over territory — squabbles that look dramatic given the posturing involved but rarely cause injury — which is why keeping a minimum group of 3 is recommended; it dilutes male-to-male tension and produces more natural behaviour than a single fish or an all-male pair.
The compatibility challenge is not temperament but environment. The cool (20–24 °C), fast, high-oxygen water required by hillstream loaches excludes the majority of popular tropical community fish. Suitable tank mates are species that also tolerate or prefer cooler, well-oxygenated conditions:
- White cloud mountain minnows (Tanichthys albonubes)
- Celestial pearl danios (Danio margaritatus)
- Smaller danio species in general
- Dojo/weather loach (Misgurnus anguillicaudatus)
- Rosy barbs (Pethia conchonius)
Avoid bettas, discus, angelfish, guppies, and any species that needs warm, still water — the temperature mismatch alone will compromise one or both fish. For a full breakdown of compatible and incompatible pairings, see Hillstream Loach tank mates.
How do you tell male and female Hillstream Loaches apart?
Sexual dimorphism in Sewellia lineolata is subtle outside breeding condition but becomes more apparent as fish mature. Males develop a distinctively broader, more flattened head with fleshy, bumpy tubercles (small knob-like growths) on the snout — visible when the fish is examined closely from above or face-on. This appears most pronounced in males coming into breeding condition. Females are generally plumper through the mid-section when gravid (carrying eggs), and lack the prominent snout tubercles. Juveniles and sub-adults are harder to sex reliably; wait until fish are at least 3–4 cm before attempting to identify males.
How do Hillstream Loaches breed?
Breeding Sewellia lineolata in captivity is achievable and has been documented, earning a medium difficulty rating. The key triggers appear to be: a well-established tank with healthy biofilm, strong flow, clean cool water, and the presence of both sexes in a group.
Courtship involves the male closely following and positioning himself alongside the female, and spawning occurs on flat, clean rock surfaces — the eggs are adhesive and deposited in small clutches rather than scattered broadcast. Males compete for access to females and may display to each other during this period. The eggs are small and the fry, once they hatch after roughly two weeks, are tiny and require an established biofilm to graze from immediately. Separating a breeding slate or flat stone with eggs into a small, heavily oxygenated grow-out tank improves fry survival. Raising fry to juvenile size takes patience and pristine water quality.
What are common Hillstream Loach diseases?
Hillstream loaches are not disease-prone when kept in appropriate conditions, but their sensitivity means that water-quality lapses hit them harder than hardier species. Common issues include:
- Ich (white spot disease): White pinhead spots on fins and body, caused by the parasite Ichthyophthirius multifiliis. Elevated temperature is the standard treatment method used with most tropicals, but this conflicts directly with hillstream loach requirements — prevention through quarantine of new fish and equipment is essential.
- Bacterial infections / fin erosion: Usually secondary to stress from poor water quality, high temperatures, or injury from territorial sparring. Strong flow and clean water are the primary preventives.
- Intestinal issues: Associated with inappropriate high-protein diets or overfeeding. Maintain a biofilm-rich, plant-based feeding regime.
- Oxygen starvation: Not a disease but a common cause of rapid decline — check that surface agitation and flow remain strong, especially in warm weather when dissolved oxygen drops.
Quarantine all new additions for at least 2–4 weeks before introducing them to an established tank. Maintain excellent water quality and stable cool temperatures as the first line of defence against all health problems.
Health note: Disease diagnosis and treatment in hillstream loaches is complicated by their unusual temperature requirements. Confirm symptoms against a reputable aquatic veterinary or specialist fish-health source before medicating — some standard treatments are not compatible with cool-water setups or with the delicate biofilm these fish depend on.
How long do Hillstream Loaches live?
A well-kept Sewellia lineolata lives 5–8 years in an aquarium that meets its environmental demands — a respectable lifespan that reflects how durable these fish are when the fundamentals are correct. The catch is that the fundamentals are genuinely demanding: consistent cool temperatures, perpetual strong flow, near-saturated dissolved oxygen, and a biofilm-rich environment take more planning than a standard tropical setup. Fishkeepers who invest in a purpose-built hillstream biotope tank frequently report their loaches thriving for the full duration of that range. Those who compromise on flow or temperature tend to lose fish within a year or two. Match the environment to the fish, and the hillstream loach rewards that effort generously.
Frequently asked questions
Why does the hillstream loach need fast water flow in an aquarium?
In the wild, Sewellia lineolata lives in shallow, boulder-strewn rapids that are almost fully saturated with oxygen. Their flattened body and sucker-like pectoral fins are built for clinging to rocks in current — without strong flow and high dissolved oxygen (aim for turnover of 10–15× the tank volume per hour), they become lethargic and decline. A HOB or canister filter angled to break the surface, plus a wave-maker or powerhead, is the minimum setup.
Can hillstream loaches live with tropical community fish?
Only if the community fish can tolerate the same cool, fast conditions — which rules out most tropicals. Good tank mates include white cloud mountain minnows, celestial pearl danios, smaller danio species, and dojo loaches, all of which prefer 20–24°C. Avoid bettas, discus, or any species that needs still, warm water. Within the species, males may scuffle but rarely cause injury; a group of three or more spreads aggression.
What you need to keep a hillstream loach
The baseline is a heated, filtered 75 L+ tank: a reliable heater to hold 20–24 °C (68–75 °F), a gentle filter that won't batter a hillstream loach in the current, and a tight-fitting lid. Cycle the tank fully before adding any fish.
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