Reticulated Hillstream Loach Care Guide

The reticulated hillstream loach is a cool-water, high-flow, high-oxygen river fish, not a still, warm community algae-eater. It is a mature-tank aufwuchs grazer that slowly starves in a clean, new, or low-flow tank, and almost every care rule traces to one origin fact: it comes from shallow, fast, oxygen-saturated mountain headwaters.

Reticulated Hillstream Loach at a glance

The sourced figures the welfare engine uses to judge Reticulated Hillstream Loach — the parseable key facts.

Where it comes from

Sewellia lineolata comes from the cool, fast mountain headwaters of central Vietnam, with reports from the Mekong around the Khone Falls in Laos. Seriously Fish describes its habitat as shallow, fast-flowing, highly-oxygenated headwaters of riffles and runs over bedrock, sand, gravel and jumbled boulders, with documented water velocities from 0.2 to over 1 metre per second. That rheophilous, current-loving home is the single most important biotope fact, and it dictates the tank. Over-1-metre current means strong flow is mandatory, a river tank with powerheads rather than a still community tank. Highly oxygenated means high dissolved oxygen is non-negotiable, and the scaleless body is acutely sensitive to low oxygen and to heat, since warm water holds less of it. Boulders coated in benthic algae are both the habitat and the food. Cool headwaters mean a cool tank of about 20-24 C, not 26-28 C tropical, so a heater is often unnecessary or set low and the real risk in most homes is the tank being too warm. FishBase classes it as tropical, but it is a cool-running mountain-stream tropical, the distinction that trips up most buyers.

Did you know?

• It is a living suction cup: its broad pectoral and pelvic fins fuse into a suction disc that lets it cling to bare rock, and to aquarium glass, in current strong enough (over 1 metre per second in the wild) to sweep most fish away.
• Origin dictates everything: cool temperature, ferocious flow, high oxygen, smooth rocks and a biofilm diet all trace to the shallow, fast, oxygen-saturated mountain headwaters of central Vietnam.
• It eats the rocks, sort of: its food is aufwuchs, the living film of algae, diatoms, bacteria and micro-invertebrates coating submerged stones, not conventional fish food.
• It is one of the easiest loaches to breed, but mostly by accident, spawning spontaneously in a mature, high-flow tank rather than on demand.
• It is surprisingly long-lived: a roughly 6 cm fish that commonly reaches 8-10 years.
• IUCN lists it as Vulnerable (assessed 2010), a reason to favour captive-bred stock over wild-caught.

Tank size — and why

About 30 US gallons (roughly 114 L) is the sensible floor for a small group, with a 40-gallon long or a 55 markedly better; Seriously Fish frames it as a footprint of at least 75 by 30 cm. The reason is footprint, flow and oxygen rather than swim volume: although it is a small fish of around 6 cm, it needs length to run strong end-to-end current and oxygenate a large surface, floor and rock area for a grazing group to hold non-overlapping patches, and water volume to keep cool, clean, oxygen-rich water steady. Strongly prefer a long, shallow tank over a tall one, because this is a benthic rock-clinger to which depth is nearly useless and surface area and laminar flow are everything.

As a guide, a 30-gallon tank comfortably suits a starter group of about 8–12 Reticulated Hillstream Loach. As floor-dwelling shoalers they want bottom area, not water column, so a bigger group or added tankmates pushes you toward a larger footprint rather than fitting in alongside.

How big does it really get?

Full-grown Reticulated Hillstream Loach reach about 6 cm (2.4 in) long, but they are usually sold at only about 2.5 cm (1 in) — a typical shop size (estimate). At full size, Reticulated Hillstream Loach needs roughly a 30-gallon tank, about 76 cm long; a common 10-gallon starter kit is only about 51 cm.

Adult size is sourced; the shop size is a typical-juvenile estimate; tank length is approximate for a standard 30-gallon aquarium.

Water parameters in practice

Temperature is the welfare crux: this fish belongs at the cool end, about 20-24 C, and most home tropical tanks at 25-27 C are too warm, stressing it and lowering dissolved oxygen at the same time. In many climates it needs no heater or a low setpoint, and in hot rooms a fan or chiller may be needed in summer. Aim for pH 6.5-7.5 (tolerated roughly 6.0-7.8) and soft to moderately hard water, about 1-10 dGH; stability beats precision. The two parameters that truly matter are high dissolved oxygen, which is non-negotiable, and pristine water quality, since the scaleless, oxygen-hungry body has little tolerance for the dissolved-organic load of a dirty or under-filtered tank. Keep ammonia and nitrite at zero in a cycled, mature tank.

Diet & feeding

This is the make-or-break section. In the wild much of its diet is benthic algae plus associated micro-organisms, that is aufwuchs: the living film of algae, diatoms, bacteria and tiny invertebrates coating submerged rocks. It is a specialist grazer, and in a mature, algae-rich, high-flow tank it grazes constantly across rocks, glass, wood and leaves. In a clean, new, or low-flow tank it slowly starves, because biofilm does not grow fast enough in low-flow conditions. But algae alone is not enough either: most tanks do not produce sufficient biofilm, so supplemental feeding is required, especially in groups. Offer Repashy-type gel foods, sinking algae or spirulina wafers, frozen spirulina brine shrimp, blanched vegetables such as courgette, cucumber and spinach, and occasional frozen bloodworm or daphnia. It is a slow, deliberate grazer easily out-competed by fast tankmates for prepared food, so drop sinking food where the loaches are and feed after lights-out if faster fish strip the tank. Only add these fish to a tank that has run for months with visible algae, then keep feeding it; do not assume the tank feeds itself.

Gear & setup

Build a river tank around the loach. Flow is the headline spec: the most commonly cited target is about 10-15 times tank volume per hour in turnover, with sources ranging from 8-10 times up to the high teens, achieved with powerheads, a river or manifold setup, or a dedicated hillstream tank in addition to filtration, aiming for a visibly agitated surface. A blunt field test: if you cannot feel the current with your hand in the tank, it is not enough flow. Use smooth, flat river rocks and pebbles over fine sand or smooth gravel, the load-bearing feature being plenty of smooth, biofilm-covered rock surface to graze, since these fish spend most of their time on rock surfaces rather than in open water. The tank must be mature, with established algae and biofilm, before the fish go in; a new or sterile tank is a slow death sentence. Keep it covered, as active fish in strong current can be displaced and will climb above the waterline on glass.

Temperament & behaviour

Peaceful toward other species and not generally aggressive toward dissimilar-looking fish, but intraspecific interaction is not zero. Seriously Fish calls them territorial to an extent with dominance battles; Aquarium Co-Op describes males scuffling, circling and trying to get on top of one another with no bodily harm done; other sources call them mildly territorial, and warn that in a pair the dominant fish may bully the weaker. These are harmless display and jostling contests over grazing real estate rather than injurious fighting, and they dilute across a group. Plenty of rock surface, strong flow and a mature food supply turn squabbles into harmless display, while cramped, low-flow or food-scarce tanks turn the same drive into chronic harassment of subordinates.

Group & social needs

Social and best in a group. Seriously Fish suggests six or more for the most natural behaviour, while several care sources advise keeping either one alone or three or more and specifically avoiding a pair, because the stronger fish may bully the weaker. The practical synthesis is to keep one alone or three-plus, ideally six-plus, and specifically avoid keeping exactly two. The territoriality dilutes across a larger group and spreads the dominant fish's attention.

Compatible tank mates (preview)

A short, engine-cleared shortlist — the species TankStocking's welfare engine clears with Reticulated Hillstream Loach and that suit its size and temperament best. Tap any to load the pairing in the planner.

• Amano Shrimp — Peaceful temperament, similar adult size.
• Bamboo Shrimp (Wood/Fan Shrimp) — Peaceful temperament, similar adult size.
• Black Neon Tetra — Uses the midwater zone, peaceful temperament, similar adult size.

A note on the shrimp and snails here: Reticulated Hillstream Loach is peaceful and generally invertebrate-safe — but almost any fish will take very small shrimplets given the chance, so give shrimp dense cover (moss, leaf litter) if you want a colony to grow, rather than expecting every baby to survive.

This engine-cleared shortlist is Reticulated Hillstream Loach's tankmate surface for now — a dedicated tank-mates guide can follow for high-demand species.

Breeding & sexing

Seriously Fish calls it arguably the easiest of all loach species to breed in aquaria, but it usually happens spontaneously in a well-established, well-fed, high-flow tank and is hard to do deliberately. It is an egg-layer and substrate spawner rather than a bubble-nester or mouthbrooder, with eggs depositing and developing in the gravel among rocks. Triggers are raising the temperature to about 25-26 C and large cool water changes that simulate seasonal rains, in a mature tank with strong flow. Sexing is subtle but reliable in mature fish: males develop rows of small raised tubercles, or fences, on the first few pectoral-fin rays and have a squarer, more angular snout that sticks out from the body, while females have a broader head and plumper body with the snout running almost continuously with the pectoral fins. Fry are tiny and need infusoria, then microworms or baby brine shrimp, plus the aufwuchs of the established tank. Primary sources do not publish a reliable per-spawn egg count.

Lifespan

Husbandry sources converge on about 8-10 years with good care, with a wider 5-10 range cited in some general guides, making this a genuinely long-lived nano-class fish and a real long-term commitment for a 6 cm grazer. Neither Seriously Fish nor FishBase publishes a maximum-age figure. What shortens it: chronic warmth, low oxygen, poor water quality, weak flow, and slow starvation in a tank with insufficient biofilm and no targeted feeding. Because the body is scaleless, it is also unusually sensitive to medications and chemicals and to dissolved-organic build-up.

Common mistakes

• Putting it in a warm, still community tank, the number-one fatal mistake. It is a cool (about 20-24 C), fast-flowing, high-oxygen river fish, not a 26-28 C tropical community fish; do not let the temperature drift up to tropical.
• Adding it to a new or sterile tank, which means slow starvation. It grazes aufwuchs and biofilm, so add it only to a mature tank with visible algae and keep feeding it.
• Not enough flow or oxygen. A normal filter is usually too weak; it needs strong current of about 10-15 times turnover plus a powerhead or river setup and visible surface agitation.
• Treating algae as a complete diet. They cannot survive on algae alone, so supplement with gel food, wafers, blanched veg and occasional frozen foods.
• Keeping exactly two. A pair often becomes bully-and-victim, so keep one alone or three or more, ideally six-plus.
• Overheating in summer or over-medicating. Cool-water plus scaleless means watching for heatwaves with a fan or chiller and dosing medications conservatively.
• Buying mixed or mislabelled hillstream loach stock without knowing the species, or buying obviously dyed or painted specimens.

Signs of trouble

• Leaving the rocks and hanging at the surface or near the outflow, a classic sign of low oxygen or overheating.
• A thinning body and sunken belly, the silent starvation of a fish in a clean, new, or low-flow tank; often misread as old age.
• Loss of suction grip and lethargy.
• Loss of appetite or visibly failing to compete for prepared food at feeding time.
• White spots or fungal or bacterial patches, almost always secondary to heat, low oxygen or poor water quality.

Is this fish right for you?

Don't buy this fish if you cannot provide a mature, cool (about 20-24 C), high-flow (around 10-15 times turnover), high-oxygen, well-established tank of roughly 30 gallons or more with smooth biofilm-covered rocks, cool-water tankmates, and a commitment to 8-10 years of care. It is peaceful and community-safe in temperament, but only within a cool, high-flow community: it must share its cool, fast, oxygen-rich needs with its tankmates, so it cannot go into a standard warm tropical community on welfare grounds, and fast, greedy feeders will strip its food. There are no legitimate fancy colour morphs, so avoid any dyed or painted specimens, and prefer captive-bred stock, which is increasingly available and matters because the species is assessed as Vulnerable in the wild.

Bringing one home

Quarantine new stock and acclimate gently, then add it only to a mature tank with established algae, biofilm and strong flow so it has surfaces to graze from the start. Because it is scaleless and oxygen-demanding, dose any medications conservatively, often at reduced strength, and avoid copper and harsh chemical treatments.

Common questions

Are hillstream loaches cold-water or tropical fish?

Cool-water. They belong at about 20-24 C, the cool end of tropical, and most home tropical tanks at 25-27 C are too warm, stressing the fish and lowering oxygen. In many climates they need no heater or only a low setpoint.

Why is my hillstream loach starving or wasting away?

It is an aufwuchs grazer that needs an established biofilm to feed on. In a clean, new, or low-flow tank it slowly starves. Add it only to a mature, algae-rich tank and supplement with gel food, wafers and blanched veg; algae alone is not enough.

How much flow does a hillstream loach need?

A lot. Aim for roughly 10-15 times tank-volume turnover per hour with powerheads or a river setup and visible surface agitation. A good test: if you cannot feel the current with your hand in the tank, it is not enough.

How many hillstream loaches should I keep?

Keep one alone or three or more, ideally six-plus, and specifically avoid keeping exactly two, because in a pair the dominant fish tends to bully the weaker. A larger group spreads out the mild territoriality.

What can live with a hillstream loach?

Only cool-water, high-flow-tolerant, non-greedy tankmates: White Cloud Mountain minnows, danios, hardier rasboras and small tetras that accept cooler water, other hillstream loaches, shrimp, otocinclus and snails. Avoid warm-water tropicals and fast, greedy feeders.

How big do hillstream loaches get?

Small and flat, about 5.5-6.5 cm, with roughly 6.4 cm (2.5 in) the typical maximum for Sewellia lineolata. Loose general guides citing 3 inches overstate it for this species.

Sources & confidence

Sources & confidence (9 species)

These back the Reticulated Hillstream Loach figures and the previewed tank mates above. Each figure is read from the TankStocking species database (v2026.06); below is the care reference behind it and how confident we are in that data. Confidence reflects the source quality, not whether any pairing is safe. Full source list and the welfare model are on the methodology page.

• Reticulated Hillstream Loach Sewellia lineolata — Aquarium Co-Op (hillstream loaches care guide) medium confidence
• Amano Shrimp Caridina multidentata — Aquarium Co-Op amano shrimp care; Aquadiction high confidence
• Bamboo Shrimp (Wood/Fan Shrimp) Atyopsis moluccensis — Aquariadise (aquariadise.com/caresheet-bamboo-shrimp-atyopsis-moluccensis) high confidence
• Black Neon Tetra Hyphessobrycon herbertaxelrodi — Seriously Fish / Aqua-Fish (Hyphessobrycon herbertaxelrodi) high confidence
• Black Phantom Tetra Hyphessobrycon megalopterus — Seriously Fish (Hyphessobrycon megalopterus) high confidence
• Brilliant Rasbora Rasbora einthovenii — Seriously Fish (seriouslyfish.com/species/rasbora-einthovenii) high confidence
• Bronze Corydoras Corydoras aeneus — Seriously Fish (seriouslyfish.com/species/corydoras-aeneus) high confidence
• Cardinal Tetra Paracheirodon axelrodi — Seriously Fish (seriouslyfish.com/species/paracheirodon-axelrodi) high confidence
• Checker Barb Oliotius oligolepis — Seriously Fish — Oliotius oligolepis (https://www.seriouslyfish.com/species/oliotius-oligolepis/) high confidence

Care-guide sources (7)

This guide synthesises the references below; where they disagree, the range and the disagreement are noted in the text above. The figures in the key-facts box are read from the TankStocking species database (v2026.06). Full welfare model on the methodology page.

• Seriously Fish — Sewellia lineolata (Reticulated/Tiger Hillstream Loach)
• FishBase — Sewellia lineolata
• Aquarium Co-Op — Hillstream Loach (species page)
• Aquarium Co-Op — Care Guide for Hillstream Loaches (general)
• AquariumStoreDepot — Hillstream Loach Care Guide (general)
• AquariumStoreDepot — Reticulated Hillstream Loach (species page)
• Tropical Treasures Wyo — Hillstream Loach Care Guide (Sewellia lineolata & related)

More on Reticulated Hillstream Loach

Related guides on TankStocking — each scored by the same welfare engine as the planner.

This care guide is a sourced planning reference, not veterinary advice — individual fish, filtration and maintenance all matter. Cycle the tank, test your water, and observe your fish. How TankStocking works →