FishFreshwaterAdvanced
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Reticulated Hillstream Loach / Tiger Hillstream Loach
Sewellia lineolata
Resembling a tiny stingray, this hydrodynamic loach thrives in pristine, torrential hillstream rapids. It continuously grazes on boulder biofilm and requires intense water flow to survive.
Water Temperature
20 - 24 °C
pH Value
6.5 - 7.5
Water type
Freshwater
Tank level
Bottom
Adult size
6 cm
Minimum tank volume
>= 60 L
Minimum group
>= 1
GH
5 - 15 dGH
KH
2 - 7 dKH
TDS
95 - 295 ppm
Conductivity
148 - 461 uS/cm
Species description
Geographical Origin and Habitat: Central Vietnam hill and mountain streams. Lives directly in the riffles and small waterfalls, scraping submerged boulders under the forest canopy.
Taxonomy and Morphology: Gastromyzontidae (6 cm). An evolutionary marvel: body flattened into a hydrodynamic suction cup. Fused horizontal pectoral and pelvic fins form a continuous skirt resembling a freshwater stingray. Fast water flowing over its body actively pins it to the rocks.
Social Behavior: Diurnal and territorial. Must be kept in groups (4-5+). Males engage in spectacular, harmless pushing contests ('capping') trying to cover each other with their fin skirts to establish feeding hierarchies.
Coloration and Sexual Dimorphism: Stunning maze-like or tiger-striped reticulated pattern of gold, beige, and pitch black. Viewed from above, males have 'square' shoulders due to nuptial tubercles; females are smoothly aerodynamic and wider.
Care, breeding and tankmates
Aquarium Setup: Requires a 100+ liter 'Hillstream' setup. Torrential flow via wavemakers (15-20x tank turnover per hour). Use smooth, round boulders of various sizes and high lighting to grow green algae patches on the rocks for grazing.
Diet and Feeding: Biofilm/Aufwuchs grazer and micro-predator. Scrapes rocks/glass non-stop. Doesn't eat hair algae, but the microorganisms inside it. Must be supplemented with sinking Repashy gels smeared on stones, high-quality bottom wafers, and frozen bloodworms.
Water Quality: Zero tolerance for ammonia/nitrite or low oxygen. pH 6.5-7.5. Cool to mild temperatures: 20-24°C. At 26°C+, they suffer severe respiratory distress unless oxygenation is massive.
Compatibility and Cohabitation: Only for hillstream setups (Danios, White Clouds, Stiphodon gobies). Unfit for Discus/Angelfish tanks due to completely opposite temperature and current needs.
Aquarium Breeding: Spontaneous in proper setups. Eggs drop into coarse river gravel where parents cannot reach them. Fry emerge fully formed months later.
Risks and Diseases: Starvation in new, sterile tanks. Asphyxiation in hot, slow-moving water. Lethal sensitivity to standard aquarium medications due to lack of scales.
Geographic Origin and Distribution
Central Vietnam hill and mountain streams. Lives directly in the riffles and small waterfalls, scraping submerged boulders under the forest canopy.
Origin
North AmericaSouth and Southeast AsiaEast Asia
Fish profile
- Temperament
- Semi-aggressive
- They are highly active, peaceful towards other species, and immensely entertaining to watch. Males will squabble over prime grazing real estate, but these disputes never result in injury. They are entirely harmless to both plants and community fish.
- Diet
- Omnivore
- Their primary diet consists of the aufwuchs—the biofilm and algae growing on rocks and glass. This must be supplemented with high-quality sinking algae wafers, repashy gel food, and occasional blanched vegetables. A mature tank with natural algae growth is essential before adding them.
- Life expectancy
- 5-10 years
- Under proper husbandry and optimal conditions, the Reticulated Hillstream Loach can live for 5 to 10 years in captivity. Keeping the water cool and saturated with oxygen is essential to ensure their health and longevity. Many premature deaths in aquariums are caused by high summer temperatures and oxygen deprivation.
- Adult size
- 6 cm
- The catalog's scalar value is 6 cm. The FishBase SPECIES table (v25.04 snapshot) source reports a maximum adult measurement of 5.66 cm for this species, recorded as standard length (SL). The taxonomic record consulted is Sewellia lineolata (v25.04); male or unsexed record. These figures are not interchangeable: the first is the profile's editorial reference, whereas the second is a published maximum under a specific measurement convention; differences among sources can reflect sex, population, life stage and measuring method.
- Sex ratio
- Group
- They can be kept in mixed groups without issues, but having more females than males can reduce territorial squabbling. Males can be territorial with each other, engaging in harmless parallel swimming battles to establish dominance. A group of five or more is highly recommended.
- Feeding frequency
- Twice daily
- Because they are continuous grazers, they should have constant access to biofilm and algae. Supplemental feeding of wafers or gel food can be offered once a day. Ensure that the food sinks and stays anchored in the high current.
- Bioload
- The Reticulated Hillstream Loach has a very low bioload. They are small and process primarily algae and biofilm, meaning they produce minimal waste. However, they require pristine water quality to survive, so excellent filtration is still mandatory.
- Flow
- Stagnant
- They are adapted for life in torrential streams and absolutely require high water flow. A specialized river-manifold system or strong powerheads must be used to create a unidirectional current. Extremely high dissolved oxygen levels are critical for their survival.
- Reproduction
- Oviparous
- Breeding frequently occurs spontaneously in well-maintained setups with the correct riverine conditions. Males will establish territories and perform intricate dances to attract females. The fry will hide in the substrate and feed on microscopic organisms without needing special parental care.
- Compatibility & tankmates
- They are peaceful and excel in community tanks specifically designed to simulate fast-flowing rivers. Good tank mates include White Cloud Mountain Minnows, Danios, and small peaceful gobies. Do not keep them with large, aggressive fish or species that cannot tolerate high flow rates.
- Tank level
- Bottom
- They spend their time on smooth surfaces across all levels of the tank, including the glass and large rocks. They do not swim freely in the water column very often. Providing smooth river stones is essential for them to graze and rest upon comfortably.
Scientific Parameters & Models
FishBase
Window to the official scientific data of the species
Data synced on: 06/15/2026
- Trophic level
- 2.7 ± 0.24 se
- Phylogenetic uniqueness (PD50)
- 0.5001
- Bayesian Length-Weight
- a = 0.00646, b = 3.11
- VulnerabilityLow vulnerability (10 / 100)
Image gallery
Licensed images linked to the species or, when marked, to the closest representative taxon.
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