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Species profile

Cow River Loach

Neogastromyzon crassiobex

Common names: Cow River Loach

Recognized speciesLoaches
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Adult size

Up to 6 cm

Typical adult length 4.2–6 cm.

Up to 6 cm

Countries of origin

  • See all stock from Indonesia
  • See all stock from Malaysia

Good fit for your tank?

Good fit for

  • Keepers able to provide at least a 60 cm aquarium with the substrate, current, and cover this loach needs.
  • A mature high-flow aquarium with oxygen-rich water and established grazing surfaces.

Think carefully if

  • The aquarium is shorter than 60 cm or cannot support the recommended social group.
  • Water is warm, stagnant, or the aquarium lacks mature biofilm-covered stone.

Cow River Loach is a bottom-dwelling loach requiring a 60 cm or longer aquarium, suitable substrate, stable water, and species-appropriate social housing.

Appearance and Identification

A small, broad-headed hillstream loach with a flattened underside, mottled earthy colours, and wide gripping fins.

Rare in the aquarium trade; identification should remain tied to collection locality when available.

Mature males may have a squarer head, stronger pectoral-fin rays, or breeding tubercles, while females are usually fuller through the abdomen. These differences are subtle and species identification should come first.

Tank Requirements

Suggested filter
About 240–300 litres an hour
Suggested heater
About 50–100 W for this tank
Minimum tank volume
60 litres
Minimum tank length
60 cm
Minimum group size
3
Recommended group size
5
Activity level
Moderate
Flow preference
High
Planting preference
Lightly planted
Hiding places
Yes
Lid recommended
Yes
Jumping risk
Medium

Use a mature aquarium at least 60 cm long with high dissolved oxygen, strong but varied current, and smooth stones exposed to bright enough light for biofilm growth. Provide quieter pockets behind rock and wood, keep nitrate and organic waste low, and use a tight cover.

Behaviour and Tankmates

Cow River Loach spends most of its time attached to stone, glass, or wood while grazing and moving between current-facing positions. Males may posture or chase over favoured rocks, but serious injury is uncommon when the footprint contains several feeding territories.

Keep at least 3, preferably 5 or more, where space allows. Multiple grazing zones and broken sight lines reduce competition.

Adults may defend prime feeding stones for short periods. Spread hardscape and food across the footprint.

Choose small to medium peaceful fish that enjoy clean, oxygen-rich water. Avoid warm, stagnant setups, aggressive bottom dwellers, and fish that monopolise all grazing surfaces.

Check tankmates for this species

Water Parameters

Temperature
20–25 °C
pH
6–7.5
GH
1–10
KH
0–6
TDS
30–180
Stability importance
Important

Prioritise high dissolved oxygen, cool-to-moderate temperature, strong surface movement, and very low organic waste. Heat reduces the oxygen safety margin.

Parameter caveat
Do not place a newly imported rheophilic loach directly into a warm, low-flow aquarium. Acclimate gradually and confirm that the fish can reach quiet resting pockets as well as current.

Feeding

Diet types
Algae Grazer, Aufwuchs Grazer, Omnivore
Feeding frequency
Daily
Preferred foods
  • Biofilm and natural aufwuchsMaintain mature stone and wood surfaces so the fish can graze throughout the day.
  • Quality algae or aufwuchs wafersUse a sinking food containing plant material and some animal protein.
  • Small frozen invertebratesOffer occasional Artemia, Daphnia, cyclops, or finely chopped insect larvae.

A grazer of biofilm and algae on rocks. Supplement with algae wafers and small sinking foods.

Distribute food across several stones so dominant fish cannot guard one feeding point. Do not rely on algae growth alone.

Breeding

Breeding type
Egg Layer, Egg Scatterer
Breeding difficulty
Difficult
Breeding temperature
22.5 °C
Breeding pH
6.8
Brood or egg count
Usually described as a modest scatter of small eggs; dependable species-specific counts are limited.
Incubation
4 days
Parental care
None
Baby foods
  • Infusoria or cultured microscopic foodUse when newly free-swimming fry are too small for Artemia.
  • MicrowormsIntroduce once fry actively search the bottom.
  • Newly hatched Artemia naupliiUse after fry are large enough to swallow nauplii.

Captive breeding is uncommon but may occur in a mature stream aquarium. Condition adults with abundant natural grazing and small live foods, provide gravel, rock crevices, and quieter pockets, and avoid disturbing any eggs or newly emerged fry. Parental care is not expected.

Habitat and Origin

Geographic origin
Asia, Indonesia, Malaysia, Southeast Asia
Natural habitat
Clearwater, Fast Stream, Fast-Flowing Stream, Rocky Shoreline
Aquarium contexts
Freshwater Aquarium, High-Flow Aquarium, Species-Only Aquarium
Audience level
Specialist

Classification

Profile type
Recognized species
Genus
Neogastromyzon
Family
Gastromyzontidae
Species group
Fish, Loaches

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Crimson Loach

Schistura sp. Crimson

Care level
Specialist
Adult size
5.6–8 cm
Minimum tank
80 litres
Temperature
20–26 °C

Deze Chinese Sucker

Sinogastromyzon dezeensis

Care level
Specialist
Adult size
7–10 cm
Minimum tank
100 litres
Temperature
18–25 °C

Dwarf Chain Loach

Ambastaia sidthimunki

Care level
Intermediate
Adult size
4.2–6 cm
Minimum tank
100 litres
Temperature
24–28 °C

Emperor Loach

Botia udomritthiruji

Care level
Advanced
Adult size
10.5–15 cm
Minimum tank
180 litres
Temperature
23–28 °C

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