Rainbow shark - Epalzeorhynchos frenatum

Scientific name: Epalzeorhynchos frenatum

Common name: Rainbow shark

Family: Cyprinidae

Usual size in fish tanks: 12 - 15 cm (4.72 - 5.91 inch)

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Recommended pH range: 6 - 7.5

Recommended water hardness: 5 - 12°N (89.29 - 214.29ppm)

0°C 32°F30°C 86°F

Recommended temperature range: 24 - 27 °C (75.2 - 80.6°F)

The way how these fish reproduce: Spawning

Where the species comes from: Southeast Asia

Temperament to its own species: aggressive/territorial

Temperament toward other fish species: aggressive to smaller

Usual place in the tank: Bottom levels

General Information

Rainbow shark (Epalzeorhynchos frenatum; syn. Labeo frenatus) is a semi-aggressive labeonine cyprinid native to Southeast Asia—notably the Mekong, Chao Phraya, Mae Klong (Maeklong) and Xe Bangfai basins. In nature it forages near the bottom over sandy stretches and hard surfaces, moving onto seasonally flooded plains during high water. Typical aquarium size is 12–15 cm (up to ~15 cm TL). Often sold as the “red-finned/rainbow shark”; do not confuse with the red-tailed black shark (E. bicolor).

Food & Feeding

Omnivore with a strong aufwuchs/algae-grazing component. Provide sinking algae wafers and veg-rich pellets as the staple; rotate frozen/live items (daphnia, brine shrimp, mysis, finely chopped prawn) a few times weekly. Offer blanched vegetables (spinach, peas, zucchini) to meet fiber needs. Feed small portions 1–2× daily to keep organics down.

Sexing

Sexual dimorphism is subtle. Mature females are deeper-bodied/plumper; males tend to be slimmer and can show darker edging in the caudal/anal fins. Reliable sexing usually requires comparison in a group.

Breeding

Egg-scatterer in the wild. Home aquarium spawnings are not reliably documented; commercial production is typically via large outdoor ponds or hormonal induction. Treat this species as display-only for hobbyists.

Lifespan

Commonly 6–10 years with space, strong filtration and low nitrate; 8 years is achievable in well-kept systems.

Tank Requirements & Water Parameters

Footprint & cover: long tank, min. 120 cm/4′ (bigger for adults). Use fine sand to protect barbels, plus rounded stones/wood, sturdy plants and multiple caves to break line-of-sight.
Flow & oxygen: moderate–strong current, high O₂; emulate clear running rivers.
Water: pH ~6.0–7.5, hardness ~5–12 °dH, temperature 24–27 °C (tolerates ~23–29 °C). Keep nitrate low and parameters stable.
Maintenance: robust filtration, tight lid (strong jumper), regular large water changes.

Compatibility & Temperament

Territorial, especially to look-alikes and bottom dwellers. Best kept singly in most aquaria; groups require very large, structured tanks and still carry risk of serious aggression. Choose robust, fast mid-water companions; avoid small, slow or long-finned species.

Behaviour & Usual Place in the Tank

Primarily a bottom to lower-mid water forager that patrols surfaces and defends a territory, especially as it matures. Provide open lanes for cruising and shaded retreats to reduce skirmishes.

Short Description

Rainbow sharks are striking, red-finned river cyprinids from mainland Southeast Asia. They need a long, well-filtered tank with sand, current and many hides. Feed veg-rich sinking foods with protein treats. Keep one per tank unless you can house a carefully managed group in a very large, structured setup.

Q&A

Where is it from? Mekong, Chao Phraya, Mae Klong (Maeklong) & Xe Bangfai basins in mainland Southeast Asia.
Peaceful with its own kind? No—strongly territorial; keep singly in typical community tanks.
Algae eater only? No. It grazes algae/periphyton but thrives on a mixed omnivorous diet with plant matter and small invertebrates.