How big does Harlequin Rasbora get?

Harlequin Rasbora reaches an adult standard length of 3–4.5 cm (excluding the caudal fin). Size the tank for that, not for the juvenile you bring home — the difference is often several times over, and upgrading later costs more than buying once.

What water does Harlequin Rasbora need?

22–28 °C, pH 6–7.5, 2–12 dGH, 1–6 dKH. At 6 °C wide it is one of the more forgiving ranges.

What is the smallest tank for Harlequin Rasbora?

At least 40 L, and no shorter than 50 cm. That is the floor for long-term keeping, not for short-term survival: volume buys water stability and length buys swimming room, and neither substitutes for the other. It is a schooling fish: keep at least 8 together. Fewer than that and it hides, loses colour, and aggression has nowhere to spread.

What is Harlequin Rasbora like to keep?

Temperament: peaceful. Difficulty: beginner. It occupies the middle and is omnivore. With plants it is "Leaves plants alone".

G-01 / 13Freshwater

Harlequin Rasbora三角灯

Trigonostigma heteromorpha · Cyprinidae

A small cyprinid with a black wedge, and one of the few that thrives in neutral tap water.

Illustration to come

G-01 / 13 · Harlequin Rasbora Trigonostigma heteromorpha

SpecificationsFish atlas

Name: 三角灯
Scientific name: Trigonostigma heteromorpha
Family: Cyprinidae
Origin: Southeast Asia (southern Thailand, Malay Peninsula, Sumatra)
Adult size: 3–4.5 cm
Temperament: Peaceful
Diet: Omnivore
Water level: Middle
Level: Beginner
School size: ≥ 8
Min. tank: 40 L
Min. length: 50 cm
Plant safe: Leaves plants alone

Water requirementsFreshwater

Temp.22–28 °C

pH6–7.5

Hardness2–12 dGH

Alkalinity1–6 dKH

Units: temperature in °C, hardness in German degrees (dGH / dKH), marine salinity as specific gravity at 25 °C, volume in litres. These are the values recorded for the species and do not follow the site unit switcher.

Keeping notes

1A forgiving blackwater fish that lives long even in neutral tap water.
2In groups of eight or more the triangular blotch shifts in intensity with mood.
3Prefers gentle current and dense planting; slightly acidic water deepens the red.

Frequently asked questions

How big does Harlequin Rasbora get?: Harlequin Rasbora reaches an adult standard length of 3–4.5 cm (excluding the caudal fin). Size the tank for that, not for the juvenile you bring home — the difference is often several times over, and upgrading later costs more than buying once.
What water does Harlequin Rasbora need?: 22–28 °C, pH 6–7.5, 2–12 dGH, 1–6 dKH. At 6 °C wide it is one of the more forgiving ranges.
What is the smallest tank for Harlequin Rasbora?: At least 40 L, and no shorter than 50 cm. That is the floor for long-term keeping, not for short-term survival: volume buys water stability and length buys swimming room, and neither substitutes for the other. It is a schooling fish: keep at least 8 together. Fewer than that and it hides, loses colour, and aggression has nowhere to spread.
What is Harlequin Rasbora like to keep?: Temperament: peaceful. Difficulty: beginner. It occupies the middle and is omnivore. With plants it is "Leaves plants alone".