Acheilognathus rhombeus

Family: Cyprinidae

Acheilognathus rhombeus — a Cyprinidae from Japan, peaceful; males spar gently in breeding dress. Reaches 10.1–14.9 cm; sociable; a larger group spreads any squabbles. 15–25 °C.

Care parameters

Water temperature: 15–25 °C
pH: 6.5–7.5
GH hardness: 5–15 dGH
Adult length: 10.1–14.9 cm
Minimum tank: 266 L
Water layer: Bottom-dwelling
Difficulty: Moderate
Temperament: Peaceful; males spar gently in breeding dress
Origin: Japan

Species overview

Acheilognathus rhombeus is a Cyprinidae from Japan. In the wild it prefers clear streams and rivers over gravel; in the aquarium it stays peaceful. Plan on 10.1–14.9 cm of adult fish at 15–25 °C. Related profiles: Acheilognathus barbatulus, Acheilognathus cyanostigma, Acheilognathus gracilis.

Native biotope

Habitat: Clear streams and rivers over gravel
Flow: Moderate, well-oxygenated current
Dissolved O₂: Appreciates well-oxygenated water

Aquascape & hardware

Substrate: Fine gravel and sand
Hardscape: Water-worn stones and driftwood
Plants: Hardy rooted plants along the margins

Temperament, diet & tankmates

Schooling: Sociable; a larger group spreads any squabbles
Diet: Omnivore with a taste for vegetable foods and small live fare
Recommended tankmates: White-cloud mountain minnows — Share its calm, cool temperament
Avoid keeping with: Large or boisterous fish — Outcompeted at feeding time

Breeding & notes

Sexual dimorphism: Males often slimmer and more colourful
Breeding method: Spawns inside living freshwater mussels; no parental care

Frequently asked questions

Is Acheilognathus rhombeus easy to keep?

A moderate-level species: peaceful; males spar gently in breeding dress; stable water matters more than fancy equipment.

What temperature and water chemistry does Acheilognathus rhombeus need?

Set the heater to 15–25 °C and avoid swings. pH 6.5–7.5, GH 5–15 dGH suit it.

How big does Acheilognathus rhombeus get, and what tank size?

Full size is 10.1–14.9 cm. Minimum tank: 266 L, with open swimming space along its bottom-dwelling habits.

What does Acheilognathus rhombeus eat?

Omnivore with a taste for vegetable foods and small live fare. Vary the menu — quality flakes or pellets plus frozen or live foods.

Can Acheilognathus rhombeus live with other fish?

Peaceful; males spar gently in breeding dress; sociable; a larger group spreads any squabbles. Good company: White-cloud mountain minnows — Share its calm, cool temperament. Keep away from Large or boisterous fish — Outcompeted at feeding time.

Where does Acheilognathus rhombeus come from?

Native to Japan, where it lives in clear streams and rivers over gravel. Moderate, well-oxygenated current; Appreciates well-oxygenated water.

Does Acheilognathus rhombeus jump?

Jumping is not a known issue; cover the tank anyway during water changes.

How does Acheilognathus rhombeus breed?

Spawns inside living freshwater mussels; no parental care. Males often slimmer and more colourful.