Tonkin Rainbow Bitterling (Acheilognathus tonkinensis)

Common Name

Vietnam Bitterling
Acheilognathus tonkinensis

This is the Vietnam Bitterling, sometimes also called the Tonkin Bitterling, a compact, deep-bodied cyprinid known for males that light up in breeding condition and a spawning method that involves freshwater mussels. If you enjoy fish with a little drama and a very weird family plan, bitterlings deliver.

Origin and Habitat

Acheilognathus tonkinensis is recorded from northern Viet Nam and southern China, centered on the Red River drainage, and it is also reported from the Nam Mat basin in Laos.

Bitterlings as a group are typically associated with lowland freshwater habitats such as slower river margins, ponds, lakes, and irrigation ditches where aquatic plants and fine substrates are common. What matters most for breeding is the presence of living freshwater mussels, because the eggs are placed into mussels and develop there.

Biotope: A Red River drainage inspired setup can be built around gentle flow, sandy or silty bottoms, and patches of submerged plants with open lanes for schooling.

Compatible species (biotope examples):

• Rhodeus ocellatus
• Hemiculter leucisculus
• Opsariichthys minutus
• Discogobio microstoma

Suggested plants:

• Vallisneria spiralis
• Hydrilla verticillata
• Najas indica
• Ceratophyllum demersum

Temperature and Water Conditions

A stable, seasonally flexible range works well. We recommend 21 to 25 °C (70 to 77 °F) for general care, with a gentle warm up toward the upper end during conditioning.

We do not recommend chasing or altering water parameters except in special breeding situations. Stable conditions are far more important.

• Keep ammonia and nitrite at 0
• Keep nitrate low
• Maintain steady temperature
• Provide clean, well-oxygenated water

Appearance and Size

Males are the showstoppers, especially in breeding condition, when they develop strong iridescence and multi-color highlights. Females are more subtle but display a visible ovipositor during spawning.

Maximum length is about 12.2 cm (4.8 inches), though most aquarium specimens reach 8–10 cm (3.1–3.9 inches).

Diet in the Wild

Bitterlings are opportunistic omnivores and feed on:

• Small invertebrates
• Insect larvae
• Suspended foods
• Biofilm and algae

Feeding in Captivity

Feed to promote color and conditioning without overfeeding. Two small meals daily is ideal.

• Quality micro pellet (staple)
• Spirulina flake (several times weekly)
• Frozen daphnia, cyclops, or baby brine shrimp (2–4x weekly)
• Bloodworms (occasional treat)

Feed only what is consumed within 1–2 minutes.

Behavior and Tank Setup

Vietnam Bitterlings are peaceful, social fish best kept in groups.

• Minimum group: 6 fish
• Keep more females than males if possible

Tank size:

• Minimum: 20 gallons (76 L)
• Recommended: 30 gallons (114 L)
• Breeding setups: 30+ gallons strongly preferred

Setup tips:

• Sand or fine gravel substrate
• Plants along edges
• Open swimming space
• Moderate filtration and oxygenation
• Gentle to moderate flow
• Use a lid

Tank mates:

• Peaceful, non-aggressive fish
• Avoid fin nippers
• Avoid fry predators
• Shrimp may survive, but shrimplets are at risk

Breeding

This species is a mussel spawner. Females use an ovipositor to deposit eggs inside live freshwater mussels, where the fry develop.

Breeding with Mussels

• Use healthy, legal, captive-raised freshwater mussels
• Provide 2–4 mussels per 20–30 gallon tank
• Ensure mussels open regularly and behave normally
• Maintain gentle flow and high oxygen
• Prevent waste buildup

Important:

• Stressed mussels may eject eggs
• Add more mussels if breeding fails
• Try different compatible species if needed
• Avoid copper and most medications

Spawning triggers:

• Stable conditions
• High-quality feeding
• Low-stress environment

Breeder’s Tips

• Gradually raise temperature into mid-20s °C
• Increase feeding with frozen foods
• Provide multiple mussels
• Add dense plant cover for fry
• Start fry on infusoria and powdered foods
• Transition to baby brine shrimp
• Perform small, frequent water changes
• Keep conditions stable

Quick Facts

• Scientific Name: Acheilognathus tonkinensis
• Common Name: Vietnam Bitterling
• Origin: Vietnam, China, Laos
• Size: Up to 4.8 inches (12.2 cm)
• Temperature: 70–77 °F (21–25 °C)
• Temperament: Peaceful, social
• Diet: Omnivore
• Breeding: Mussel spawner

Tropical Fish Co. Notes

If you love fish with personality, this is a standout species. Males develop striking coloration, and their breeding behavior is one of the most fascinating in freshwater aquariums.