What the Amur Bitterling Is and Where It Lives

The Amur bitterling is a small freshwater fish native to eastern Asia, particularly the Amur River basin that borders Russia and China. Adults rarely exceed 2 inches in length, making them one of the smallest fish you can keep in a home aquarium. They have a compressed, elongated body with a silvery-green coloration that intensifies during breeding season, when males develop red and blue markings along their sides and fins.

In the wild, Amur bitterlings inhabit slow-moving rivers, streams, and floodplain lakes with dense aquatic vegetation. They prefer cool to moderate water temperatures and areas with plenty of plants and organic matter on the bottom. Their native range has contracted over recent decades due to habitat loss and water pollution, but they remain relatively common in parts of their original distribution.

Key Takeaways

  • Amur bitterlings are tiny fish that breed inside freshwater mussels, a behavior that makes them unusual among aquarium fish and requires specific tank conditions to observe.
  • They thrive in cool water between 60 and 72 degrees Fahrenheit and need densely planted tanks with soft substrate where mussels can burrow.
  • In home aquariums, they are peaceful community fish that do well with other small, non-aggressive species but should not be housed with fish large enough to eat them.
  • Feeding is straightforward—they accept small live foods like daphnia and bloodworms, as well as high-quality micro pellets designed for small fish.
  • Breeding in captivity is possible but challenging; it requires live freshwater mussels, stable water conditions, and patience to observe the entire cycle.

Tank Setup and Water Conditions

Amur bitterlings do best in tanks of at least 20 gallons, though smaller groups can manage in 10-gallon setups if water quality is maintained carefully. The water should be cool—ideally between 60 and 72 degrees Fahrenheit—which means they are not suited to tropical tanks kept at 76 degrees or higher. If your room temperature naturally stays in this range, you may not need a heater at all; in warmer climates, a chiller or placement away from direct sunlight helps keep the tank cool.

Substrate should be soft sand or fine gravel at least 2 inches deep, because bitterlings spend time foraging on the bottom and mussels need to burrow. Dense aquatic plants are essential—Java moss, Anubias, and stem plants all work well. These plants provide shelter, reduce stress, and create the low-light environment bitterlings prefer. Water should be slightly acidic to neutral (pH 6.0 to 7.0) with moderate hardness. Weekly water changes of 25 to 30 percent keep nitrate levels low and maintain the cool, clean conditions they need.

Feeding and Diet

Amur bitterlings are micropredators in the wild, feeding on small invertebrates, insect larvae, and zooplankton. In captivity, they thrive on a varied diet of small live foods: daphnia, copepods, and bloodworms are all excellent choices. Live food is preferable because it triggers their natural hunting behavior and ensures they receive the nutrition they need to stay healthy and develop proper coloration.

High-quality micro pellets designed for small fish can supplement live food, though they should not be the only diet. Feed small amounts once or twice daily—only what the fish can consume in a few minutes. Overfeeding fouls the tank quickly in small setups and leads to poor water quality. Bitterlings have small mouths and modest appetites, so restraint is important. Occasional treats of blanched vegetables like zucchini are accepted but not necessary if they receive varied live foods.

Behavior and Tank Mates

Amur bitterlings are peaceful and social fish that do well in groups of four or more. They are not aggressive toward other fish, though males may display mildly territorial behavior during breeding season. They spend much of their time near the bottom and in plants, foraging and resting rather than actively swimming in open water.

Good tank mates include other small, peaceful fish such as small rasboras, dwarf corydoras catfish, and other bitterling species. Avoid housing them with large fish, aggressive species, or anything that might view them as food—a 3-inch fish can easily swallow a 2-inch bitterling. They also should not be kept with fish that prefer warm water, since the cool temperature bitterlings need would stress tropical species. Shrimp and snails are compatible and actually beneficial, as they help clean the tank and do not compete for food.

Breeding Behavior and Mussel Dependency

The Amur bitterling has one of the most remarkable breeding strategies in freshwater fish: females lay eggs inside living freshwater mussels. During breeding season, the female develops a long ovipositor—a tube-like extension from her body—which she uses to insert eggs into the mussel's gill chamber. The male fertilizes the eggs by releasing sperm near the mussel's intake siphon. The mussel's tissues protect the developing eggs, and the fry remain inside until they are large enough to leave.

To observe or breed bitterlings in captivity, you must have live freshwater mussels in the tank. Species like Unio or Anodonta mussels work, though availability varies by region. The mussels must be healthy and large enough to accept eggs—typically at least 2 to 3 inches long. Without mussels, breeding cannot occur, and the fish will not spawn. Even with mussels present, breeding requires stable water conditions, proper temperature, good nutrition, and often several months of patience. The fry emerge over several weeks and are extremely small, requiring infusoria or liquid fry food for the first few days.

Health and Common Issues

Amur bitterlings are hardy fish when kept in appropriate conditions, but they are sensitive to warm water and poor water quality. The most common problem is temperature stress—keeping them too warm leads to lethargy, loss of color, and shortened lifespan. Maintain the cool range they need, and most health issues will not arise.

Ich (white spot disease) and other parasites can occur if water quality drops or if new fish are not quarantined. Regular water changes, stable conditions, and observation for signs of illness—white spots, torn fins, unusual behavior—help prevent problems. If illness occurs, treat the entire tank rather than isolating the fish, since bitterlings are small and handling them causes stress. A slight temperature increase (to 70 degrees if they are not already at that level) combined with salt treatment or medication designed for small fish usually resolves parasitic infections.

Sourcing and Legal Considerations

Amur bitterlings are available from specialty aquarium retailers and online fish suppliers, though they are less common than tropical species. Prices vary but are typically modest—usually between five and fifteen dollars per fish. Availability depends on your region; they are more readily found in areas with active aquarium clubs or retailers specializing in temperate and Asian fish.

Check local regulations before purchasing, as some regions restrict or prohibit the import of non-native species. In most of North America and Europe, they are legal to keep, but rules vary by state and country. If you decide to keep them, never release them into local waterways—even well-intentioned releases can harm native ecosystems. Keep them only in closed aquarium systems.

Frequently Asked Questions

Can Amur bitterlings live in an unheated tank?

Yes, if your room temperature stays between 60 and 72 degrees Fahrenheit year-round. In most homes, this means a basement or cool room away from heating vents and direct sunlight. If your home is warmer, you will need a chiller or must accept that the fish will be stressed and have a shorter lifespan.

Do I need mussels to keep Amur bitterlings?

No—they live and thrive without mussels. Mussels are only necessary if you want to breed them. Many aquarists keep bitterlings for years without attempting to breed them, and the fish remain healthy and colorful in a well-maintained tank.

How many Amur bitterlings can I keep in a 20-gallon tank?

A group of six to eight fish is reasonable for a 20-gallon tank with good filtration and weekly water changes. They are small and do not produce much waste individually, but they are social and do better in groups. Avoid overcrowding, as it stresses the fish and degrades water quality quickly.

What size do Amur bitterlings grow to?

Most adults reach 1.5 to 2 inches in length. Occasionally, a fish may reach 2.5 inches, but this is uncommon. Their small size is part of their appeal for planted tanks and small aquariums.

Can I keep Amur bitterlings with goldfish?

No. Goldfish prefer cool water but are much larger and will eat bitterlings. Goldfish also produce heavy waste and need larger tanks. They are incompatible tank mates in every practical way.