Tanakia chii（Paratanakia chii）

The Tanakia chii is a small freshwater fish belonging to the family Cyprinidae and the genus Rhodeus. It is primarily found in East Asia and is notable for its small size, vibrant coloration, and unique reproductive behavior, making it a typical representative of bitterlings. Below is a detailed introduction to Tanakia chii:

Physical Characteristics

• Size: Small-sized, with adults typically measuring 4–6 cm in length.
• Coloration: The body is silvery-white or pale gray, with fins displaying a mix of red, yellow, orange, and white. During the breeding season, males exhibit more vivid colors, including bluish-green iridescence, gray-black reflections, and bright orange-red bellies.
• Fins: The fins are usually transparent or slightly yellowish, with males’ fins sometimes showcasing orange-red or purplish-red decorations during breeding periods.

Habitat

• Distribution: Mainly found in freshwater habitats in China, including rivers, lakes, and ponds, particularly in areas with slow-moving water and abundant vegetation.
• Living Environment: Prefers shallow waters rich in aquatic plants. The substrate is often sandy or muddy, providing excellent cover and feeding grounds.

Behavior

• Diet: Omnivorous, feeding on plankton, aquatic insect larvae, algae, and organic debris.
• Social Nature: Peaceful and usually forms groups, making it suitable for community aquariums with similarly sized, non-aggressive species.

Reproductive Traits

The most fascinating aspect of Tanakia chii lies in its unique host-reliant reproductive behavior:

1. Host Selection: During the breeding season, females seek suitable freshwater mussels as egg-laying hosts.
2. Egg-Laying Process: Females use an elongated ovipositor to deposit eggs into the gill chambers of the mussel, while males release sperm nearby to fertilize the eggs.
3. Egg Protection: The eggs develop within the mussel, where they are shielded from external threats.
4. Hatching: Once fully developed, the fry emerge from the mussel and begin their independent lives.

Aquarium Care

Tanakia chii is a popular ornamental fish, but its breeding requires specific environmental conditions, particularly the presence of freshwater mussels as hosts.

1. Tank Requirements:

   • Size: A tank of 10 gallons or larger is recommended.
   • Temperature: 15–30°C (59–86°F).
   • Water Quality: pH 6.5–7.5, clear and well-oxygenated water.
   • Setup: Use fine sand or muddy substrate with aquatic plants to provide hiding spots and feeding areas.

2. Diet: Can be fed small pellet foods, frozen bloodworms, brine shrimp, and algae supplements.

3. Breeding Environment: Successful reproduction in aquariums requires the addition of freshwater mussels as hosts; otherwise, breeding may not occur.

Conservation Status

Although Tanakia chii is not currently listed as an endangered species, its natural habitats, such as rivers and lakes, face threats from pollution and human activities. Protecting these habitats and researching artificial breeding techniques are crucial for maintaining the population health of this species.