Identification
Morphological Characteristics:
Large size, thin shell, elongated ellipse shape. Length can reach 23-25 cm. The shell’s umbo is low, making the shell flat. The anterior margin is rounded, the ventral margin is straight, slightly concave in the middle, and the posterior margin is nearly round. The outer shell surface is smooth. In young individuals, the shell is yellowish-green with numerous green radial lines. In older individuals, the shell is yellow-green with coarse growth lines. Concentric dark brown bands are present. The nacre is white, slightly pink, and iridescent.
Biology and Ecology
Reproduction:
Reproduces at the beginning of summer. This species is commonly found in the muddy-sandy bottoms of rivers, lakes, and ponds in the plains and midlands of northern Vietnam. It adapts to the summer and winter weather conditions.
Distribution
Within Vietnam:
Plains and midlands of Northern Vietnam.
Worldwide:
China (South China).
Value
Ecological Significance:
Valuable for research on freshwater river and lake ecosystems.
Status
Historical Population:
Before 1975, this species was commonly found in rivers of the Northern plains, with a density of approximately 2-3 individuals per square meter of the bottom substrate. Annually, in the summer, the local people in Quảng Bá Lake and Tây Lake (Hanoi) harvested hundreds of kilograms.
Current Population:
After 1975, especially from 1990 to the present, the annual exploitation has increased, leading to a significant decrease in the population, possibly up to 20%. Population numbers fluctuate significantly each year, depending on exploitation rates.
Distribution Area:
The distribution area was approximately 15,000 km² before 1975. Currently, with many lakes and ponds being filled, and due to pollution in rivers and lakes, the distribution area has decreased significantly, estimated to be only about 2,000 km².
IUCN Status:
VU B2a,b,e+3a,d (Vulnerable)
Conservation Measures
Current Protections and Recommendations:
It has been included in the Vietnam Red Book and the list of protected species of the Fisheries sector since before 1996. Recommendations: Reduce exploitation intensity, harvest during the non-reproductive season, rotate harvesting locations, and combat water pollution in key habitats of the species.