Identification:
Medium-sized mussel with a nearly round shell, the interior deeply concave towards the hinge area. The shell is thick, with a prominent umbo (the oldest part of the shell). The anterior margin is straight, the ventral margin evenly curved, the posterior margin nearly round, and the dorsal margin highly arched. The outer shell surface has many small, round, smooth bumps, evenly distributed across the shell or coalescing into low ridges. The dorsal area has 10-12 oblique ridges. The shell exterior is dark brown; the nacre (inner shell layer) is a glossy white with a bluish iridescence.
Biology, Ecology:
Lives in the surface mud layer of the river bottom in mountainous regions.
Distribution:
- In Vietnam: Cao Bằng Province (Bằng River).
- Globally: China (South China).
Value:
Primarily used as food; the thick shell is used for buttons and mother-of-pearl inlay.
Conservation Status:
A narrow-range species currently subject to significant exploitation. Prior to 1975, it was common in the Bằng River. Since 1990, the annual harvest has increased, resulting in a marked population decline, potentially up to 20%. Surveys conducted from 1999-2001 in the Bằng River (Cao Bằng town area) showed that during the dry season, over a dozen local people were collecting Trai cóc tròn (the local name for this mussel) daily. Each person could collect 1-2 kg in a single day. The mussel’s density is only about 1-3 individuals/m², and its distribution area and habitat have significantly decreased compared to the past.
Red List Category: VU B2a,b,e + 3d.
Conservation Measures:
Included in the Vietnam Red Data Book and the list of species requiring protection by the Fisheries sector since before 1996. Recommendations: Limit the harvesting of Trai cóc tròn, protect and restore the water quality of the Bằng River in the Cao Bằng town area. Restrict sand mining on the Bằng River. Further research into population augmentation through artificial propagation.