Identification:
Morphological Characteristics:
Medium-sized mussels with thick, ear-shaped shells. The inner surface is shallow, with a deep indentation near the hinge region. The anterior edge is rounded, the ventral edge curves evenly, and the posterior edge forms a rounded angle in the lower half. The outer shell surface is black and covered with numerous protrusions. These protrusions, along with wrinkles on the dorsal posterior region of the shell, form a “character” pattern that runs from the anterior to the posterior end of the shell. The nacre (mother-of-pearl) is yellow or pinkish-white.
Biology and Ecology:
Lives in rivers of mountainous and midland regions, with soft mud-sand substrates.
Distribution:
In Vietnam: Rivers in the mountainous and midland regions of the Northeast and the Red River Delta, as well as in Nghe An and Ha Tinh provinces.
Worldwide: China (Yangtze River, Hubei, Hunan).
Value:
Of value for research on river and lake ecosystems. The thick shell is used for making buttons and mother-of-pearl inlays.
Conservation Status:
Currently heavily exploited. Prior to 1975, it was commonly found in rivers of the Red River Delta. After 1975, especially from 1990 to the present, due to the strong development of handicrafts using mussel shells, the annual exploitation volume increased significantly, leading to a noticeable decrease in numbers, potentially up to 20%. The distribution area of this species, Trai cóc hình tai, before 1975 extended throughout the Red River Delta, stretching to Nghe An and Ha Tinh provinces, covering over 20,000 km². Currently, due to intense exploitation and pollution of rivers in the delta and midland areas, the distribution area has shrunk to approximately 5,000 km².
IUCN Red List Category:
VU B2a,b,e + 3d (Vulnerable)
Conservation Measures:
Included in the Vietnam Red Data Book and the list of species to be protected by the fisheries sector since before 1996. Recommendations: Limit exploitation and protect against river water pollution. Conduct further research to increase population numbers through artificial breeding.