The population dynamics and sexual strategy of Anodonta woodiana (Bivalvia: Unionacea) in Plover Cove Reservoir, Hong Kong

A 12-month investigation of the population dynamics, growth, ageing, reproduction and sexuality of Anodonta woodiana (Lea, 1834) in Plover Cove Reservoir, Hong Kong, has been undertaken. Recruitment occurs in the summer, May through July being the period of peak incidence of glochidia on captive fish hosts. Juveniles grow rapidly to a shell length of 30 mm and are sexually mature by the following spring. A study of the population structure of A. woodiana indicated that most animals were less than 8 years old. Results of a Walford plot for this species indicated a maximum theoretical shell length (in Plover Cove) of 162·5 mm and a life span of approximately 12 years; the latter is in good agreement with age estimates for European unionids.
Anodonta woodiana is dioecious with females predominating in a ratio of 60:40. A very small number of individuals (0·3%) are hermaphrodite. Males possess mature gonads throughout the year whereas females come into reproductive condition during the spring. There was no evidence of shell form sexual dimorphism, as has been recorded for other unionaceans.
The reproductive strategy and time of gonad maturation of A. woodiana is compared with that of unionids from elsewhere and with other fresh water bivalves from southern China.