Longitudinal distribution and body size of Macrobrachium nipponense, M. formosense and M. japonicum in the Shimanto River

Abstract

 This study aimed to examine the distributions and body sizes of the freshwater amphidromous prawns Macrobrachium nipponense, M. formosense and M. japonicum in the Shimanto River, Kochi Prefecture, Japan. The upstream distribution limits of M. nipponense, M. formosense and M. japonicum were 28 km, 54 km and 83 km from the river mouth, respectively. Recruitment was initiated in August or September; the newly recruited groups of three species exhibited a mode of approximately 7 mm in the carapace length distribution by December. The subsequent mode significantly increased to approximately 13 mm in April or May, immediately before the breeding season; simultaneously, the percentage of large individuals judged to be older than the newly recruited groups was lower in M. nipponense and M. formosense than in M. japonicum.