Abstract
Corbicula japonica is the best-known bivalve inhabiting widely in brackish estuaries and lakes in Japan. Although this species has been most commercially important species of inland fisheries in Japan, the gradual decline in its production over 40 years caused not only economic problems in fishery industry but also ecological disturbances in biodiversity conservation. The aim of this study was to evaluate the reproduction structure of C. japonica populations in major fishing brackish lakes based on the genetic diversity inferred by mitochondrial DNA sequence analysis of the cytochrome oxidase c subunit I gene. Of a total of 188 C. japonica individuals collected in Lakes Shinji, Jusan, Ogawara and Abashiri, 25 haplotypes were obtained, and only the haplotype HT01 was apparent with relatively high abundance in all lakes. Minimum spanning network analysis of haplotypes showed different population structures between Lake Shinji and Lakes Jusan, Ogawara and Abashiri. In addition, pairwise population genetic distance FST and ΦST values were significantly higher in Lake Shinji than Lakes Jusan, Ogawara and Abashiri. The mismatch distribution analysis showed unimodal profile for Lakes Jusan and Ogawara and bimodal profile for Lakes Shinji and Abashiri. Those results indicate a recent population expansion in all lakes, and Lakes Shinji and Abashiri and Lakes Jusan and Ogawara maintained continuous reproduction structure and suffered to rapid population growth, respectively.
Highlights
Species belonging to the genus Corbicula attain an almost worldwide distribution and inhabit in estuaries, lakes, and rivers [1]-[3]
The average shell length and shell height of C. japonica individuals collected in Lakes Jusan, Ogawara and Abashiri ranged from 22.34 ± 1.43 mm to 26.73 ± 2.51 mm and from 20.42 ± 1.31 mm to 23.90 ± 2.24 mm, respectively
The respective values of those collected in Lake Shinji were determined to be 18.16 ± 2.17 mm and 15.87 ± 1.76 mm, and relatively small shell size compared with the other lakes (Table 1)
Summary
Species belonging to the genus Corbicula attain an almost worldwide distribution and inhabit in estuaries, lakes, and rivers [1]-[3]. C. japonica has been one of the most important species for inland fisheries in Japan [9], and occupied 99% of the total catch of Corbicula [8]. The catch of Corbicula from 2002 to 2011 reached average 12,000 tons, which corresponded to approximately 30% of the total catch of inland fisheries [10]. A bulk of anonymous Corbicula individuals was successively imported from eastern Asia [12]. It has been concerned with the genetic disturbance of C. japonica in Japan, but its genetic diversity and reproduction structure are still not well understood
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