Abstract
The harvest of Manila clam Ruditapes phillipinarum has been drastically declining in Japan. One of the reasons is likely due to the nationwide spread of Perkinsus olseni in the clams. Here, we report that a P. olseni infection has occurred in Manila clams on Shodoshima Island facing severe depletion of its natural resources.
132 Manila clams were collected five times in 2016. The percentage of nested PCR-positive clams was 6.7-92.9 ％ from October 22 to December 8. The findings showed that the prevalence of the Perkinsus protozoan infection was different largely depending on the season. 176 Manila clams were collected six times in 2017. The percentage of nested PCR-positive clams was 3.1-17.2 ％ from May 18 to October 25. Among them, the clams with shell length ≤15 mm were included, and the increasing trend in infection intensity was suggested by differences among band intensities of their PCR products. 30 nested PCR products were randomly chosen for sequencing. The obtained sequences were clustered into two genotypes. The maximum likelihood phylogenetic tree based on the ITS1-5.8S rRNA-ITS2 sequences of eight Perkinsus species showed that both genotypes were located in P. olseni/atlanticus clade, and therefore were identified as P. olseni.
