First report of Perkinsus honshuensis in the variegated carpet shell clam Ruditapes variegatus in Korea

Abstract

The recent discovery of Perkinsus honshuensis, a new Perkinsus species infecting Manila clams Ruditapes philippinarum (Sowerby, 1852), in Japan, suggested that, based on proximity, P. honshuensis could also be in Korean waters, where to date, P. olseni was believed to be the only Perkinsus species present. Perkinsus sp. infections consistently occurred among Ruditapes variegatus clams on a pebble beach on Jeju Island, off the south coast of Korea. The typical 'signet ring' morphology of the parasite was observed in the connective tissue of the digestive gland, and infection intensity was comparatively low (3.3 × 10 3 ± 1.2 × 10 4 to 1.3 × 10 4 ± 6.1 × 10 4 cells g −1 gill weight). Further DNA analyses of internal transcribed spacer (ITS-1, 5.8S and ITS-2) and non-transcribed spacer (NTS) regions of the parasite showed 98.9−99.8 and 98.5−99.5% similarity to those of P. honshuensis from Japan, respectively. Phylogenetic analyses using ITS and NTS sequences indicated that Perkinsus sp. from Jeju formed a highly supported clade with P. honshuensis. This is the first report of P. honshuensis infections in clams in Korean waters and the first report of R. variegatus as a host for that parasite.

Scanning electron microscopic observation of the in vitro cultured protozoan, Perkinsus olseni, isolated from the Manila clam, Ruditapes philippinarum

“…Since the first occurrence of P. olseni in Manila clams in Asia, described in the late 1990s by molecular studies [2,11,12], other parasites, such as P. honshuensis were associated with Manila clams. Of note, this new parasite species has been described in Manila clams from Japan and in R. variegatus collected on Jeju Island, on the southern coast of Korea, after a nation-wide survey of P. honshuensis: P. honshuensis specific primers were used to screen clams from 23 different locations [13][14][15]. Thus, the distribution of P. honshuensis appears to be restricted to Jeju Island (with respect to Korea) at the present.…”