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Young-Ghan Cho,Hyun-Sil Kang,Cuong Thanh Le,Mun Gyeong Kwon,Min-Seok Jang,Kwang-Sik Choi 제주대학교 해양과학연구소 2020 해양과환경연구소 연구논문집 Vol.44 No.-
Recently, a putative new hyperparasitic haplosporidian in the genus Urosporidium was identified from metacercariae of the trematode Parvatrema duboisi infecting Manila clam Ruditapes philippinarum on the west coast of Korea. In this study, we applied small subunit ribosomal DNA (SSU rDNA) sequences as a marker to substantiate the phylogenetic relationship of the unidentified Urosporidium within the Order Haplosporida. In our phylogenetic analysis, the 1890 bp of SSU rDNA sequences obtained were closely related to a haplosporidian parasite forming a sister clade to Urosporidium group, although the gene sequences were only 89.22–89.70% similar to Urosporidium spp. Such molecular phylogenetic distance within the genus suggested that the unidentified Urosporidium is a new member of the genus. Accordingly, we report the unidentified haplosporidian hyperparasite as Urosporidium tapetis sp. nov.
이혜미,Young-Ghan Cho,Hee-Do Jeung,Min-Seok Jang,황지연,Kwang-Sik Choi 한국해양과학기술원 2020 Ocean science journal Vol.55 No.4
As a suspension feeder, Manila clam Ruditapes philippinarum (A. Adams and Reeve 1850) plays a crucial role in the coastal soft bottom ecosystem in the temperate region, linking the benthic primary production to the upper trophic level. Manila clam density on tidal flats on the west coast of Korea has been declining for the past decades, and infection by the protozoan parasite Perkinsus olseni (Lester and Davis 1981) is one of the major causes for the decline. Recent studies carried out in Japan revealed that P. olseni induces mortalities of the juveniles in their natural habitats, which may lead to the recruitment failure and subsequent decline in the clam population. In this study, we surveyed P. olseni infection in juvenile Manila clam occurring on two tidal flats on the Taean coast. Ray’s fluid thioglycollate medium assay (RFTM) revealed that P. olseni infection was not limited to the adult clams, and the juvenile and small-sized clams are also infected by P. olseni. As young as four-month-old juveniles from Jugyo tidal flat were infected by P. olseni, with the prevalence (i.e., percentage of the infected individuals) of 75.0% and the intensity of 7.77 × 105 cells g−1 wet tissue weight (WT). The adult Manila clams (SL > 30 mm) from Jugyo tidal flat showed a prevalence of 96.0%, and the intensity as 5.80 × 10 cells g−1 WT. The observed infection prevalence and intensity of the juvenile are somewhat comparable to those of the adult clams, suggesting that a high level of P. olseni infection in the juveniles may lead to mortality and a long term decline in the clam population density.
Jeong-Hwa Kim,Hye-Mi Lee,Young-Ghan Cho,Jong-Seop Shin,Jae-Won You,Kwang-Sik Choi,Hyun-Ki Hong 제주대학교 해양과학연구소 2020 해양과환경연구소 연구논문집 Vol.44 No.-
Marine bivalves are often used as a sentinel species in coastal environmental monitoring since changes in the environmental quality are often well preserved in their cells and tissues. Anadara and Tegillarca species of Arcidae, the blood cockles, are considered to be good sentinel species in monitoring coastal pollution and ecosystem health because they are distributed widely in the subsurface of intertidal mudflats. Internal cellular defense of the blood cockles to physical and biological stresses is mediated by the circulating hemocytes, while their hemocyte types and functions are poorly studied. In this study, we first characterized morphology and immune-related activities of hemocytes of three common blood cockles Anadara broughtonii, A. kagoshimensis, and Tegillarca granosa using flow cytometry. Based on cell morphology and immunological functions, we described five types of hemocytes identically in the three blood cockles: erythrocytes type-I (erythrocytes-I), erythrocytes type-II (erythrocytes-II), granulocytes, hyalinocytes, and blast-like cells. Erythrocytes were round cells containing hemoglobin with numerous granules in the cytoplasm and these cells consist of two central populations. Erythrocytes-I were the most abundant cells accounting for 80–89% of the total circulating hemocytes and exhibited a certain level of lysosome and oxidative capacity. Erythrocytes-II were the largest cells and displayed high lysosome content and the most active oxidative capacity. Both erythrocytes-I and erythrocytes- II did not show phagocytosis capacity. Granulocytes were intermediated-sized hemocytes characterized by granules in the cytoplasm and long pseudopodia on the cell surface, and these cells were mainly engaged in the cellular defense exhibiting the largest lysosome content, the most active phagocytosis, and high oxidative capacity. Contrary to granulocytes, hyalinocytes were comparatively small and round cells and exhibited no granules in the cytoplasm. Hyalinocytes displayed a certain level of lysosome and phagocytosis and oxidative capacities. Blast-like cells characterized by the smallest size and small quantity of cytoplasm and exhibited an absence of phagocytosis and extremely low oxidative capacity, suggesting that this population is not directly involved in the cell-mediated immune activities. In conclusion, flow cytometry indicated that three blood cockles had five types of hemocytes, and the erythrocytes and granulocytes were mainly involved in the immunological activities.
Thatchaneshkanth Subramaniam,Hee‑Jung Lee,Hee‑Do Jeung,Hyun‑Sil Kang,Chul‑Won Kim,Hyung‑Seop Kim,Young‑Ghan Cho,Kwang‑Sik Choi 제주대학교 해양과학연구소 2021 해양과환경연구소 연구논문집 Vol.45 No.-
The Gray mussel Crenomytilus grayanus occurs in high density in the shallow rocky subtidal zone on the east coast of Korea, where the mussel dominates the shallow subtidal benthic community. In this study, we first examined the annual gametogenesis and temporal changes in the tissue composition, which provides crucial information to the management of the mussel on the east coast. Based on histological analysis, oogenesis and spermatogenesis commenced in September, as the small oogonia (16.67 ± 4.87 μm in diameter) and spermatogonia developed on the follicle walls, respectively. In March, the mature oocytes (46.55 ± 9.91 μm in diameter) and spermatozoa dominated the follicle. During May and June, most of the males and females spawned when the surface seawater temperature (SST) increased from 15.5 to 22.3 °C. The total carbohydrate level in the tissue increased dramatically from April to May, which coincided with the chlorophyll-a maximum occurring in April. Condition index, a ratio of tissue weight to shell weight, also increased from February to May and then declined in June, suggesting that most mussels released the gametes through spawning during these months. Our data suggest that C. grayanus is a spring spawner, and the onset of gametogenesis and subsequent spawning is closely linked to the seasonal changes in the water temperature and food availability in the water column.