Are Juvenile Manila Clam Ruditapes philippinarum Free from Perkinsus olseni Infection in Korean Waters?
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Note pISSN 1738-5261 eISSN 2005-7172
Are Juvenile Manila Clam Ruditapes philippinarum Free from Perkinsus olseni Infection in Korean Waters? Hye-Mi Lee1, Young-Ghan Cho1, Hee-Do Jeung2, Min-Seok Jang3, Jee Youn Hwang4, and Kwang-Sik Choi1* 1
Department of Marine Life Science (BK21 FOUR) and Marine Science Institute, Jeju National University, Jeju 63243, Korea Tidal Flat Research Center, National Institute of Fisheries Science, Kunsan 54014, Korea 3 South Sea Fisheries Research Institute, National Institute of Fisheries Science, Yeosu 59780, Korea 4 Aquatic Disease Control Division, National Institute of Fisheries Science, Busan 46083, Korea 2
Received 5 July 2020; Revised 13 August 2020; Accepted 22 August 2020 © KSO, KIOST and Springer 2020
Abstract − 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 × 10 cells g 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 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. 5
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Keywords − Perkinsus olseni, Ruditapes philippinarum, Manila clam, juvenile, infection prevalence and intensity, RFTM
*Corresponding author. E-mail: [email protected]
1. Introduction Manila clam Ruditapes philippinarum inhabits the temperate muddy and sandy intertidal and shallow subtidal, where the clams burrow into the sediment to maximum of 10 cm from the surface to avoid lethal risks such as predation and desiccation (Kurihara 2003; Toba et al. 2011; Takeuchi et al. 2015). On the west coast of Korea, Manila clam is one of the dominant species in the intertidal benthic community, where the density often exceeds 1,000 indiv
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