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NO54 - 2

Phylogenetic Analysis with Complete Mitochondrial Genome Sequences of Benedenia seriolae Specimens Derived from Japanese Seriola spp.

Satoshi Kawato1, Keigo Kobayashi1, Sho Shirakashi2, Soetsu Yanagi3, Yutaka Fukuda4, Hirofumi Yamashita5, Reiko Nozaki1, Ikuo Hirono1 and Hidehiro Kondo1*

1 Laboratory of Genome Science, Tokyo University of Marine Science and Technology, Tokyo 108-8477, Japan
2 Aquaculture Research Institute, Kindai University, Wakayama 649-2211, Japan
3 Kagoshima Prefectural Fisheries Technology and Development Center, Kagoshima 891-0315, Japan
4 Fisheries Research Division, Oita Prefectural Agriculture, Forestry and Fisheries Research Center, Oita 879-2602, Japan
5 Fisheries Research Center, Ehime Research Institute of Agriculture, Forestry and Fisheries, Ehime 798-0104, Japan

(Received April 25, 2019)

ABSTRACT--Infection with the skin fluke Benedenia seriolae is a serious threat of yellowtail aquaculture. Development of genomic resources and molecular markers for B. seriolae is an essential infrastructure to develop control strategies against B. seriolae infections. As a seminal study to establish the genomic resources of the Japanese B. seriolae populations, we sequenced the complete mitochondrial genome (mitogenome) sequences of 12 B. seriolae specimens collected from four prefectures in Japan. The Japanese B. seriolae mitogenomes were mutually 99% identical, while the identity was 85% when compared to that of an Australian specimen. Furthermore, the gene arrangement in the Japanese B. seriolae mitogenome was slightly different from that in the Australian specimen. The substantial mitogenomic divergence between the Australian and Japanese specimens indicates that B. seriolae is composed of molecularly divergent populations. Variable sites were dispersed in the mitogenome of the Japanese B. seriolae. Phylogenetic relationships among the Japanese B. seriolae specimens did not reflect the host species or geographic distributions within Japan.

Key words: Monogenea, Monopisthocotylea, Capsalidae, ectoparasite, mitochondrial genome

Mortality of Spats of Manila Clam Ruditapes philippinarum Experimentally Challenged with the Protozoan Parasite Perkinsus olseni

Tsukasa Waki and Tomoyoshi Yoshinaga*

Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan

(Received February 2, 2019)

ABSTRACT--In a previous field survey of Perkinsus olseni in Manila clams in a tidal flat contaminated with the parasite, the parasite was not detected in spats smaller than 2 mm in shell length collected between April and June. To understand the reason, we undertook an experimental challenge, exposing clam spats to the zoospores of parasite. The spats became infected and began to die when mean infection intensity reached about 106 cells/g soft tissue. Our results, in conjunction with previously reported filtration rates of Manila clams, suggest the absence of infected spats was attributable to clams' low filtration and low zoospore densities.

Key words: Perkinsus olseni, parasite, Manila clam, Ruditapes philippinarum, spat

A Novel PCR-RFLP Genotyping of Flavobacterium psychrophilum Targeting the gyrB Region

Shotaro Izumi1*, Hajime Arai2*, Kyuma Suzuki2 and Futoshi Aranishi3

1 School of Marine Science and Technology, Tokai University, Shimizu, Shizuoka 424-8610, Japan
2 Gunma Prefectural Fisheries Experiment Station, Shikishima, Maebashi, Gunma 371-0036, Japan
3 Institute of Agricultural and Life Sciences, Shimane University, Matsue, Shimane 690-8504, Japan

(Received April 5, 2019)

ABSTRACT--A novel PCR-RFLP typing method was developed using PCR primers specific for the B subunit of DNA gyrase gene (gyrB) of Flavobacterium psychrophilum and restriction endonuclease Bsp119I. With this PCR-RFLP, 300 isolates of F. psychrophilum were classified into two genotypes (197 and 103 isolates), and the respective genotypes were correlated with the host fish species from which the isolates were derived. These isolates were further subdivided into 12 genotypes by combining with three previous PCR-RFLPs. It is suggested that this PCR-RFLP typing system can be a useful tool in epizootiological studies on bacterial cold-water disease.

Key words: Flavobacterium psychrophilum, PCR-RFLP, gyrB, bacterial cold-water disease