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Freeman M.A.,University of Malaya | Freeman M.A.,University of Stirling | Eydal M.,University of Iceland | Yoshimizu M.,Hokkaido University | And 4 more authors.
Parasites and Vectors | Year: 2011

Background: Epidermal pseudotumours from Hippoglossoides dubius and Acanthogobius flavimanus in Japan and gill lesions in Limanda limanda from the UK have been shown to be caused by phylogenetically related protozoan parasites, known collectively as X-cells. However, the phylogenetic position of the X-cell group is not well supported within any of the existing protozoan phyla and they are currently thought to be members of the Alveolata. Ultrastructural features of X-cells in fish pseudotumours are somewhat limited and no typical environmental stages, such as spores or flagellated cells, have been observed. The life cycles for these parasites have not been demonstrated and it remains unknown how transmission to a new host occurs. In the present study, pseudobranchial pseudotumours from Atlantic cod, Gadus morhua, in Iceland and epidermal pseudotumours from the northern black flounder, Pseudopleuronectes obscurus, in Japan were used in experimental transmission studies to establish whether direct transmission of the parasite is achievable. In addition, X-cells from Atlantic cod were sequenced to confirm whether they are phylogenetically related to other X-cells and epidermal pseudotumours from the northern black flounder were analysed to establish whether the same parasite is responsible for infecting different flatfish species in Japan. Results: Phylogenetic analyses of small subunit ribosomal DNA (SSU rDNA) sequence data from Atlantic cod X-cells show that they are a related parasite that occupies a basal position to the clade containing other X-cell parasites. The X-cell parasite causing epidermal pseudotumours in P. obscurus is the same parasite that causes pseudotumours in H. dubius. Direct, fish to fish, transmission of the X-cell parasites used in this study, via oral feeding or injection, was not achieved. Non-amoeboid X-cells are contained within discrete sac-like structures that are loosely attached to epidermal pseudotumours in flatfish; these X-cells are able to tolerate exposure to seawater. A sensitive nested PCR assay was developed for the sub clinical detection of both parasites and to assist in future life cycle studies. PCR revealed that the parasite in P. obscurus was detectable in non-pseudotumourous areas of fish that had pseudotumours present in other areas of the body. Conclusions: The inability to successfully transmit both parasites in this study suggests that either host detachment combined with a period of independent development or an alternate host is required to complete the life cycle for X-cell parasites. Phylogenetic analyses of SSU rDNA confirm a monophyletic grouping for all sequenced X-cell parasites, but do not robustly support their placement within any established protist phylum. Analysis of SSU rDNA from X-cells in Japanese flatfish reveals that the same parasite can infect more than one species of fish. © 2011 Freeman et al; licensee BioMed Central Ltd.

Takeda T.,Hokkaido Abashiri Fisheries Experiment Station | Takeda T.,Central Fisheries Research Institute | Akino M.,Hokkaido Abashiri Fisheries Experiment Station | Imamura T.,Hokkaido Central Fisheries Experiment Station | Nozawa H.,Hokkaido University
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2010

Rigor mortis of the adductor muscle in the scallop Patinopecten yessoensis is a serious quality control problem for the distribution of scallop products. We aimed to develop technologies to delay the rigor mortis of the adductor muscle in scallops. We investigated what factors were involved in the rigor mortis during the storage period after removal of the adductor muscle from the scallop shell, especially the effects of energy recovery during the process of preserving live individual scallops on the quality of the adductor muscle. We also examined effective conditions for preserving the scallops to recover their energy levels. We found that the arginine phosphate concentration in the adductor muscle was important with respect to rigor mortis but not ATP concentration. We also found that it was necessary to preserve the scallop just after harvesting at low temperature and with sufficient oxygen supply, to recover the arginine phosphate concentration lost during the process of harvesting and then leaving the scallops in air.

Shimoda K.,Hokkaido Fish Hatchery | Shinriki Y.,Hokkaido Fish Hatchery | Kasugai K.,Hokkaido Central Fisheries Experiment Station | Hoshino N.,Hokkaido Fish Hatchery
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2010

The variation in morphological characteristics of adult pink salmon Oncorhynchus gorbuscha collected in nine rivers in Hokkaido, Japan was surveyed in 2005 and 2006. Results of the cluster analysis and discriminant analysis suggested that the difference in meristic counts between the years was greater than that among rivers. The difference in the numbers of dorsal fin rays, anal fin rays and vertebrae between years was greater than that among rivers within year. There was a significant difference in the count of pectoral fin rays and gill rakers of the specimens among rivers, but not between years. Principal component analysis revealed that the 2006 year fish have more dorsal fin rays, anal fin rays and vertebrae, than the 2005 year fish.

Shimada H.,Hokkaido Central Fisheries Experiment Station | Sawada M.,Hokkaido Central Fisheries Experiment Station | Kuribayashi T.,Hokkaido Central Fisheries Experiment Station | Nakata A.,Hokkaido Central Fisheries Experiment Station | And 2 more authors.
Plankton and Benthos Research | Year: 2010

To investigate the mechanisms influencing the spatial distribution of the toxic dinoflagellate Alexandrium tamarense in the Okhotsk Sea off Hokkaido, Japan, intensive field surveys were conducted at 34-37 stations in late July every year from in 2002-2007. Alexandrium tamarense occurred every year. However, the abundance of A. tamarense fluctuated year by year, with extremely low cell densities of A. tamarense in 2005. High abundances of A. tamarense were found frequently in the oceanic area of the surface low-salinity water (LSW, salinity 32.5) and the mixed water (MW). Low abundances were found along the coastal area of the Soya Warm Current (SWC, salinity 33.6) and in the dichothermal water (DTW, temperature 2°C) in the layer of oceanic areas deeper than 30m. The PO 4-P concentration in each water mass was in the order DTW MW LSW SWC and the lowest PO 4-P concentration that occurred in the SWC is considered to be a potential limiting factor for the growth of A. tamarense. The reason for the low A. tamarense abundance in the DTW is considered to be the low water temperature and low light intensity. It is concluded that the water mass of LSW has favorable conditions for the growth of A. tamarense. The relative frequency of each water mass fluctuated every year and the results suggest that the frequency of occurrence of the LSW and MW is one of the most significant factors controlling the abundance of A. tamarense in the area. © The Japanese Association of Benthology.

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