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Odawara K.,Ehime Research Institute of Agriculture | Yamashita H.,Ehime Research Institute of Agriculture | Sone K.,Ehime Research Institute of Agriculture | Aoki H.,Mie Prefecture Fisheries Research Institute | And 7 more authors.
Fish Pathology | Year: 2011

We evaluated the prevalence of the akoya oyster disease (AOD) in Japan and the pathogenicity of the unidentified causative agent. We obtained naive Japanese pearl oysters Pinctada fucata martensii from a site with no history of AOD. In separate experiments, the oysters were either challenged by intramuscular injection with the hemolymph of infected oysters or reared in several major pearl oyster farms throughout Japan. Both groups of oysters experienced high mortality and exhibited discoloration of the adductor muscle and histopathological changes characterizing AOD. Our data suggest that AOD is prevalent in pearl oyster culture fields throughout Japan and that the causative pathogen remains highly pathogenic to P. fucata martensii. When groups of oysters produced by repeated selective breeding against AOD were reared in different pearl oyster fields alongside uninfected naive oysters, the selectively bred oysters had significantly lower mortality than naive oysters. The recent decline in outbreaks of AOD can be attributed, in part, to the introduction of selectively bred oysters that are resistant to this disease © 2011 The Japanese Society of Fish Pathology.


Aoki K.,Japan National Research Institute of Fisheries Science | Onitsuka G.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Shimizu M.,Japan National Research Institute of Fisheries Science | Yamatogi T.,Nagasaki Prefectural Institute of Fisheries | And 3 more authors.
Marine Pollution Bulletin | Year: 2015

In 2010, a massive bloom of the raphidophycean flagellate Chattonella occurred in the Ariake Sea and Tachibana Bay. Bloom dynamics and hydrographical conditions were examined by field survey. The development and decline of the bloom occurred three times in Tachibana Bay. First and third bloom developments synchronized with precipitation, and the second bloom developed in synchronization with a salinity decrease which occurred in relation to an increase of river discharge from the Chikugo River which takes several days to flow from the Ariake Sea. These results imply that the bloom was transported with the low salinity water from the Ariake Sea to Tachibana Bay. During blooms along the northern coast of Shimabara Peninsula, the predominant phytoplankton species changed from Chattonella to Skeletonema. Low salinity water intrusion induced an interregional difference of the Chattonella and Skeletonema bloom spatially-differentiated by the salinity in the Ariake Sea and Tachibana Bay. © 2015 Elsevier Ltd.


PubMed | Nagasaki Prefectural Tsushima District Fisheries Extension Advisory Center, Japan National Research Institute of Fisheries And Environment of Inland Sea, Japan National Research Institute of Fisheries Science, Nagasaki Prefectural Government and 2 more.
Type: Journal Article | Journal: Marine pollution bulletin | Year: 2015

In 2010, a massive bloom of the raphidophycean flagellate Chattonella occurred in the Ariake Sea and Tachibana Bay. Bloom dynamics and hydrographical conditions were examined by field survey. The development and decline of the bloom occurred three times in Tachibana Bay. First and third bloom developments synchronized with precipitation, and the second bloom developed in synchronization with a salinity decrease which occurred in relation to an increase of river discharge from the Chikugo River which takes several days to flow from the Ariake Sea. These results imply that the bloom was transported with the low salinity water from the Ariake Sea to Tachibana Bay. During blooms along the northern coast of Shimabara Peninsula, the predominant phytoplankton species changed from Chattonella to Skeletonema. Low salinity water intrusion induced an interregional difference of the Chattonella and Skeletonema bloom spatially-differentiated by the salinity in the Ariake Sea and Tachibana Bay.


Aoki K.,Japan National Research Institute of Fisheries Science | Shimizu M.,Fisheries Research and Education Agency | Kuroda H.,Hokkaido National Fisheries Research Institute | Yamatogi T.,Nagasaki Prefectural Institute of Fisheries | And 3 more authors.
Journal of Oceanography | Year: 2016

In both 2009 and 2010, massive Chattonella blooms occurred in Tachibana Bay. Observation results show that high cell densities of Chattonella were distributed in the central area of Tachibana Bay with low salinity water. Model results indicate that the low salinity water originated from the Ariake Sea and intruded into Tachibana Bay during the northerly or weak winds. It is suggested that low salinity water was mainly discharged from the northern area of the Ariake Sea. Northerly wind enhanced the horizontal advection of the low salinity water intruding into Tachibana Bay originating from the northern area of the Ariake Sea. © 2016 The Oceanographic Society of Japan and Springer Japan


Onitsuka T.,Japan National Research Institute of Fisheries Science | Kawamura T.,University of Tokyo | Ohashi S.,Nagasaki Prefectural Institute of Fisheries | Iwanaga S.,Nagasaki Prefectural Institute of Fisheries | And 3 more authors.
Aquaculture | Year: 2011

To elucidate the dietary value of macroalgal gametophytes for post-larval and juvenile abalone Haliotis diversicolor, growth and survival rates of five different size groups of the abalone [1.4-3.4, 2.8-4.6, 4.4-6.0, 5.7-8.3 and 7.6-12.0mm in shell length (SL)] fed on gametophytes of three brown macroalgae (Eisenia bicyclis, Ecklonia cava and Undaria pinnatifida; Laminariales, Phaeophyta) were examined, and compared with those fed a benthic diatom Nitzschia sp. Most abalone actively fed on all algal diets, but large variations in the growth rate were observed among the diets and abalone growth stages. Mean growth rates of abalone fed Nitzschia sp. were similar or higher than those fed the macroalgal gametophytes in 1.4-4.6mm SL, but lower in 4.4-8.3mm SL. For all of the three macroalgal gametophytes, growth rates of the abalone increased linearly from 2-3mm SL and were highest at around 6mm SL. However, mean growth rates of larger individuals (7.6-12.0mm SL) dropped to less than 45μmday-1 in all treatments with the macroalgal or diatom diets. These results indicate that gametophytes of the three brown algae are favorable diets for juvenile H. diversicolor of 3-8mm SL. Introduction of the brown algal gametophytes as diets for juvenile H. diversicolor is considered to be an alternative innovative method to improve the efficiency and stability of the abalone culture. © 2011 Elsevier B.V.

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