Histological observations of the digestive gland of the hard clam Meretrix lusoria and its relation to summer mortality in grow-out cultures in Tokyo Bay, central Japan
2014
Toba, M. (Chiba Prefectural Fisheries Research Center, Futtsu, Chiba (Japan). Tokyo Bay Fisheries Laboratory) | Kobayashi, Y. | Takahashi, Y. | Saito, Y.
Since 2008, mortality of the hard clam Meretrix lusoria was repeatedly observed in grow-out cultures in inter- and sub-tidal areas in Tokyo Bay in summer. To clarify the causes of mortality, we conducted an in situ cage-rearing experiment at five study stations between April and September 2010. In the experiment, the survival and growth of clams were monitored, and clams were sampled periodically for histological observation of the digestive gland. In three of the five stations, i.e., excluding two stations in the Obitsu River estuary, survival of the cage-reared clams was reduced to 1-44% during June-August. Necrosis was found in the epithelial cells of the pretubular duct in a number of clams. The stratified structure of the columnar epithelial cells within the pretubular duct collapsed because of extensive necrosis in some clams. Occurrence of histological abnormalities in the digestive diverticula during the period of high clam mortality indicated that necrosis of the epithelial cells may be related to the cause of the mortality.
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