Kumagai Akira, Suto Atsushi, Ito Hiroshi, Tanabe Toru, Takahashi Kiyotaka, Kamaishi Takashi, Miwa Satoshi
Miyagi Prefecture Fisheries Technology Institute, Ishinomaki, Miyagi 986-2135, Japan.
Dis Aquat Organ. 2010 Jul 1;90(3):223-34. doi: 10.3354/dao02228.
Since 2007, mass mortalities of cultured ascidians Halocynthia roretzi (Drasche) have occurred in Miyagi Prefecture, Japan. The mortalities occur from November through August, and the tunics of affected animals become abnormally weak and soft. The number of farming areas where mass mortalities have occurred has increased rapidly: 3 in 2007, 6 in 2008, and 14 in 2009. When an outbreak of the disease occurred, mortality reached 17 to 100%. Prominent histopathological changes in the diseased ascidians were found in the tunics; the tunics of affected animals were usually much thinner than those of healthy individuals, and the tunic matrix showed marked disintegration with irregular arrangements of fiber layers or the presence of hollow spaces. In addition, flagellate-like cells (10-14 microm x 2-3 microm) stained with hematoxylin were observed in the tunics of 31 out of 36 diseased animals (86%), but not in apparently healthy animals (n=38). Experimental infection with the disease was successfully conducted by immersing small pieces of tunic samples from diseased ascidians into aquaria with healthy ascidians. The flagellate-like cells were confirmed in the tunics of all the experimentally infected animals. These results indicate that the mass mortalities of ascidians accompanied by abnormally softened tunics were caused by an infectious agent, and suggest the involvement of the flagellate-like cells in the disease.
自2007年以来，日本宫城县养殖的罗非海鞘（Drasche）出现了大规模死亡现象。死亡现象发生在11月至次年8月，患病动物的被囊变得异常脆弱和柔软。发生大规模死亡的养殖区域数量迅速增加：2007年为3个，2008年为6个，2009年为14个。疾病爆发时，死亡率达到17%至100%。患病海鞘的显著组织病理学变化出现在被囊中；患病动物的被囊通常比健康个体的薄得多，被囊基质显示出明显的崩解，纤维层排列不规则或存在中空空间。此外，在36只患病动物中的31只（86%）的被囊中观察到用苏木精染色的鞭毛虫样细胞（10 - 14微米×2 - 3微米），但在明显健康的动物（n = 38）中未观察到。通过将患病海鞘的小块被囊样本浸入装有健康海鞘的水族箱中，成功进行了该疾病的实验性感染。在所有实验感染动物的被囊中都证实了鞭毛虫样细胞的存在。这些结果表明，伴有被囊异常软化的海鞘大规模死亡是由一种传染性病原体引起的，并表明鞭毛虫样细胞与该疾病有关。
