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At present, repeated occurrence of disease has been the bottle-neck for sustainable development of sea cucumber (Apostichopus japonicus) culture in China, and has been the subject of multiple studies by fishery scientists. Wang et al reported that bacteria, fungi and parasites involved in the skin ulceration and edema in the sea cucumber (7); bacterial diseases in echinoderms, echinoids, holothuroids and asteroids were described by Jangoux (2). Becker et al reported a skin ulceration disease in sea cucumber Holothuria scabra caused by bacterial infection (1). The viruses were observed in the body of the sea cucumber Apostichopus japonicus by Wang et al but they did not confirm whether the viruses were pathogens (6). In this paper, for the first time, we show that the virus is a pathogen of the disease in sea cucumber Apostichopus japonicus. A disease with the symptoms of evisceration and skin ulcerations broke out and led to mass mortality in sea cucumber Apostichopus japonicus cultivated in indoor ponds near the Dalian coast from December 2004 to April 2005, and led to almost 100% mortality. Isolation and identification of the virus as a pathogen and artificial infection was conducted and is described in this paper.
The Syndrome of Sea Cucumber (Apostichopus japonicus) Infected by Virus and Bacteria
- Received Date: 27 February 2007
- Accepted Date: 18 July 2007
Abstract: A outbreak of disease with symptoms of evisceration and skin ulteration led to mass mortality in sea cucumber Apostichopus japonicus cultivated in indoor ponds near the Dalian coast from December 2004 to April 2005. Spherical virus particles with a diameter of 75-200 nm were found in the cytoplasm of cells in the water-system, the alimentary canal and in the respiratory trees of the diseased and dying sea cucumber individuals by electron microscopic observation of ultrathin sections. Examination by negative stained samples revealed that all the diseased sea cucumbers were infected by the virus, while the healthly ones cultivated outside the contagious area were not. Two bacterial strains were also isolated from the diseased animals. When exposed to a medium containing the virus particles, regardless of whether the bacterial suspension was added, healthy sea cucumbers exhibited identical disease symptoms as the ones in the indoor ponds, and had a mortality of 90%-100%. However, when exposed to a medium in which there was only one of the two bacterial strains, 30%-80% of the sea cucumbers were infected and nearly 20% died. Negative staining showed that the viral particles were detected only in the bodies of the tested animals that were exposed to the viral medium. Histopathologically, the diseased sea cucumbers are characterized by karyopycnosis, and disintegration of the endoplasmic reticula and mitochondria in the epithelial cells in the water-system, the respiratory tree and the alimentary canal.