栉孔扇贝大量死亡的流行病学调查研究

2001~2003年,对养殖的栉孔扇贝进行了较系统地流行病学调查研究.以栉孔扇贝养殖集中海区长岛县亚美扇贝养殖场为定点调查和样品采集点.调查内容主要包括栉孔扇贝各养殖期的死亡率和可疑病原生物检测,同时对pH、溶解氧、温度、盐度等环境理化因子进行连续监测.调查结果显示:栉孔扇贝在养殖初期幼贝阶段死亡率较低,随后死亡率逐渐升高,至8月24日月死亡率达最高点71%.9月份以后死亡率开始下降.至10月份累积死亡率达90%以上.对环境理化因子的调查显示,pH、溶解氧、盐度的变化幅度不大,与扇贝死亡率无明显相关性;温度变化与死亡率似有一定的相关性,即高温(月平均23℃以上)可能是养殖栉孔扇贝重要的环境胁迫因子.通过对可疑致病性生物因子的调查研究及病理学观察表明,栉孔扇贝在养殖过程中可感染多种微生物,其中原核微生物类立克次体(RLO)在养殖过程各生长阶段均可检出,其感染率和感染强度与扇贝死亡率呈现一致的趋势.在病原病理检测中,发现RLO的大量感染与组织细胞严重病理损伤密切相关.在病原生物检测过程中,除RLO以外还发现有类枝原体原核生物(MLO)和类病毒(VLP)寄生.RLO的人工感染实验结果说明RLO是栉孔扇贝重要的病原菌.结合感染率和死亡率、感染强度和组织病理学的相关性以及感染实验的结果分析,认为类立克次体(RLO)可能是栉孔扇贝养殖过程中大量死亡的主要致病因子.

Epizootiological study on mass mortality of the cultured scallop Chlamys farreri

A systemic epizootiological study on mass mortalities of the cultured scallop Chlamys farreri was carried out during the period of 2001~2003.The results showed that the accumulated mortality rate of the cultivated scallop Chlamys farreri was very high, more than 90% from April to October, and the dead peak occurred on 24 August,being about 71%.The results on investigation of environmental factors revealed that the higher water temperature, more than 23℃,might be a serious stress factor to the cultured Chlamys farreri.Several suspect pathogens infecting the scallop were found such as rickett sia-like organism (RLO),mycoplasma-like organism (MLO) and virus-like particle (VLP).The results of histological observation showed that rickett sia-like organism inclusions were common, histological widespread infectiveagent.The averaged prevalence was from 20% to 90% among cultured scallop populations with averaged sizes of 2.5~6.1 cm.The highest infection intensity of RLO in host tissues was aver aged 31 inclusions persection.The result of experiment sinfected by purified RLOs showed that RLO was a serious pathogen to the scallop.It is inference that RLO infection was positively correlated with mortality rates of the cultured populations and might be the main pathogen responsible formass mortalities of the cultured population of scallop on the basis of the observation of intensity of natural infection, histological pathology and artificial infection experiment.