海湾扇贝养殖过程中的流行病学调查研究

2001~2002年,对莱州湾养殖海湾扇贝进行了较系统地流行病学调查研究.以海湾扇贝养殖集中海区莱州市金城镇扇贝养殖场为定点调查和样品采集点.调查内容主要包括海湾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,盐度等理化环境因子进行连续监测.调查结果显示:海湾扇贝在0.5~1.3cm的幼贝阶段死亡率较高,达50%;随后死亡率降低,1.3~2.2cm的幼贝阶段死亡率约为20%,以后各阶段死亡率平稳,均在7%以下,累积死亡率约为60%.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;温度变化与死亡率有一定的相关性,即低温(20℃以下)可能是养殖海湾扇贝幼贝重要的环境胁迫因子,而高温(27℃左右)对海湾扇贝成贝生长无不良影响.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,海湾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,即0.5,1.5,3.0,3.6和5.0cm的海湾扇贝RLO的感染率分别为15%,35%,80%,50%和20%;RLO的感染强度分别为1.0,1.5,16.0,11.5和5.0.在病原生物检查过程中,除RLO以外还发现有类支原体原核生物(MLO)寄生.结合感染强度和组织病理学的相关性分析,初步认为类立克次体(RLO)可能是海湾扇贝在海上吊养的幼贝阶段发病死亡的致病因子.

Epizootiological study on mass mortalities of the cultured scallops Argopecten irradians

A systemic epizootiological study on mass mortalities of the cultured sea scallop Argopecten irradians was carried out during the period of 2001~2002. The results show that the mortality rate of the juvenile population of A.irradians is about 60% from June to October, with the death peak occurring in June. The results on investigation of environmental factors revealed that the lower water temperature might be the serious stress factor to the cultured juvenile populations of A. irradians. Several suspicious pathogens infecting the scallop were found such as rickettsia-like organism (RLO), mycoplasma-like organism (MLO). The results of histological observation showed that rickettsia-like organism inclusions were common, histological widespread infective agent. The averaged prevalence was from 15%~80% among cultured juvenile populations with averaged sizes of 0.5~5 cm.The highest infection intensity of RLO was from averaged 11.5 to 16 inclusions per section during the death peak of juvenile populations.An inference is made from the above analysis that RLO infection is positively correlated with mortality rates of juvenile populations and may be the main pathogen responsible for mass mortalities of the cultured juvenile populations of scallop, A.irradians on the basis of the observation of intensity of RLO infection and host pathology.