Khan R A, Thulin J
Department of Biology and Ocean Sciences Centre, Memorial University of Newfoundland, St John's, Canada.
Adv Parasitol. 1991;30:201-38. doi: 10.1016/s0065-308x(08)60309-7.
We have tried to draw attention to an increasing body of evidence (from several publications) that parasites of fish might be useful indicators of pollution. Several types of pollutants, including domestic sewage, pesticides, polychlorinated biphenyls, heavy metals, pulp and paper effluents, petroleum aromatic hydrocarbons, acid rain, and others, are known to affect aquatic animals. Many of the latter are parasitized and, under natural environmental conditions, most fish parasites are believed to cause little or no harm. However, chronic exposure to pollutants over a period of time causes biochemical, physiological and behavioural host changes that ultimately can influence the prevalence and intensity of parasitism. Some of these changes include host nutrition, growth and reproduction. Macroscopic lesions might not always be apparent, but subtle disorders in several specific tissues and organs might occur. Pollutants might promote increased parasitism in aquatic animals, especially fish, by impairing the host's immune response or favouring the survival and reproduction of the intermediate hosts. Alternatively, decreased parasitism might ensue through toxicity of the pollutant to free-living stages and intermediate hosts or by alteration of the host's physiology. Experimental studies indicate that the numbers of ectoparasites such as trichodinid ciliates and monogeneans increase significantly on the gills following exposure to a pollutant, and this is supported by field data on other ciliates and monogeneans where evidence of pollution has been clearly demonstrated. There is also evidence that endoparasitic protozoons, such as myxozoons, microsporans and haematozoons, all of which are capable of proliferating in their hosts, increase substantially in prevalence and intensity when interacting with pollutants. The period of patency might also be prolonged in haematozoan infections. Most reports of pollution effects on endoparasites suggest increased parasitism in fish hosts. This also applies to fish living in areas which receive thermal effluents. Parasites might in turn enhance their hosts' susceptibility to pollutants, and information in support of this view is accumulating. Finally, immunosuppression represents one of the underlying mechanisms influencing increased parasitism. Thus, while published information suggests more than a casual connection between fish parasites and pollution, further research is needed to establish the cause-and-effect relationship and at the same time take cognizance of histopathological effects of the toxic agents and their concentrations in water. Areas for future research are recommended.
我们试图让人们关注越来越多的证据（来自多篇出版物）表明，鱼类寄生虫可能是污染的有用指示生物。已知包括生活污水、农药、多氯联苯、重金属、纸浆和造纸废水、石油芳烃、酸雨等多种污染物会影响水生动物。许多水生动物会被寄生，在自然环境条件下，大多数鱼类寄生虫被认为几乎不会造成危害或根本无害。然而，长期接触污染物会导致宿主发生生化、生理和行为变化，最终可能影响寄生的流行程度和强度。其中一些变化包括宿主的营养、生长和繁殖。宏观病变可能并不总是明显的，但某些特定组织和器官可能会出现细微的紊乱。污染物可能通过损害宿主的免疫反应或有利于中间宿主的生存和繁殖，从而促使水生动物尤其是鱼类的寄生现象增加。或者，污染物对自由生活阶段和中间宿主的毒性作用，或宿主生理机能的改变，可能导致寄生现象减少。实验研究表明，接触污染物后，鳃上的外寄生虫如车轮虫和单殖吸虫的数量会显著增加，其他纤毛虫和单殖吸虫的现场数据也支持了这一点（在这些现场数据中，污染证据已得到明确证实）。也有证据表明，内寄生原生动物，如粘孢子虫、微孢子虫和血孢子虫，所有这些都能够在宿主体内增殖，在与污染物相互作用时，其流行程度和强度会大幅增加。血孢子虫感染的开放期也可能延长。大多数关于污染对内寄生虫影响的报告表明鱼类宿主中的寄生现象增加。这也适用于生活在接收热废水区域的鱼类。寄生虫反过来可能会增强其宿主对污染物的易感性，支持这一观点的信息正在不断积累。最后，免疫抑制是影响寄生现象增加的潜在机制之一。因此，虽然已发表的信息表明鱼类寄生虫与污染之间存在的不仅仅是偶然联系，但仍需要进一步研究来确定因果关系，同时要认识到有毒物质的组织病理学效应及其在水中的浓度。本文还推荐了未来的研究领域。
