Ecological Interdependence of Pollution, Fish Parasites, and Fish in Freshwater Ecosystems of Turkey

Abstract

Records of mass fish deaths were found in different data sources for this study. A map of mass fish deaths in Turkey was also realized for the first time. We aimed to present a review of the distribution of mass fish deaths in the freshwater ecosystems of Turkey, mostly present in the Marmara Region and Aegean Sea Region, where there are intensive industrial and agricultural activities. Fish parasites generally occur in equilibrium with their hosts in natural environments. In the freshwater ecosystems of Turkey, which are highly affected by human activities and have extremely rich natural ichthyofauna, the negative effects of pollution on environmental parameters, which can directly affect the fish, and the emergence and overextension of fish parasites can cause a supplementary synergic direct negative effect transposition in mass fish deaths due to the deterioration of host immunity and to the wounds induced in fish where bacterial, viral, and fungal pathogens can be effective. Finally, these factors can influence the fish rate of survival and skew the structure of fish populations. Mass fish deaths have been frequently reported in Turkey, but are usually only explained by pollution as a single accepted anthropogenic stressor. Together with pollution, a supplementary induced bioecological stressor, the qualitative and quantitative characteristics of the fish parasites’ association variations should be assessed and monitored as potential complex precursor indicators of fish communities’ structural degradation and freshwater ecosystems’ dreadful conditions. Fish parasites as biomonitor species should be used to identify the effects of pollution in Turkish ecosystems, and not only in freshwater ecosystems, in the future. An optimum management plan for freshwater ecosystems should include all the physico-chemical factors, fish parasites, and fish elements involved in permanent assessment and monitoring activities.