History and Management of the Parasite Fauna of Aral Sea Fishes

The present study reviews the parasite fauna of fishes in the Aral Sea, before, during and after the recent regression and salinization crisis. The native fish fauna was much depleted compared to the nearby Caspian Sea, comprising only 20 spp., all having a freshwater origin. The parasite fauna was similarly poorer, both in total species number and when considering parasites infesting individual species. Some fish species and parasites were introduced during the 20^th century. Species introduction of fish and progressive salinization in the latter half of the 20^th century interacted in various ways, occasionally favouring the spread of parasites. During the salinization parasites with endoparasitic lifecycles endured longer than many ectoparasites, the latter being constantly exposed to the salty water. But all parasites eventually suffered when the salinity tolerance of their free-swimming larvae was exceeded. Predation on zooplankton by introduced fish also temporarily impacted the free larvae of crustacean parasites, causing a decline. Alternatively, introduced fish that were prey to larger species could act to transmit parasites. All the parasites in the southern Large Aral Sea ultimately disappeared, either because their hosts were gone or because of an inability to endure high salinity. Many of the original fish species have now naturally repopulated the reconstituted Small Aral Sea, forming the basis of a renewed commercial fishery. As a result, some parts of the original parasite fauna have also reappeared together with some newly introduced species. The present study highlights the complex, sometimes unexpected, manner in which hosts and parasites can interact during a progressive ecological crisis. We emphasize that they must be an integral part of any sustainable ecological management of lakes and reservoirs. In the framework of revived fisheries and emerging aquaculture, we suggest a system for sound monitoring and control of fish parasites in the Aral Sea system.