Relationship between Heavy Metal Accumulation in Freshwater Fish Hosts and Parasites in Aquatic Environments

Abstract

Certain parasitic species may enhance fish fitness in contaminated environments by bioaccumulating pollutants from their hosts. The fate of trace elements and the combined effects of parasitism and pollution were studied in European perch infected with acanthocephalans Acanthocephalus lucii and cestodes Proteocephalus percae from the water reservoir Ružín in Slovakia. Most trace elements were found at higher levels in parasites than in fish matrices, except for mercury, with the highest levels in the fish muscle. The concentration of toxic mercury in fish muscle exceeded the maximum level allowed in European foodstuffs by more than twice. Notably, higher levels of certain elements in both parasite species corresponded to lower element concentrations in the fish. Similarly, concentrations of certain essential elements were lower at high infection intensities in both parasite species, indicating competitive interactions within the host-parasite system. The high percentage of morphological malformations in the tapeworms suggests a negative impact of toxic elements on parasites. These findings support the idea that intestinal fish parasites may provide benefits to their hosts in dealing with trace elements. Moreover, using fish intestinal parasites as bioindicators of trace element contamination can help identify environmental issues and highlight the relationship between parasitism and ecological conditions.