engleski

The role of fish intestinal parasites (acanthocephalans) in metal exposure assessment and protection of fish against metal accumulation

Metal contamination in aquatic systems is a critical environmental issue due to metal uptake, accumulation and possible toxicity in aquatic organisms. Although there are common and well established indicator organisms and tissues, as well as biomarkers of metal exposure, we are still in need of reliable and sensitive bioindicators to monitor metal pollution in the environment. In the past decades it was shown that fish intestinal parasites, acanthocephalans, can accumulate metals at concentrations that are orders of magnitude higher than those in the commonly used indicator organisms like fishes, bivalves or crustaceans. Accordingly, attempts have been made to utilize acanthocephalans as biological indicators of metal exposure in environmental risk assessment studies. Parasites can cause mechanical (fusion of gill lamellae, tissue replacement), physiological (cell proliferation, immunomodulation, altered growth) and reproductive damage in fishes. Consequently, fishes under the stress of their parasite load are weakened and become more susceptible to other environmental stressors including contaminants. On the other hand, it was reported that parasites might alter metal uptake and accumulation in fish due to high metal accumulation capacity, resulting in reduced metal levels in tissues of infected compared to uninfected hosts. In the present study selected essential (Cu, Fe, Mn, Zn) and non-essential (Ag, Cd, Pb) trace metals were analysed in acanthocephalan Pomphorhynchus laevis and gastrointestinal tissue of European chub (Squalius cephalus L.) from the Sava River in Croatia. The sampling was performed during April/May (chub spawning period) and September (post-spawning period) in order to assess if acanthocephalans can reflect seasonal variability in metal levels of their host. The mean intensity of infection with P. laevis was higher in April/May (4.2) than in September (3.0). Although all measured metal levels in chub gastrointestinal tissue were higher during chub spawning, such seasonal variability was not reflected in P. laevis. The bioconcentration factors (the ratio of metal concentration in the parasites to that in host gastrointestinal tissue), which represent a measure of duration of environmental exposure, were also comparable between seasons and indicated low metal exposure of chubs in the Sava River. In both seasons, Cu and Cd levels were higher in uninfected than chub infected with P. laevis, indicating possible protective role of acanthocephalans against metal accumulation in fish.

European chub; Pomphorhynchus laevis; gastrointestinal tissue; essential/non-essential metals; spawning/postspawning period

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