Assessing relationships between chemical exposure, parasite infection, fish health, and fish ecological status: A case study using chub (Leuciscus cephalus) in the Bílina River, Czech Republic

Abstract

Multiple stressor scenarios, as they are relevant in many watersheds, call for approaches extending beyond conventional chemical-focused approaches. The present study, investigated the fish population, represented by chub (Leuciscus cephalus), in the Bílina River (Czech Republic), which is impacted by various pollution sources and might pose a risk on the fish population. To confirm or reject this hypothesis it was examined whether there exists an association between abundance of chub and exposure to toxic chemicals as well as natural stressors, represented by parasites, and whether health-related suborganismal traits, namely, organ indices, tissue histopathology, and immune parameters, would help in revealing relationships between stressor impact and population status. Toxic pressure was assessed by the toxic unit approach, which gives an integrative estimate of toxic effect concentrations and by measuring the biomarkers cytochrome P4501A and vitellogenin, which indicate exposure to bioavailable arylhydrocarbon- or estrogen receptor ligands. Parasite pressure was estimated by determining abundance and species composition of ecto- and endoparasites of chub. Chub abundance was high upstream in the Bílina, low to zero in the middle stretches, and increased again downstream. Toxic pressure increased in the downstream direction, while parasite intensity decreased in this direction. Health status of chub did not differ clearly between up-, middle-, and downstream sites. Thus, it appears that neither toxic pressure nor parasite pressure nor their combination translates into a change of chub health status. By using varied assessment tools, this study provides evidence against a presumed causative role of toxicants impairing the fish ecological status of the Bílina River.

Response of Parasite Community Composition to Aquatic Pollution in Common Carp (Cyprinus carpio L.): A Semi-Experimental Study

“…In our study, the less polluted control site was characterized by higher parasite diversity and equitability and lower dominance. This corresponds to findings reported from a range of other freshwater ecosystems, e.g., [47,[49][50][51], and supports the indication value of parasite communities in partially controlled natural studies. The parasite community of carp restocked into the treatment pond (C-T) from the control pond (C-C) adapted quickly to the new environmental conditions and, after six months exposure, matched the composition of those carp in the treatment pond.…”

“…Likewise, a decrease in the diversity and abundance of Dactylogyrus spp. was also found in chub (Squalius cephalus) at downstream sites along an increasing pollution gradient in the River Bilina, Czech Republic [50]. Moreover, Gilbert and Avenant-Oldewage [17] found that the diplozoid Paradiplozoon ichthyoxanthon had disappeared from a polluted site in South Africa within 14 years of the water quality decreasing, despite the plentiful presence of its fish host, while changes in parasite prevalence in the control lake over the same period clearly reflected the parasite's natural seasonal variance.…”

Assessment of polycyclic aromatic hydrocarbon contamination of the Bílina River (Czech Republic) using passive water samplers and fish biliary metabolites

“…The variability in fish occurrence in the Bílina River was documented by Wenger et al (2010). The authors assessed the relationships between chemical exposure, parasite infection, fish health, and ecological status of this area.…”

The Ecological Importance of Amphipod–Parasite Associations for Aquatic Ecosystems

“…The recently established research direction known as "Environmental Parasitology" investigates the different aspects of the interaction of parasitism and environmental stressors, including pollution, providing many studies from the aquatic environment [26,[51][52][53][54][55][56][57]. Frequently, the combined effects of parasites and pollutants on host health are negative and could be additive or synergistic, increasing parasite occurrence and adverse effects [52,55,58,59]. However, effects are sometimes antagonistic, leading to an advantage for infected organisms in which parasites accumulate pollutants and thereby reduce the exposure concentration of the hosts [56,60,61].…”