Effects of multiple stressors in fish: how parasites and contaminants interact

Abstract

Interest in local environmental conditions and the occurrence and behaviour of parasites has increased over the last 3 decades, leading to the discipline of Environmental Parasitology. The aim of this discipline is to investigate how anthropogenically altered environmental factors influence the occurrence of parasites and how the combined effects of pollutants and parasites affect the health of their hosts. Accordingly, in this paper, we provide an overview of the direct and indirect effects of pollutants on the occurrence and distribution of fish parasites. However, based on current knowledge, it is difficult to draw general conclusions about these interdependencies, as the effects of pollutants on free-living (larval) parasite stages, as well as their effects on ectoparasites, depend on the pollutant-host-parasite combination as well as on other environmental factors that can modulate the harmful effects of pollutants. Furthermore, the question of the combined effects of the simultaneous occurrence of parasites and pollutants on the physiology and health of the fish hosts is of interest. For this purpose, we differentiate between the dominance effects of individual stressors over other, additive or synergistically reinforcing effects as well as combined antagonistic effects. For the latter, there are only very few studies, most of which were also carried out on invertebrates, so that this field of research presents itself as very promising for future investigations.

Major drivers of biodiversity loss and their impacts on helminth parasite populations and communities

“…The effects of pollution on parasitism have been the subject of numerous reviews (e.g. Khan & Thulin, 1991; Poulin, 1992; Overstreet, 1993; MacKenzie et al , 1995; Lafferty, 1997; MacKenzie, 1999; Williams & MacKenzie, 2003; Sures, 2004, 2008; Marcogliese, 2005; Sures et al , 2017; Sures & Nachev, 2022). Indeed, the question has been examined analytically through the use of meta-analysis (Lafferty, 1997; Blanar et al , 2009; Vidal-Martínez et al , 2010; Gilbert & Avenant-Oldewage, 2021), although the latter only considered monogeneans.…”

“…Sures et al (2017) provided the most recent comprehensive review of effects of pollution on parasites, an aspect of a broader area of study they refer to as ‘environmental parasitology.’ Generally, effects of contaminants on parasites are often negative and can be direct, as on ectoparasites and free-living stages, or indirect, acting on the intermediate and definitive hosts of endoparasites (Sures et al , 2017; Sures & Nachev, 2022). There have been several studies on pollution and parasites since that review, and a few are deserving of special mention.…”

Parasites and Pollutants: Effects of Multiple Stressors on Aquatic Organisms

“…The cystacanth larvae (Figure 3B) often manipulate the behaviour of their invertebrate intermediate host by interfering with host physiology to enhance the trophic transmission to the final host (Helluy, 2013) and thereby execute a variety of physiological effects (e.g., Bailly et al, 2018; Bakker et al, 2017; Bollache et al, 2000; Cornet, 2011), which might also be important for ecotoxicological studies (Grabner & Sures, 2019). Adult acanthocephalans (Figure 3C) are known to accumulate enormous amounts of metals inside their bodies, often exceeding the concentrations detected in the organs of their fish hosts (Sures & Nachev, 2022). This enormous metal accumulation might even lead to reduced metal concentrations in tissues of infected hosts as compared with uninfected ones (see Sures, Nachev, Selbach, et al, 2017; Sures et al, 2023, and references therein), suggesting that adult acanthocephalans might be beneficial to their hosts under polluted conditions.…”

“…Besides the consumption of host resources, parasites can modulate various host body functions such as the immune and hormone system, metabolism and energy storage, the general stress response (e.g., heat shock protein 70 [hsp70], cortisol), oxidative stress, and other biomarkers (Ford & Fernandes, 2005; Marcogliese & Pietrock, 2011; Minguez et al, 2009; Morley, 2006; Poulin, 1992; Sures, 2006, 2008a, 2008b; Sures, Nachev, Selbach, et al, 2017; Tekmedash et al, 2016). In addition, several parasites can accumulate toxicants and can reduce the tissue concentrations in the host, which might, as a consequence, lead to a different stress response in infected versus uninfected hosts (Nachev & Sures, 2016; Sures & Nachev, 2022; Sures et al, 2023). Before going into details with respect to possible parasite–pollutant interactions and their combined effects on hosts and ecotoxicologically relevant parameters, we will give a brief overview of the most important groups of parasites occurring regularly in selected ecotoxicological target species belonging to crustaceans, molluscs, and fish.…”

Fish parasites (special issue)

“…Bernd Sures and Milen Nachev from Germany reviewed the interactions between pollutants and parasites (Sures and Nachev, 2022). They show that parasites must be regarded as organisms that are in close mutual exchange with pollutants.…”