The use of fish metabolic, pathological and parasitological indices in pollution monitoring

Abstract

The complex interactions between parasites, hosts and the environment are influenced by the stability of the ecosystem. Heteroxenous parasites, with complex, multiple-host life cycles, can persist only in habitats where the full range of their required hosts are present. Conversely, in impoverished environments such as those impacted by environmental stress, monoxenous species that have simple, single-host life cycles are likely to predominate. In the present study, we analyzed the ratio between heteroxenous and monoxenous (H/M) parasites as well as parasite species richness (S H /S M ) and species diversity in rabbitfish (Siganus rivulatus) collected from several sites in the Red Sea. The rabbitfish is a Suez Canal immigrant, well established in the eastern Mediterranean, and fish were also collected from a site on the Mediterranean coast of Israel. Separate treatment of the micro-and macroparasite components of the rabbitfish parasite communities in the Red Sea suggested that macroparasites only -monogenea and gut parasites -were better indicators than the parasite community as a whole. Quantification of macroparasites is accurate, saves time and effort, produces more accurate data and better differentiates between sites. Higher H/M ratios and S H /S M ratios were found in the rabbitfish collected at the ecologically stable habitat of the coral reef compared to rabbitfish from sandy habitat or mariculture-impacted sandy habitat. The results of the study emphasized the negative impacts of cage mariculture on the environment. The rabbitfish collected near the mariculture farms supported the poorest and least diverse parasite communities of all sampled sites, with virtual depletion of heteroxenous species, and even reduction of gill monogenean infections on the hosts. When results from the Mediterranean sites were compared with those of the Red Sea, the data showed full representation of monoxenous parasites (all but one of Red Sea origin), while heteroxenous species were completely absent. We may therefore regard the Mediterranean as a simulation model for a severely environmentally deteriorated, impoverished habitat, in which all or part of the intermediate host species have been depleted, enabling survival of the monoxenous parasite species only. Parasitological investigations were supplemented by testing the activity of cytochrome P 450-dependent mono-oxygenase EROD as a measure of exposure, and lysosomal stability as a measure of toxic effect in the liver of rabbitfish. The results underline the parasitological findings, showing that fish caught at the impacted sandy beach location in the Red Sea have significantly higher EROD activity and a decreased membrane stability compared with animals from the coral reef. In comparison, EROD activity values in rabbitfish from the Mediterranean Sea were double, while lysosomal membrane stability was half that measured at the most impacted Red Sea location.

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“…We presume that these two parasites have been carried into the Mediterranean on their Erythrean immigrant hosts. Co-invasion of the fish and their parasites has previously been reported for parasitic copepods, gill parasitic monogeneans and for endoparasitic digeneans on fish hosts (Fischthal, 1980;Diamant et al, 1999;Pasternak et al, 2007;ElRashidy and Boxshall, 2010;. In addition to coinvasion of parasites and their hosts, the phenomenon of host switching of some parasitic copepods was reported by El-Rashidy and Boxshall (2010 …”

Environmental Parasitology. Interactions between parasites and pollutants in the aquatic environment

“…Generally, infections with ectoparasites tend to increase, whereas infections with endoparasitic helminths tend to decrease with increasing levels of pollution (Sures, 2005). Differences in the susceptibility of heteroxenous and monoxenous parasites can be used to indicate environmental pollution by calculating the ratio of the sums of heteroxenous and monoxenous (H/M) parasite individuals per host, as well as the ratio of heteroxenous and monoxenous parasite species richness found on the host fish (S H /S M ) as suggested by Diamant et al (1999). The authors found higher H/M ratios and higher S H /S M species richness ratios when comparing parasite communities of rabbitfish (Siganus rivulatus) sampled from an ecologically stable habitat of the Red Sea as compared with the community of fish sampled from anthropogenically impacted environments.…”

Parasites of the grouper fishEpinephelus coioides(Serranidae) as potential environmental indicators in Indonesian coastal ecosystems

“…Fish parasites have been used as biological and environmental indicators (for a review see Palm, 2011), especially for environmental change and pollution (Diamant et al, 1999;Dzikowski et al, 2003;Palm & Rü ckert, 2009) or environmental stress (Landsberg et al, 1998). Sures (2001Sures ( , 2003 used acanthocephalan parasites to detect heavy metal pollution, because acanthocephalans accumulate 1000 times higher amounts of heavy metals in contrast to their host tissues.…”