Parasites As Bioindicators Of Environmental Pollution

There are some organisms having the ability of providing information about the environment’s chemical state through their absence or presence. There are certain organisms having been affected less by toxic substances. They have also shown the ability of concentrating inside the tissues with environmental pollutant (Rosenberg & Resh, 1993). With respect to this, although organic pollutants are not accumulated by the parasites, they have the ability of altering the uptake of their hosts’ chemicals, which includes metals (Evans, Irwin, & Fitzpatrick, 2001). The toxic materials of greater concentrations are accumulated by the parasites in their bodies and hence they act as for the fish host the metal sinks and thus aid their survival in toxins’ presence (Sures, 2007). Thus, there is necessity from the viewpoint of the public health in determining the concentrations of heavy metal in the captured fish for the consumption of human (Khan &Thulin, 1991).

In the present study, in Al-Khumrah, the mean infection concentration of Cu is 141.12 mg/kg (gill), 88.74 mg/kg (intestine), 188.70 mg/kg (liver), 94.50 mg/kg (muscles) while the non- infection concentration of heavy metal is 194.99 mg/kg (gill), 82.76 mg/kg (intestine), 190.88 mg/kg (liver), 87.20 mg/kg (muscles). In Al-Mustorah, the mean infection concentration of heavy metal is 50.98 mg/kg (gill), 85.14 mg/kg (intestine), 233.30 mg/kg (liver), 37.81 mg/kg (muscles), while the non- infection concentration of heavy metal is 46.94 mg/kg (gill), 64.90 mg/kg (intestine), 205.25 mg/kg (liver), and 23.48 mg/kg (muscles). In this present study, highest mean concentration of Cu has been found in liver that has been endorsed by the study of Ali et al. (2011) having found the highest metal concentration in liver of Siganus rivulatus . The highest mean concentration of Zn, in the present study, has been also found in liver. However, the findings in this study with Zn contradict with the study by Abul-Naja (1996) which has found highest concentration of Zn in kidney, and then in intestine and then in liver. Abul-Naja (1996) has also found the concentration of Zn to be more than Cd, Cu, and Pb which is not the case in the present study. Highest concentration of Pb has been found in intestine (Al-Khumrah) and liver (Al-Mustorah).

The Pb’s highest concentration has been found in intestine and kidney in emperor fish, L. mahsena. Little accumulation of Pb has been recorded by Moore and Rammamoorth (1984) in the muscles of freshwater and marine fish species. The Pb of low concentration has been found in the marine fishes’ muscles in the coastal areas of Wales and England

Mn has been found to have the highest concentrations in gills in both Al-Khumrah and Al-Mustorah in the current study. Delving into the previous studies, Mn of higher concentrations have been recorded in the liver, gill, and muscles in samples collected in the site of Al-Kumrah. Thus, the previous studies somewhat endorses the current study in this respect.

In general, there is interference of the worms with the regulation, uptake, metabolism, and absorption of the host of the mineral elements. The nourishment and penetration of the host tissues have the occurrence by proteinases such as the secretion of metalloproteinases by plerocercoids, cercariae, adult trematodes, and adult nematodes (Dzik, 2005). In accordance with it, the helminth’s presence can be altering the fish’s metabolic and physiological function (Azmat et al., 2008).

The host and its parasite compete for a number of elements such as Zn, Fe, and Cu. The immunological responses of the host are affected by the parasite with the secretion of cytokine, neuropeptides, or hormones such as factors or molecules directly altering the hormone levels of the host.

The intestinal parasites gets more metals in comparison to the parasites that inhibits the fish body’s other parts. Oyoo-Okoth et al. (2012) have been suggestive that there is interference of cestodes with the role of metal detoxification on the host of metallo-proteins where the metal binding proteins are absorbed with a number of proteins and lipids that have requirement for the metabolic needs. This also explains why in the infected fish the increase of some metals has been compared to the ones that are non-infected.

Nematoda had higher Cu (101.41±47.59 µg/l vs 53.99±38.15 µg/l) and Mn (118.12±20.28 µg/l vs 102.53±36.53 µg/l) concentration compared to Acanthocephala. Nickel concentration was similar in both parasites (0.63 µg/l). Lead and zinc concentration was higher in Acanthocephala than Nematoda.

In marine fish, the adult nematoda infection has minimized the heavy metal’s bioaccumulation in fish organs and tissues. Thus, it has been considered as the heavy metal pollution’s biological indicator (Eissa et al., 2012). Amongst the nematodes, both larvae and adults and adult philometrids of Anisakis has had efficient concentrated metals where other species had no display of concentrating ability to all or have the ability of concentrating to only new metals (Pascual & Abollo, 2003). The larval nematodes with the help of various uptake routes and due to the need of growing fast at the time of their development and thus have a tendency of adsorbing essential elements such as Zn, and Cu through their body (Hassan et al., 2016). To conclude, the nematodes and cestodes have the causation of significant reduction in Zn, and Cu and an insignificant reduction in Pb and Cd concentrations in the fish organs and tissues that are infected.

The fish helminth parasites, acanthocephalans and cestodes in particular have been considered as the sentinel organisms in elucidating in aquatic ecosystems with metal pollution. The concentration of Pb and Cd have considerably higher in muscles, liver, and intestine (Hassanine, Al-Hasawi, Hariri, & Touliabah, 2019) of non-infected fish compared to the infected fish, with the concentrations of Pb have been higher in consistent fashion compared to that of Cd. There is drastic decrease in order for both: muscle, intestine and liver. In this acanthocephalan, the concentration of metal has been much higher compared to that of its fish host.

This shows that the metals level can be reduced by the intestinal helminthes in the L. mahsena organs and tissues. This can have advantage for the hosts that are infected and allows them tolerating certain metals of much higher concentrations. The present results also do confirmation that trematodes, cestodes and nematodes are seemingly the environmental conditions’ good indicators. There is support for this argument that the present study results indicates that also demonstrates these parasites’ ability in accumulating lead, copper, and cadmium. The present results also have shown the marine endoparasites’ usefulness for heavy metal pollution’s early warning indicators’ application. However, eventually, using the parasites as indicators needs greater understanding and information about the parasites’ basic psychological effect at the time of infection, reproduction, and development on their hosts.

References

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