Fish Parasites as Biological Indicators of Metals Pollution in the Aquatic Environments

Abstract In this review the papers concerned with fish parasites that utilized as biological indicators of metals pollution in the aquatic environments and published between 2010 and 2021 were retrieved according to certain inclusion and exclusion criteria. The fish-parasite models in the retrieved publications differed widely, and only five helminthic species were considered as bioindicators with their recurrence evaluated as follows: acanthocephalan and nematodes > cestodes > trematodes > crustacea. The majority of the investigations were focused on freshwater fish. The frequency of examinations into metals bioaccumulation within the host tissues was evaluated as follows: liver and muscles > gut > kidney > gills and gonads > brain and adipose tissue. Cd was the most commonly studied metal, followed by Pb, and the remaining elements being classified as Cu > Zn > Mn > Cr& Fe > Ni > As > Al & Co > Hg, Se, Sn, Ti& V > Mg& Ba. The elements Mo, Pt, Sb, Th, U, and Sr were all tested once. In conclusion, fish parasites can be used as a biological indicator of metal pollution while also reducing metal bioaccumulation in fish tissues, as they can accumulate heavy metals in their tissues at a higher rate than fish tissues. Therefore, the parasites might act as metal biosinks or sentinels in aquatic habitats. In addition, reduced chemical absorption in animals employed in ecotoxicological studies due to parasitic infections, may confuse researchers into believing that pollution levels are minimal.