Abstract
Bioindicator value of digenean parasites (Acanthostomum absconditum, Acanthostomum spiniceps and Haplorchoides cahirinus) of silver catfish, Bagrus bajad was assessed by analyzing the concentrations of nine heavy metals (Fe, Zn, Cu, Ni, Cd, Cr, Mn, Co, and Pb) using atomic absorption spectrometry. Additionally, the study compared heavy metals concentrations in four sinks (water, gills, intestine and digenean worms) from two aquatic habitats (the upstream and downstream) of the Damietta Branch of the River Nile from January to December, 2018. The results revealed that iron and manganese were the most abundant metals in water, gills, intestine and digenean worms at both the upstream and downstream aquatic habitats. In addition, the digenean worms of B. bajad inhabiting these two localities accumulated higher amounts of all analyzed heavy metals than water, gills and intestine (especially iron and manganese), except for chromium, the highest level of which was encountered in the gill tissues. The seasonal variations of heavy metals indicated their highest concentration in summer (for water, gills, intestine and digenean worms) and lowest concentration in autumn and winter (for water, gills and intestine), and in winter and spring (for digenean parasites). The results confirmed that the digenean intestinal parasites accumulate heavy metals pollutants in a significant manner and are important model for monitoring pollution.