Comparative study on Lake Manzala in Egypt after and before development and purifications: Ecosystem and biomarkers; biochemical, histopathological and immunohistochemical

Abstract

The present work aims to evaluate the impact of Lake Manzala development, started in 2017, on lake water quality and biomarkers of Lake Oreochromis niloticus and Biomphalaria alexandrina samples from Dakahlia and Port Said during 2021 and compare it with the results of a series of studies concerning the same criteria in Lake Manzala during 2015. Results showed a remarkable increase in water EC, indicating a higher water exchange with the sea, a significant decrease in Pb, Cd, Cu, and Zn levels in water samples, and a remarkable decline in Cd and Pb bioaccumulation in all fish and snail samples. Macroinvertebrate samples showed higher taxa richness than in 2015, indicating biologically improved lake water quality. Results showed no trematode transmission, while there were natural infections in B. alexandrina snails during 2015. Biochemically, liver enzymes and hematological criteria in fish and snail samples during 2021 showed levels nearer to control at Port Said, indicating a less stressed liver and more healthy specimens than in 2015. Histopathological examination of fish organs (except spleen) and snail tissues pointed to their improved tissue architecture in Port Said than that of Dakahlia (2021). However, the 2021 samples were better than those of 2015. The immunohistochemical study showed higher expression of IL-6 in Dakahlia samples than the other samples, denoting higher tissue inflammation and humoral immune response. So, all the examined criteria indicated that Manzala Lake is positively impacted by the developmental and purification process, especially in Port Said.

Keywords: Biochemical parameters; Biomphalaria alexandrina; IL-6; Metals; Oreochromis niloticus; Water quality.