Physiological responses and histological alterations induced by pollution in the Nile tilapia from the Rosetta branch of the River Nile, Egypt

The Nile River is the primary source of freshwater in Egypt and supports nearly all the anthropogenic activities in the region and, consequently, it is highly susceptible to pollution from diverse sources. Aquatic ecosystems in the Nile basin face increasing threats originated from pollution and seasonal fluctuations, both of which can profoundly affect the health and resilience of fish populations. Hence, addressing this issue is a must. This study investigated the impact of heavy metals (Fe, Zn, Cu, Cr and Cd) on key physiological and biochemical parameters for the Nile tilapia, Oreochromis niloticus sampled from two sites on the Rosetta Branch of the River Nile: El-Qanater (reference site) and El-Qatta (polluted site) during summer and winter of 2023. In addition, histological analysis was conducted on vital organs covering the winter season. Both site and season were detected with impacts on the hormonal concentrations in the fish samples. Compared to the reference site, fish individuals from the polluted site exhibited pronounced alterations in hormonal balance, with elevated cortisol levels and a marked decline in thyroid hormones (T3 and T4), while TSH levels were increased, particularly during winter. Elevated serum glucose, total protein, and albumin levels were evidenced for metabolic stress. Liver enzyme activity (ALT and AST) and kidney function biomarkers (urea, uric acid, and creatinine) were significantly increased, especially in winter. Profound responses to pollution were recorded with higher levels of SOD, CAT, GPx, and GST, aligned with a substantial decline in GSH levels. Moreover, higher malondialdehyde (MDA) levels were detected in winter. For fish organs histologically examined, a severe damage was remarkably observed in liver, gills, and kidney of fish from El-Qatta site. This study reveals the combined impact of pollution and seasonal changes on the Nile tilapia health, emphasizing the need for continuous monitoring and effective pollution control. Implementing targeted water quality programs in the Rosetta Branch is recommended to preserve fish health, biodiversity, and sustainable fisheries.