Spatial Variability in Growth and Condition of Nile Tilapia <i>Oreochromis Niloticus</i> Linked to Pollution Gradients in the Nile River, Egypt

Abstract

Abstract This study investigated spatial variations in growth, condition factor, age, and longevity of Oreochromis niloticus populations along a pollution gradient in the Nile River, Aswan, Egypt. We compared a reference site (Ferial, Site I) with two polluted sites: El-Sail Drain (Site II) and Kom Ombo (Site III). Water and fish samples were collected monthly from January to December 2021 to analyze physicochemical parameters, heavy metals, age structure, growth, and condition factor. The results revealed significant spatial disparities. Fish from Site I exhibited the highest growth potential, with an asymptotic length ( L ∞ ) of 27.22 cm, a growth coefficient (K) of 0.17 year −1 , and a maximum age of 13.5 years. In contrast, populations from Site II and Site III showed reduced growth ( L ∞ = 25.46 and 24.52 cm, respectively), higher K values (0.19 and 0.24 year −1 , respectively), and shorter lifespans (11.9 and 9.2 years, respectively). Although the growth performance index (Ø) was similar among sites, annual length increments and condition factors were significantly lower at the polluted sites. These findings demonstrate that environmental degradation, primarily from industrial and domestic wastewater, adversely affects the somatic growth and physiological conditions of O. niloticus , highlighting the urgent need for enhanced pollution control and management strategies in the Nile River.