Impact of low-level water pollution on some biological aspects of redbelly tilapia (Coptodon zillii) in River Nile, Egypt

Abstract

Mortality of fish has long been recognized as the evident indication of pollution, nevertheless, the increasing low-level pollution may lead to a long-term decline and eventual extinction of fish stocks. This study investigates the impact of a point source pollution (El-Sail Drain) on the biological parameters of redbelly tilapia (Coptodon zillii) in the River Nile at Aswan, Egypt. The present results showed a significant variation of the physicochemical parameters and heavy metals of the River Nile waters in the vicinity of El-Sail Drain. On the other hand, metal concentrations in the gonads of C. zillii from the downstream of the pollution source were significantly higher than that of the unimpacted upstream area. The sex ratios of C. zillii varied in the two studied areas, where it was 1:1.38 in the unimpacted area and was 1:0.9 in the impacted area. While the GSI values of the impacted area were decreased significantly (p < 0.01) compared to that of the unimpacted area. As well, the fecundity of C. zillii was found to decrease due to their exposure to various metals in the impacted area. Based on the results of the present study, the evidenced low-level water pollution from El-Sail Drain was found to affect negatively the biological and reproduction features of C. zillii.

Keywords

• Heavy metals
• Condition factor
• Gonadosomatic index
• Hepatosomatic index
• Fecundity
• Sex ratio