Monitoring some pathogenic bacteria in water and fish of Lake Qaroun

Abstract

Water quality plays a vital role in the productivity of lake’s fish. Lake Qaroun is exposed to untreated agricultural, domestic and industrial effluents which are considered serious pollutents. This study was conducted to monitor the water quality of the lake and the pathogenic bacteria in the surface water and fish. Physico-chemical parameters of water and bacterial count of water and two types of fish Tilapia zillii and Mugil cephalus were studied. Samples were collected from four sites at certain distances from El-Batts drain in the lake during 2015-2016. Physical characteristics of the water showed that the water temperature varied between 16 and 30°C, pH was alkaline. Water salinity and disolved oxygen decreased near El-Batts drain, while the chemical oxygen demand, amonia and nitrate levels were high due to the pollution and bacterial activity. Bacteriological characteriztion revealed that the bacterial load in the nearest point to El-Batts drain was higher than the other examined sites of lake water. The total and fecal coliform near El-Batts drain exceeded the Egyptian standard limits; it reached 4.4x10 7 in summer. The study revealed that the bacterial pathogens counts in fish were high in mullet species than that of tilapia. Total and fecal coliforms were detected in muscles once during the study period; in spring for tilapia and in summer for mullet fish. The study revealed that Aeromonas hydrophila was the most prevalant pathogen isolated from Tilapia zillii and Mugil cephalus and that 72% of A. hydrophila harboured aerolysin toxin gene. A. hydrophila was detected in muscles of both tilapia and mullet during the four seasons through 12 months, while S. aureus and P. aeruginosa were detected only in summer or spring. The study highlights the hazardous effect of the untreated domestic and industrial drainage wastes on water quality and fish of Lake Qaroun.