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 30oC, 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 4.4x107 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.