Microbiological water quality and bacterial infections among Tilapia fish of Lake Manzala , Egypt

The present study aimed to assess the sanitary quality of water and bacterial infections among Tilapia fish in Lake Manzala. Total viable bacterial counts(TVBCs) in water were low in in Winter and high during Summer. This pattern was in harmony with water temperature in the same seasons. The lowest values of transparency were recorded in the discharge areas of Bahr ElBaqar and Hadous Drains and increased gradually away from these Stations. On the contrary, the bacterial counts decreased in the same direction. The recorded pH values of the studied Lake were on alkaline side. Seasonal increases in pH of Lake Manzala during Winter and Autumn may be due to the high photosynthetic activities, while their Spring and Summer decreases may follow the degradation of organic matter in the sediment by bacteria . On the other hand, the results of the present study revealed that the counts of the bacterial indicators of sewage pollution were high. One hundred pathogenic bacterial isolates representing nine genera were identified to species level. This included, the following suggested names: Esherichia coli (15%), Klebsiella pneumoniae (13%), Pseudomonas aeruginosa (12%), Pseudomonas flourcsence (9%), Salmonella cholerasuis (11%), Shigella sp. (7%), Serratia liquefaciens (8%), Proteus vulgaris (8%), Acinetobacter sp. (8%), and Chryseomonas lutecla(9%). On the other hand, the incidence of pathogenic bacterial isolates (%) and annual bacterial infections which causes damage and loses in Tilapia spp. fish were tabulated. Introduction Lake Manzala occupies the north eastern corner of the Nile Delta between the Mediterranean Sea (North) and Suez Canal (East), while 5 Governorates share the western and southern Lake borders. The lake is presumed to have resulted from the accumulation of the Nile flood water, before the construction of the High Dam, in the low lying land which it occupies. Lake Manzala can be used as stabilization lagoon and nutrient assimilation system. Its capacity is relatively efficient because of its 6 week retention time, high temperature shallow depth and high productivity (Mancy and Ibrahim, 1988). In addition, it is the largest and most economically important of Egypt's coastal lakes where it provides an abundance of fish and an internationally important wintering area for water birds and staging area for migratory birds. Accordingly, the eastern part of the Lake (Ashtum El-Gamil) was declared as a Natural Protectorate in June 1988 (Rabeh,2001). In addition, Lake Manzala is considered to be the most important lake in Egypt; in the year 1979,the fish production was about 75,000 tons and the lake area was about 29,100 fedan. Many factors, such as pollution, and drying of the many parts of the lake, have reduced the fish production significantly, to about 47,500 tons in 1990, when the lake area is19,000 fedans. At present, the fish production can be estimated to be 45,000 ton in 2009(Rashad and Abdel-Azeem, 2010). There are about 12,000 fishermanrepresenting families with a population about60,000 people living around the lake and on the islands. Since pathogens appear intermittently in natural waters at low concentrations, detection and quantification of each pathogenic bacterium is labor-insensitive and not easy to perform for most cases. Therefore, the routine microbiological water analyses are based on the detection of indicator microorganisms which International Journal of Environment & Water