The fish distribution in Lake Manzalah, the largest of the Delta Lakes of Egypt, was studied and discussed in the light of the prevailing physical and chemical conditions. The lake-sea connection is of vital importance for the welfare of the lake and has a pronounced effect on the its distribution. Many marine forms like Mugil cephalus, M. capito, Sciaena aquilla, Chrysophris aurata, Morone labrax, M. punctata and shrimps can tolerate the brackish water of the lake during certain phases of their life. Tilapia spp., namely Tilapia aurea, T.galilaea, T. nilotica and T. zillii being the principal fish in the lake have different degrees of salinity tolerance. The tolerate limits of different ecological factors like salinity, temperature, pH and dissolved oxygen was determined for different species of fish.