A comparative analysis was made of the population of commercial shrimp (Family Penaeidae) inhabiting the south-eastern part of the Mediterranean Sea during the last 20 years. The changes in biological and oceanographic conditions that occurred after regulation of the Nile flow (1965) had a direct effect on the Egyptian shrimp fishery. That effect was clear in the general decrease of annual shrimp yields, in the changes of species composition and distribution, and in the changes of seasonal accumulation. The small-size species of the Family Penaeidae such as Metapenaeus stebbingi, Trachypenaeus curvirostris and Parapenaeus longirostris constituted the main bulk of shrimp yield in this period, while the larger-size species such as Penaeus japonicus, Penaeus kerathurus, Penaeus semisulcatus and Metapenaeus monoceros showed a sharp decrease in numbers.