Ecosystem and Commercializing of Fish in a Rich-Minerals, Low-Salinity Closed Lake

Abstract

Wadi El Natrun is an elongated narrow depression in the Western Desert of Egypt. The depression characterized by many ancient alkaline salt lakes. These lakes are filled with water in winter and dried up in summer. Recently, some lakes become permanently dried, while others become submerged throughout the year as El Bieda Lake. El Bieda Lake has undergone ecological changes due to the prolonged extraction of minerals and the continual discharging of freshwater. This study investigates the recent biotic and abiotic changes of this lake and discusses its fisheries opportunities. The lake’s water is well-oxygenated, rich with different inorganic nutrients, and characterized by a low salinity. Sodium and chloride ion concentrations are lower than the equivalent surface seawater, while magnesium, calcium, potassium, sulfate, and bicarbonate ions are higher. The lake has low plankton species richness with high biomass and high nutritional values. More recently, two cichlid species, Oreochromis aureus and Coptodon zillii, have colonized the lake. Summer characterized by a very low mortality for Oreochromis aureus and a poor representation of Coptodon zillii. However, both species shared the catch the rest of the year. The high biomass and nutritional quality of plankton communities, as well as the dense phytobenthic film, indicate that the lake is currently below its carrying capacity. The well-oxygenated water, high biomass of plankton and phytobenthic diatoms, and the expected changes in salinity suggest that introducing the euryhaline, commercially valuable, and fast-growing Mugil cephalus or Chelon ramada in El Bieda Lake is highly advisable.