Maximum Sustainable Yield Estimates from Lake Nasser Fisheries, Egypt with Special Reference to Nile Tilapia Oreochromis niloticus using ASPIC Software

The lakes’ fisheries play an important role in the Egyptian economy. Egyptian lakes face many challenges such as over-fishing, illegal and destructive fishing methods, human activities and pollution which affected the fish production from it. The lakes’ contribution to the Egyptian fish production decreased from about 50% in 80’s to the only 10% during 2017. Lake Nasser, as one of the largest artificial lakes in the world, plays a significant role in Egyptian fisheries. Its mean annual fish production is about 28,000 ton, this constituted 18% of the total fish harvested from Egyptian lakes. The catch and effort data over 15 years were collected from the lake and analyzed to assess its status and to summerize the main problems facing its development and management. Maximum Sustainable Yield of Nasser lake with special reference to the Nile tilapia, the main species in the lake, is estimated based on catch and effort data from 2003 to 2017. The computer software packages of ASPIC had been used. The surplus production model of Schaefer was applied in this study. The obtained results proved the over exploitation situation for the lake fishery and to achieve the sustainability many applicable measures are recommended.

Interspecific and intraspecific differences in pectoral-fins spine morphology in Nile River and Lake Nasser catfishes, Siluriformes

The structure of the pectoral fins spine of 4 catfish species Heterobranchus longifilis, Clarias gariepinus, Chrysichthys auratus, Synodontis schall and Synodontis serratus were described. The fish specimens were collected from Asyut City and Lake Nasser about 319 and 900 Km south of the capital Cairo, Egypt respectively on 10 November 2017 are described. The species examined showed variation in the shape of the spine-shaft tip varies from finely to broadly and rounded pointed; the curvature of the spine-shaft is either straight or curved partially or complete; the anterior serrae varies between is either broad or irregular; the anterior ridge groove is well developed, deep, and curved, with some pores in some species; the anterior dentations varies between short and sometimes are merged together or curved and their number decreased towards the tip; the posterior dentations can vary between absent or long and numerous and sometimes increased in their number towards the tip of the spine; the dorsal, anterior and ventral processes are well developed structures, with rounded, flange-like, and the shape of the basal fossa varies in having narrow, elongated, boat-shape, with high walls at sides; and very wide fossa and lunate in shape. It is usually deep with high walls.

Comprehensive Insight into Lake Nasser Environment: Water Quality and Biotic Communities—A Case Study before Operating the Renaissance Dam

This study focused on the monitoring and assessment of aquatic ecosystem functioning based on the abiotic and biotic features of Lake Nasser in the post-flood and pre-flood periods as the last ones before water storing behind the Grand Ethiopian Renaissance Dam. The physicochemical parameters, distribution and structure of biotic communities, including bacteria, phytoplankton, zooplankton, macrophytes, epiphytes and fish were analyzed at 15 sites. The values of most parameters (primarily temperature, total suspended solids, pH, orthophosphates, carbonates, sulphates and some cations) were higher in the pre-flood period, whereas higher values of conductivity, total dissolved solids, total solids, nitrites, nitrates, chemical oxygen demand, bicarbonates and chlorophyll a were recorded in the post-flood period. Cyanobacteria-dominated phytoplankton and total coliform bacteria were more abundant in the pre-flood period, and especially at sites 10–15, whereas higher abundances of zooplankton were recorded in the post-flood period. All these changes in parameters were significantly differentiated, and only the concentrations of dissolved oxygen, biochemical oxygen demand, ammonium and silicates were at similar level in both periods. The study also indicated that environmental factors had affected the macrophyte distribution and the adaptation of the invasive species Myriophyllum spicatum to thrive under different environmental factors in the lake. Besides, macrophytes provided the habitat to other aquatic organisms, especially epiphytes, and also helped maintaining the good water quality, nutrient cycling and stabilizing rivers’ and lakes’ banks. Generally, these conditions were rather favorable for biological processes and fish production.