Feeding on phytoplankton profile of two African Cichlids in large reservoir, Lake Nasser, Egypt

Abstract

This study was carried out in 2016 to investigate the feeding on phytoplankton profile of the Nile tilapia (Oreochromis niloticus) and mango tilapia (Sarotherodon galilaeus) inhabiting Lake Nasser, and its relation to their fisheries biological parameters. Phytoplankton Preference index (PPI), Index of Relative Importance (IRI), and Straus Linear index were used to investigate the feeding patterns of the two species in the lake. Moreover, some fish biological parameters of the two species were determined in the lake different areas. The results showed that O. niloticus and S. galilaeus feed mainly on the same phytoplankton items. Bacillariophyceae was identified as the most desired phytoplankton item to O. niloticus (IRI = 12.53) and S. galilaeus (IRI=18.28). Both fish species were more selective to five species from Bacillariophyceae and five species from Chlorophyceae, while they were more avoidant to four species from Cyanophyceae at all lake's areas. The results also showed that the main fisheries biological parameters are varied significantly between the two species and through lake different areas. This study concluded that the variation in fisheries biological parameters in Lake Nasser is not related to the pattern of feeding on phytoplankton but is led by other factors (e.g. fishing practices).

Food and feeding habits of Oreochromis niloticus (Linnaeus, 1757) in a tropical soda lake, lake Shaalaa, Ethiopia

“…This indicated that the fish was a phytoplanktivorous or herbivorous feeder. These findings are supported well by earlier findings that have classified O. niloticus as herbivorous that favor phytoplankton species [38,14,2,19] . Phytoplanktivorous or herbivorous feeding habits of O. niloticus have also been reported in Ethiopian water bodies such as Lake Chamo [38] , Koka Reservoir [14] and Lake Hayq [4] .…”

“…GIIi index treats each dietary metric equally and some prey items were better represented by %N (e.g., smaller but countable prey) whereas others were better represented by %V (e.g., fish and other larger prey). Phytoplankton preference index (PPI) was determined using percentage frequency of occurrence through the following equation described by Chrisafi et al [11] and Hussian et al [19] .…”

“…The different values of this index, allow separation of phytoplankton preference to three categories as main diet, secondary and accidentally eaten phytoplankton species [19] .…”

“…At the same time a number of piscivorous birds such as the Great White Pelican (Pelecanus onocrotalus roseus) and cormorant have been migrating to adjacent lakes. Studies on the diet composition and natural feeding of fish are important for the identification of the trophic relationships present in aquatic ecosystems, identifying feeding composition, structure and stability of food webs [34,19] . O. niloticus has a flexible feeding habits, characterized by generalist and opportunistic omnivorous feeding behavior [35,19] .…”

“…Studies on the diet composition and natural feeding of fish are important for the identification of the trophic relationships present in aquatic ecosystems, identifying feeding composition, structure and stability of food webs [34,19] . O. niloticus has a flexible feeding habits, characterized by generalist and opportunistic omnivorous feeding behavior [35,19] . Moreover, its food composition vary within a wide range of seasonal and spatial condition of the environments, maturity, size and age of the fish [38,14,12] .…”