ABSTRACThe present investigation aimed to study species composition, condition factor, growth and feeding habits of Orechromis niloticus (Linnaeus, 1758), Orechromis aureus (Steindachner, 1864), Tilapia zillii (Gervais, 1848) and Sarotherdon galilaeus (Linnaeus, 1758) in Abu-Zaabal Lakes, Egypt. The abundance of different species was seasonally fluctuated. It was found that O. aureus is the most common species constituting about 50.0%, followed by S. galilaeus, while O. niloticus ranked as the 3 rd species in the total catch. The highest value of the exponent "b" of length-weight relationship and condition factor "K" was recorded for T. zillii and the lowest for O. aureus. The valve of (K) was inversely related to the size of O. aureus and O. niloticus, and tends to be fairly constant in T. zillii and S. galilaeus. All cichlid species attained their highest growth rates in length during the first year of life, after which a gradual decline was noticed with further increase in age. O. niloticus had the highest growth rate than the other three species. The parameters of Von Bertalanffy growth model were estimated as L ∞ = 34. 59, 45.23, 39.88 and 30.65
This study has been carried out along the River Nile (river main stream, Rosetta and Damietta branches) in Egypt. Fish Samples of 21 species belonging to 11 families were collected mainly from the catch of three fishing gears and methods, Trammel net, Traps, and Long
ABSTRACThe present study is concerned with the seasonal analysis of the stomach contents of three species of cichlid fishes inhabiting Damietta branch of the River Nile, Egypt, namely Oreochromis niloticus (Linn., 1758), Sarotherodon galilaeus (Linn., 1758) and Tilapia zillii (Gerv., 1848). The natural food was studied from the stomach contents of fish ranging from 12-29, 11-24 and 10-21 cm in total length of the previous species, respectively. Stomach contents were analyzed using the frequency of occurrence and Percentage of composition methods. Additionally, feeding intensity, index of relative importance (IRI) and selectivity index (S) were calculated. The results showed that, food from plant origin dominates the diet of the three studied species and occurred frequently in more than 60.0% of the examined stomach. Values of IRI emphasized the importance of diatoms, blue green and green algae as major food resources in the stomach of O. niloticus followed by rotifers and organic detritus. S. galilaeus and T. zillii followed nearly the same trend as O. niloticus, but plant tissues follow blue green and green algae in the diet of T. zillii. IRI indicates also the importance of food of animal origin in the diets of O. niloticus and S. galilaeus than T. zillii. The feeding intensity is strongly influenced by season, since the highest stomach fullness occurred during summer. In conclusion, Cichlid fish species in Damietta Branch of River Nile are omnivorous, and did not consume food at random but have the ability to select and choose the preferred food stuff even during different seasons. These seasonal variations in preferred food makes the intraspecific competition between these species very low.
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