الفهرس 
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Abstract
the present work was planned to investigate the effect of two major environmental stress factors effects on immune system of Tilapia niotica through some selected blood constituents and histopathological changes in T. niotica.
A total of 390 apparently healthy L niotica with body weight 13.5 and 23.5 gm/fish were used in two experiments (1 and 2), respectively. Experiment 1 was planned to study the effect of different levels of stocking densities 10, 30 and 40 fish! 100 L water while experiment 2 was to study the effect of 70 mg and 140 mg ammonium chloride! 100 L water on the immune syste4of fish compared to zero level of ammonium chloride. The following points were the main findings:
1. After 4 weeks of exposure to the stress factor. Serum
agglutinating antibody responses in fish kept at high stocking
densities (30 and 40 fish/100L) showed low antibody titers of 64
and 32 compared to fish kept in low stocking densities (10
fish/100L) responded strongly and gave agglutinating antibody
titer of 512.
2. The agglutinating antibody titers against hyDROPhila were clearly affected by exposing the fish to ammonium chloride.