الفهرس 
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Abstract
A total of 210 cultured monosex Oreochromis niloticus of total length (23±5cm) and average body
weight (257±10g) were collected randomly from seven fish farms at the end of the production season
(November 2019) from farms in Ismailia and El-Sharkeya governorates. Water samples were taken monthly
with the detection of temperature, dissolved oxygen, pH, salinity, ammonia and nitrite levels along the
production season (from April to November). Then farms were divided into control, low ammonia and high
ammonia level groups. The main clinical picture in high ammonia level ponds were emaciation, sluggish
movement, surfacing, corneal opacity, slimy body with pale skin, hemorrhages all over the body, at fin
bases and on gills. Liver showed enlargement, paleness or congestion, gall bladder is engorged and/or
hemorrhagic. Kidney and spleen sometimes were congested. Serum total protein, albumin and globulin were
decreased by increasing water ammonia while albumin / globulin ratio showed no significant difference
between the 3 groups. Lysozyme activity showed an increase with the decrease of water ammonia
concentration. Antioxidant activity was recorded as CAT and SOD enzymes in liver and muscles and nitric
oxide in muscles revealed an inverse relationship with the increase of water ammonia while MDA showed
increased relationship. Also, ammonia levels in muscles decreased with the increase of water ammonia.
However, muscle nitrite levels showed insignificant difference among the 3 examined groups.