In April 2005 up to September 2005, twelve earthen ponds in special fish farm at El-Tal El-kaber Ismaelia governorate were chosen and divided into four groups in a triplicate manner. Ismaelia canal water irrigates the first and second groups; however, the third and fourth groups were irrigated with agriculture drainage water. Oreochromis niloticus were distributed at a rate of (3 fish/m3), except for the second treatment where the culture was semi-intensive (12 fish/m3).The differences in water resources and type of fish culture affect the quality of water with a significant increase in ammonia. As well as copper concentrations in ponds irrigated with agricultural drainage water. Moreover, fish exposed to the stress factors (stock density in Ismaelia canal and agricultural drainage water) showed some clinical and pathological signs including fins and tail rot with rough scales, severe oedema, eye opacity (uni, lateral or bilateral opacity), Pale gills, severe enlarged liver, hemorrhagic foci on liver surface, sever enlargement of spleen in addition to high rate of mortalities. Furthermore, high fish stock density (12 fish / m3) and the usage of agricultural drainage water in fish culture elevate plasma cortisol level, lowering gamma globulin and consequently increased rate of fish infection with bacterial diseases.
Key words: Copper, bacterial infection, cortisol hormone, Oreochromis niloticus.