الفهرس 
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Abstract
Objectives: A field study during the summer season of 2013 was performed in two Hapas constructed in an earthen pond belonging to a private fish farm at Tolmpat 7 – Kafr El-Sheikh governorate to study the effects of feeding fish [in a polyculture system consists of four freshwater species, mainly Nile tilapia (T), silver carp (Sc), common carp (Cc), and African catfish (Cf) at a stocking rate 1: 1: 1: 1] the sewage (S) sludge comparing with a commercial diet for fish as a control (C) for 120 days.
Methods & Results: The first Hapa’s fish were fed the control diet and the fish of the second one were fed sewage sludge (product of treating sanitary and agricultural drainage of Al-Reiad belonging to Kafr El-Sheikh). The diet, sewage sludge and fish as well as rearing water were analyzed. Throughout the experimental period, any symptoms and death cases were recorded. At the end of the experiment, blood samples were withdrawn and liver samples were taken from the fishes for examination. from the results obtained, it was clear that sewage sludge contained very high percentage of ash and very low percentages of EE and total carbohydrate percentages comparing with the diet. Throughout the field experiment, mean values of some water parameters were 25±3 ºC for temperature, 8.80 pH, and 2.66 ppm for dissolved oxygen. Sewage sludge contains higher levels of P, Cu, Pb, and Cd than the commercial control diet. The P and Cd levels were higher in sewage sludge fed fish than the control fish, regardless of the fish species. However, catfish body contained the highest level of P and Cu but silver carp body contained the highest Pb and Cd levels. The interaction effect (dietary treatment X fish species) was significant, except for Cu. The control fish muscles presented higher contents of Cu, Pb, and Cd, but the opposite was true for P where the sewage sludge fed fish contained significantly higher level of P in their muscles than the control fish, silver carp contained significantly higher Cu and Cd and tilapia contain the highest level of Pb in the muscles comparing with the other fish species, regardless of the dietary treatment. Concerning survival rate, when the fish were fed the sewage sludge, silver and common carps were more tolerant than Nile tilapia and catfish. Sewage sludge feeding did not negatively affect the blood picture in general, although the significantly elevated values of transaminases activity and triglycerides concentration. Sewage sludge feeding led to some alterations in the liver structure.
Conclusively, and because of the presence of some pollutants from agricultural and urban drainages whether in the rearing water or in the sewage sludge that can negatively affect fish health, production, and quality as well as could be inter the food chain and threat human health; so, it is recommended to give more concern on food and water quality (environmental friendly) used in aquaculture to offer safe products for human consumption.