الفهرس 
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Abstract
The present study was undertaken to detect the prevalence of mycotoxins in fish feeds and assessment of its effect on fish health and growth. The mycological examination of samples of fish feeds revealed that the recovered genera of moulds were Penicillium spp., Aspergillus (flavus, niger) and Mucor Spp.The most predominant isolates were Aspergillus flavus that isolated from 40 out of 50 samples with a percentage of 80%, followed by Penicillium spp in 30 out of 50 samples with a percentage of 60%, Aspergillus niger recovered from 20 out of 50 samples with a percentage of 40%, and Mucor spp that obtained from 10 out of 50 samples with a percentage of 20%.
The aflatoxin B1 and ochratoxin A were measured in the five ration samples by Fluorometeric method and the result detected that the highest concentration of ochratoxin A was found in fourth sample at the level of 38 PPb, while the highest concentration of Aflatoxin B1 was found in the second sample at the level of 13PPb. Whereas, the lowest concentration of ochratoxin A was detected in second sample at the level of 7.6 PPb . While, the lowest concentration of Aflatoxin B1 was observed in the third sample at the level of 5 PPb. The total concentrations of aflatoxin B1 was ranged from 5 to 13 PPb and concentrations of ochratoxins A ranged from 7.6 to 38 PPb. The effects of experimental feeding of ochratoxins and aflatoxins contaminated ration on Tilapia niloticus was undertaken. The diminished body weight gain in fish fed on ration contaminated with AFs and OA was significantly improved after addition of yeast to the mycotoxicated feed. Whereas, the mortalities rate which observed in the mycotoxicated fish group were completely absent by adding yeast to the toxicated group. On the other hand, the hepatosomatic index calculated in the present experiment were increased after administration of yeast to fish with the mycotoxicated feed. Currently, no aflatoxins and ochratoxins residues levels in flesh of Tilapia niloticus were detected at the end of experimental period . The histopathological examination of liver and kidney tissues of fish in treated groups was carried out. The addition of yeast to the mycotoxicated feed to fish , increased the intracellular GSH and restore its levels following depletion through elevation in the glutathione peroxidase and glutathione reductase activities, total glutathione, and total reactive antioxidant potential levels . This beneficial effect of yeast was detected as a marked improvement of hepatic features manifested by mitigation of the vacuolar degenerative changes at both low and high doses and nuclear membrane integrity.