This study was conducted to investigate the effect of using thermally oxidized commercial frying oil instead of commercial frying oil as unusual energy source for Nile tilapia. The responses of Nile tilapia tested in this study were weight gain, feed conversion, dressing percentage, histopathological changes, mortality rate and food cost per k/g body gain were calculated. A total of 36 Nile tilapia were randomly distributed into 2 experimental groups and fed isocaloric and isonitrogenous diet containing commercial frying oil for the control groups and thermally treated commercial frying oil for 8 hours as experimental group. The frying performance and stability of commercial oil blended for at least 8 h. showed that: ( A ) oil oxidation hence reduction of unsaturated fatty acids, as indicated by change in the iodine value or number, ( B ) hydrolysis of oils ,as shown by changes in the FFA ( free fatty acids ) value, ( C ) blended oil exhibited visual increase in viscosity or turbidity and ( D ) changes in TBA concentration (thiobarbituric acid), as indicator of fat oxidation and rancidity. Thus, the thermal treatment of frying oil results showed a change in behavior and quality of the oil during blended. The thermally oxidized frying oil had specific effect on feed intake. Significant response of Nile tilapia to the use of heated fraying commercial oil was observed in body gain, feed conversion, and feed cost. Susceptibility of tissue to lipid per-oxidation was increased by feeding oxidized commercial frying oil especially hepatic and intestinal tissue.
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