الفهرس 
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Abstract
A total of one hundred samples of raw fish (Oreochromis niloticusand Clarias lazera, 50, each) were randomly collected from different fish markets at Zagazig city, Sharkia Governorate. The samples were aseptically transferred in an ice box to Meat Hygiene Laboratory, Faculty of Veterinary Medicine, Zagazig University.
1. Organolepticexamination:
All the examined samples were considered fresh from organoleptic standpoint of view. The organoleptic evaluation of O. niloticussampleswas94.2%, while, it was 90.7% for C. lazera samples.
2. Chemical examinations:
2.1. Quality parameters:
2.1.1. Hydrogen ion concentration (pH):
The pH values varied from5.93 to 6.25 and 6.07 to 6.41, with mean values of 6.08±.033 and 6.23±0.037 in the examined Oreochromis niloticusand Clarias lazera, respectively. The differences between the two species were significant (p˂0.05).
2.1.2. Determination of thiobarbituric acid number (TBA):
The mean values of TBA (mg/kg)was1.63±0.203 and 2.29±0.285, with minimum values of 0.76 and 0.98 and maximum values of 2.59 and 3.63 mg/kg in the examined O. niloticusand C. lazerarespectively.The differences between the two species were non-significant (p>0.05).
2.1.3. Determination of total volatile nitrogen (TVN):
Total volatile nitrogen(mg%) ranged from3.84 to 21.57 and 5.22 to 28.09, with mean values of11.73±1.908 and 16.69±2.531 for O. niloticusand C. lazera.