الفهرس 
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Abstract
Fish is the best animal protein due to its high Nutritive value as well as its high quality. Also, fish is rich in calcium, phosphorous, Iodine, Omega3, Omega6 and generous supply of B-complex vitamins as well as its lower content of cholesterol. Fish flesh is generally sterile immediately after catching; however, it may become contaminated with different microorganisms during subsequent handling as these microorganisms can penetrate from skin and the gut to the flesh for example salmonellae act as a public health hazard if present where it causes food poisoning. Also, Enteropathogenic E. coli may give rise to severe diarrhea in infants and young children as well as food poisoning and gastroenteritis among adult consumers.
This study was carried-out for, quality assurance of fresh water fish in Alexandria Province by using chemical and bacteriological examination of fish samples. A total of 150 random samples of fresh water fish, fishes represented by Tilapia nilotica, Mugil cephalus and Clarius lazera (50 of each) were collected from different Markets in Alexandria Province. The samples were placed separately in clean sterile plastic bags and transferred in an insulated ice box to the laboratory under complete aseptic conditions without any delay. All collected samples were subjected to bacteriological and Spoilage markers examination after thawing.
The obtained results revealed that:
A-Spoilage markers:
1. The pH values of Tilapia nilotica mean value was 6.29±0.06 (not exceed 6.5) according to ”EOS” (2005). The pH values of Mugil cephalus mean value was 6.20±0.04. pH values of Cat fish (Clarius lazera) mean value was 6.39±0.03.
2. The TVB-N (mg/100gm) value of Tilapia nilotica mean value was 10.62±0.27 (mg/100gm) (Not exceed 25mg/100gm) according to ”EOS” (2005). TVB-N (mg/100gm) value of Mugil cephalus mean value was 8.76± 0.31 (mg/100gm) and all samples within permissible limit (Not exceed 25mg/100gm). The mean value of Clarius lazera was 17.51±0.29 (mg/100gm) and all samples within permissible limit (Not exceed 25mg/100gm).
3. The Trimethyl amine (TMA) (mg/100gm) value of Tilapia nilotica mean value was 4.53±0.38 (Not exceed 10mg/100gm) according to according to ”EOS” (2005). Mean value of Mugil cephalus was 3.59± 0.22 (mg/100gm) and all samples within permissible limit (Not exceed 10mg/100gm). While in Clarius lazera was 4.86±0.15 (mg/100gm) and all samples within permissible limit (Not exceed 10mg/100gm).
4. The Thiobarbituric acid (TBA) TBA (mg/kg flesh of fish) mean value of Tilapia nilotica 1.18±0.19 mg/kg flesh and all samples within permissible limits (not exceed 4.5 mg/kg) according to according to ”EOS” (2005). Mugil cephalus was 1.82±0.14 mg/kg flesh and all samples within permissible limits (not exceed 4.5 mg/kg). While, in Clarius lazera was 2.21±0.13 mg/kg flesh and all samples within permissible limits (not exceed 4.5 mg/kg).
5. The free fatty acids (FFA) in examined different species of fish mean value for 0.31±0.02 mg% Tilapia; 0.14±0.35mg% for Mugil cephalus and 0.38±0.01mg% for Clarius lazera, respectively.
B- Microbiological evaluation
1. The Aerobic bacterial count (cfu/g) mean was 8.4x105±7.2x104 for Tilapia nilotica, 4.6x106±9.2x105 for Mugil cephalus, 3.6x106±8.24x105 for Clarius lazera. The ratio of samples above permissible limits (Not exceed 106 cfu/g, acc. to ES, 2005) were 42,46 and 44% in Tilapia nilotica, Mugil cephalus and Clarius lazera, respectively.
2. The Enterobacteriaceae count (cfu/g) mean was 2.1x105±0.81x105 for Tilapia nilotica, 6.7x105±1.7x105 (cfu/g) for Mugil cephalus and 6.8x105±1.4x105 for Clarius lazera. All examined samples were positive.
3. The Coliforms count (cfu/g) mean was 7.4x104±3.2x104(cfu/g) for Tilapia nilotica, 2.7x105±5.6x104 for Mugil cephalus, and 1.9x105±4.3x104 for Clarius lazera. All samples were positive and all were above permissible limits (should not exceed 102 cfu/g) ES, 2005.
4. The Incidence of E. coli was 38% in Tilapia nilotica and 28% in Mugil cephalus and 42% for Clarius lazera.
5. The frequency distribution of isolated E. coli in examined samples of Tilapia nilotica, Mugil cephalus and Clarius lazera samples was recorded as O26 (EPEC) (8,6 and 10%, respectively); O86(EHEC) (4,8 and 8%, respectively); O119 (EPEC) (8,6 and 12%, respectively); O126 (EIEC) (12,4 and 8%, respectively) and O124 (ETEC) (6,4 and 4%, respectively).
6. The incidence of Salmonellae in Tilapia nilotica were (4) with a percentage (8%) while, in Mugil cephalus were (6) with a percentage (12%). However, in Clarius lazera were (5) with a percentage (10%).
7. The incidence of S. Enteritidis in Tilapia nilotica, Mugil cephalus and Clarius lazera recorded as (4,2 and 2%; respectively); S. Typhimurium (2,6 and 4%; respectively). While, S. Haifa recorded as (2,4 and 4%; respectively).
8. Staphylococcus aureus count (cfu/g) of Tilapia nilotica mean was 9.2x102±2.6x102 (cfu/g) in 50 (100%) of examined samples. Mugil cephalus mean was 1.5x103±7.4x102 (cfu/g) in 50 (100%) of examined samples. While, Clarius lazera mean value was 8.9x102±5.4x102 in 50 (100%) of examined samples.
9. The Mould count (cfu/g) mean was 3.8x102±9x10 for Tilapia nilotica, 7.2x102±2.1x102 for Mugil cephalus, and 6.6x102±1.9x102 for Clarius lazera. All samples were positive.
10. The Yeast count (cfu/g) mean was 11.9x103±1.3x102 for Tilapia nilotica, 8.9x103±1.9x102 for Mugil cephalus, and 8.9x103±2.1x102 for Clarius lazera. All samples were positive.
The public health significance of contaminants and the possible sources of contamination of imported fish in these markets with these organisms as well as suggestive hygienic measures to improve the quality of such fishes were discussed.