الفهرس 
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Abstract
The present investigation was designed to study the quality of 100 sampes comprised four species of fresh water fish namely T. niloticus, M. cephalus, B. bajad and C. lazera (25 of each) which were collected from commercial fish markets in Alexandria over a period of 6 months.
Sensory assessment as a mean of determinating quality showed that 88 out of 100 examined samples (88%) were accepted. Only one of each T.niloticus,M. cephalus and B.bajad was unaccepted. The accepted T. nilotica had 10 total score, M.cephalus had 12 total score , B. bajad had 10 total score and C. lazera had 3 total score from 15 total score.
Two chemical parameters namely pH and total volatile base nitrogen (TVBN) were used for determining fish quality. The mean pH values of the examined T. nilotica, M. cephalus, B. bajad and C. lazera were 6.4 ± 0.4, 6.3 ± 0.3, 6.6 ± 0.3 and 6.8 ± 0.5, respectively whereas the mean TVBN contents were 12.32 ± 1.6, 1.12 ±1.1, 15.6 ± 2.1 and 9.3 ± 1.2 mg/100g muscle of the examined fishes, respectively. A significant difference was noticed in the PH values and TVBN contents between the four examined fish species.
Regarding the microbiological status of the examined fish, the mean TBC values were 4.38 x 104 ± 3.2 x 103 , 6.6 x 103 ± 4.0 x 102, 1.4 x106 ± 3.3 x104 and 3.82 x104 ± 3.5 cfu/g of examined T.nilotica, M. cephalus, C.lazera and B. bajad, respectively .
There is a significant difference between the mean values of total mesophilic bacterial counts between species at P<0.01.
As for Enterobacteriaceae count the corresponding mean values were 3.04 x 103 ± 0.23 x 103, 3.67 x 103 ± 0.42 x 103, 2.4 x 104 ± 1.96 x 103 and 2.79 x 103 ± 0.19 x 103 cfu/g of examined T. nilotica, M. cephalus, C. lazera and B.bajad, respectively. Also There is a significant difference between the mean values of total Enterobacteriaceae counts between species at P<0.01.
As for Coliform count the mean values were 1.69 x 103 ± 0.15 x 103 , 1.98 x 103 ± 0.32 x 103, 1.4 x 104 ± 3.29 x103 and 1.44 x 103 ± 0.14 x 103 cfu/g of examined T. nilotica, M. cephalus, C.lazera and B.bajad, respectively. There is a significant difference between the mean values of Coliform counts between species at P<0.01.
Also for Staphylococcal count the mean values were 3.84 x 102 ± 0.46 x 102, 3.56 x 102 ± 0.41 x 102, 3.72 x 103 ± 3.89 x 103 and 4.4 x 102 ± 0.49 x 102 cfu/g of examined T.nilotica, M.cephalus, C.lazera and B. bajad, respectively. Also There is a significant difference between the mean values of total Staphylococcal counts between species at P<0.01.
Mycological evaluation of the examined fishes revealed that the mean yeast count values of T. nilotica, M. cephalus , C. lazera and B. bajad were1.34 x 103 ± 0.08 x 103, 1.52 x 103 ± 0.13 x103, 0.17 x 103 ± 0.03 x 103 and 0.52 x 103 ± 0.05 x 103 /g , respectively while that of the mould counts were 1.52 x 102 ± 0.14 x102, 1.52 x102 ± 0.13 x 102 , 0.2 x 102 ± 0.03 x102 and 2.12 x 102 ± 0.2 x 102 /g , respectively. Also there is a significant difference between the mean values of yeast and mould count cfu/g between species at P< 0.01.
The public health hazard of the obtained results as well as the recommended measures to improve the quality of fishes were discussed.