الفهرس 
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Abstract
The present investigation was designed to study the quality of 75 samples comprised three species of freshwater fish namely O. niloticus, C. gariepinus and B. bajad (each 25 ) which were collected from commercial
fish markets in Assiut over a period of 6 months .
Sensory assessment as a mean of determining quality showed that 73 out of 75 examined samples (97. 3 0/0) were accepted. Only two, one each from . C. gariepinus and B. bajad, were unaccepted . The accepted fishes were graded as class E ( 2 .7 0/0), class A (48 0/0) and class B ( 46 .6 % ) were graded E was considered very fresh while grade B was considered fish in the lowest sate of freshness . Non significant difference in the sensory scores could
be detected between the three species .
Two chemical parameters namely pH and total volatile base nitrogen ( TVBN ) were used for determining fish quality. The mean pH values of the examined O. niloticus , C. gariepinus and B. bajad were 6 . 64 ± 0.06 ,6 .96 ± o . 06 and 7 . 05 ± 0 . 03 , respectively whereas the mean TVBN contents were 11 .71 ± 1.2 ,6 .78 ± 1 .2 and 6 .38 ± Q . 71 mg 1100 g muscle of the examined fishes , respectively. A highly significant difference was noticed in the pH values and TVBN contents between the three examined fish species .
Regarding the microbiological status of the examined fishes, the mean APC values were 3 .4 ± 1. 6 x 106 , 3 . 5 ± 1. 3 x 106 and 6 ± 1 . 9 x 106 CFU Ig while that of the anaerobic count were 4 . 5 ± 3 .9 X 103 , 1 .3 ± 0 . 8 x 103 and 7 . 5 ± 2 . 4 x 102 CFU 1 g of the examined O. niloticus , C. gariepinus
and B. bajad, respectively. As for Enterobacteriaceae count the corresponding values were 7.5 ± 4.8 x 104,2.3 ± 1 .4 X 103 and 2 . 8 ± 0 . 9 X 103 CFU / g whereas the mean Aeromonas spp. counts were 1 .1 ± 1 . 0 x 106 , 1 . 3 ± 0 . 46 X 106 and 6 ± 2 .5 X 106 CFU / g ., respectively.
Correlation between the microbiological load and fish species results in non significant differences III the mean APC, anaerobic count, Enterobacteriaceae count and Aeromonas spp. count between the three examined fish species .
Members of Enterobacteriaceae recovered from the examined fishes were Citrobacter diversus ( 20 %) , Enterobacter cloacae (2 .7 %) , E. coli ( 16 % ) , Klebsiella oxytoca ( 12 %), K. peumoniae ( 8 % ) , Morganella morganii ( 2 .7 % ) , Providenica spp. (22 . 7 %) , Salmonella spp. ( 4 %) , Serratia spp . ( 17 . 3 %) and Shigella sonnei ( 2 . 7 % ) .
Furthermore the identified Aeromnas spp. which were recovered from the examined fishes were A . caviae , A . hyDROPhila and A . sobria . Their incidence was 14 .77 , 9 .3 and 60 % , respectively.
Mycological evaluation of the examined fishes revealed that the mean yeast count values of 0 . niloticus , C . gariepinus and B . bajad were 2 .1 ± 1 .1 x 104, 9. 4 ± 9 . 2 x 104 and 4 . 3 ± 2 . 3 x 104 / g , respectively while that of the mould counts were 4 . 3 ± 1 . 2 x 104 , 5 ± 4 x 103 and 1 . 7 ± 0 . 7 ± 103 / g , respectively. However, the overall mean values of total yeast and mould counts of the aforementioned fishes were 5.5 ± 1.9 x 104 , 9.9 ± 9.2 x 104 and 4.5 ± 2.2 x 104 / g respectively.
Correlation between the yeast , mould and total yeast and mould counts and fish species showed that a highly significant differences was observed in the mean mould count between O. niloticus and B. bajad only.
Fifteen mould speCIes belonging to 9 genera were recovered from the examined fishes in variant percentages . The identified fungal strains were Acremonium strictum , Alternaria alternata , Aspergillus flavus, A. fumigatus , A. niger , A. sydawii , A. versicolor , Cladosporium spp. , Eurotium halophilicum Fusarium spp. Geotrichum candidum , Penicillium chrysogenum , P. funculosum and Rhizopus spp.
The public health significance of the isolated microorganisms were discussed and the suggestive measures to protect the consumer and produce high quality fish were outlined.