Aims: The goal of this study was to monitor the quantitative and qualitative bacterial flora in the intestine of hybrid tilapia in fresh fish and fish kept in frozen storage conditions for 1 year.
Methods and Results: Quantitative and qualitative analyses of the bacterial flora associated with the intestine of hybrid tilapia (Oreochromis niloticus × Oreochromis aureus) in fresh fish and fish kept in frozen storage conditions for 1 year were carried out. In fresh and frozen fish, aerobic plate count (APC) ranged from 1·6 ± 1·2 × 108 to 1·5 ± 0·9 × 105 CFU g−1 in the intestine of tilapia collected from pond 1, 8·7 ± 2·3 × 107 to 6·5 ± 3·8 × 104 CFU g−1 in the intestine of tilapia from pond 2, and 1·9 ± 2·9 × 108 to 6·2 ± 2·8 × 104 CFU g−1 in the intestine of tilapia from pond 3. APC for all the groups of fish decreased c. 2-log cycles after 1 months frozen storage; thereafter, counts slowly declined during frozen storage for 1 year. Altogether, 16 bacterial genera were identified: Gram-negative rods (67%) dominated. Both in fresh and frozen conditions, four bacterial species viz. Shewanella putrefaciens, Corynebacterium urealyticum, Aeromonas hydrophila and Flavobacterium sp. were always present, with a prevalence of 10% in most cases. Shewanella putrefaciens was the most dominant organism (15% of the total isolates) throughout the studied period. During frozen storage some of the bacteria were not recovered, but most of the bacteria survived after prolonged freezing.
Conclusions: This study describes the aerobic heterotrophic microflora found in the intestine of fresh and frozen tilapia. The unique aspect of this study concerns the data revealing the micro-organisms, which are viable after prolonged freezing. Contamination of edible portions of fish could originate from gastrointestinal sources.
Significance and Impact of the Study: The present results may enhance knowledge in controlling the storage life of fish, and fish product quality. Bacterial activity is by far the most important factor influencing fish quality, so bacterial numbers can be used as an index of quality. Storage of frozen tilapia without evisceration could be avoided.