Vietnamese Tra fish (Pangasius hypophthalmus) have become highly appreciated by consumers in the European Union, USA, Canada, etc. and are therefore of worldwide economic importance. However, the availability of data on the microbiological quality and safety of this fish species is limited. The dynamics of microbiological performance between large and small scale Vietnamese Pangasius processing plants (where non-chlorinated water and chlorinated water was used during the washing steps, respectively) were evaluated from the raw materials until final product by means of a microbial assessment scheme (MAS). A total of 279 samples (135 samples from the large scale plant) were taken to assess the overall microbial quality (psychrotrophic aerobic count), hygiene indicators (Escherichia coli and Staphylococcus aureus), and relevant pathogens (Listeria monocytogenes and Vibrio cholerae). Low levels of total psychrotrophic bacteria (ca. 3 log CFU/g) and E. coli (below quantification limit) were found on the final products sampled from the large scale plant. In addition, Listeria monocytogenes and Vibrio cholerae were absent in all the samples analysed. On the contrary, high numbers of psychrotrophic bacteria (ca. 6 log CFU/g on fish and ca. 6 log CFU/100 cm² on food contact surfaces) were found in the small scale plant during processing. Additionally, foodborne pathogens were present in the water, hands and fish; especially L. monocytogenes as a result of inadequate hygiene practices in the processing environment. These data are of major importance in order to provide valuable information for the local and international trade point of view in general and for the intended customers in particular.

Key words: Tra fish, Pangasius hypophthalmus, microbiological safety, microbiological quality