There are numerous factors that can have an impact on the microbial ecology and quality of frozen Pangasius hypophthalmus fillets during processing in Vietnam. The presence of spoilage bacteria along the processing line  can shorten the shelf-life of thawed frozenfish products. Therefore, the spoilage microbiota throughout the processing chain of two companies (BC: large scale factory, chlorine-based process, BW: large scale factory, waterbased process and SC: small scale factory, chlorine-based process) was identified by culture-dependent techniques and 16S rRNA gene sequencing. The microbiological counts were observed to be insignificantly different (p>0.05) between BC and BW. Surprisingly, chlorine treatedfillets from the SC line were revealed to have significantly higher microbial counts than potable water treatedfillets at BW line. This was determined to be a result of temperature abuse during processing at SC, with temperatures even greater than 10 °C being recorded from skinning onwards. On the contrary, the microbiota related to spoilage for BC and BW lines was determined by 16S rRNA gene sequencing to be more diverse than that on the SC line. A total of 174 isolates, 20 genera and 38 species were identified along the processing chains. The generaAeromonas, Acinetobacter, Lactococcusand Enterococcuswere prevalent at various processing steps on all the processing lines evaluated. A diverse range of
isolates belonging to the Enterobacteriaceaesuch asProvidencia, Shigella, Klebsiella,  Enterobacter, and Wautersiella were isolated fromfillets sampled on the SC line whereas Serratiawas only observed onfillets sampled on the BC and BW lines. The results can be used to improve Good Manufacturing Practices for processedPangasius fillets and to select effective measures to prolong the shelf-life of thawed VietnamesePangasiusfillets products

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