## 1 Introduction  
Over the last decade, high-added-value seafood products, including smoked fish, gravlax and sea salads, have been gaining popularity in Europe and have dedicated refrigerated shelves in supermarkets. Cold-smoked salmon (CSS) is one of the best-selling products. The European production was estimated at 175,000 tons in 2019 for a trade value of 2.77 billion EUR, where the domestic demand mainly included France, the United Kingdom, Spain and Poland [1; 2]. The smoking process is one of the oldest methods used to preserve fish. The process consists of three steps, namely, salting (dry salt or brine), drying and smoking sensu stricto. The smoking temperature varies from 22-25 \({}^{\circ}\)C for CSS to 70 \({}^{\circ}\)C for hot-smoked salmon. The production of gravlax includes just the stages of salting, with a mixture of dried salt, sugar, spices and herbs, and drying. CSS and salmon gravlax (SG) are lightly processed products (NaCl < 6% in the water phase, pH > 5, phenolic compounds < 20 mg/kg for CSS) that are usually stored at refrigerated temperatures under vacuum packaging (VP). Although not a common practice, a modified atmosphere (MAP) is sometimes used to store such products. The light processing step does not eliminate microorganisms. Some of them can grow during storage, leading to the production of off-odors and flavors and a pasty texture. The sensory acceptability usually ranges between 2 to 4 weeks for gravlax and up to 6 weeks for CSS. It is generally admitted that the CSS initial microbiota is dominated by Gram-negative bacteria that are typically associated with fresh raw fish, such as _Photobacterium_, _Shewanella_, _Vibrio_ and _Yersinia_. During storage, Gram-positive bacteria, especially lactic acid bacteria (LAB), such as _Carnobacterium_ and _Lactobacillus_, become predominant with concentrations around \(10^{7}-10^{9}\) CFU/g. However, Enterobacteriaceae, _Photobacterium_ and _Brochothorax_ can also be present at sufficient levels to induce spoilage [3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13]. Although rarely quantified, yeasts are found throughout storage as subdominant microbiota (\(10^{4}\) CFU/g) [3]. In SG and trout gravlax, Enterobacteriaceae dominate the ecosystem but LAB and to a lesser extent _Brochothorax_ are also present [14; 15; 16]. Recently, new culture-independent methods, such as 165 rRNA gene Illumina metabarcoding or 4-5-4 pyrosequencing, were used to obtain a full and clear picture of the microbial ecosystem composition and dynamics in foods. To date, only three studies considered VP CSS and involved twenty-two batches from different smokehouses and salmon origins analyzed throughout the storage [17; 18; 19]. A core microbiota between samples could clearly be found, even if some variation was observed. The initial microbiota was generally dominated by _Photobacterium phosphoreum_/_kishitatini_, _Alivibrio_ sp., _Lactobacillus sakei_, _Brochothrix thermoplastica_ and, to a lesser extent, a few LAB, such as _Leuconostoc gasicmitatum_, _Lactococcus piscium_, _Carnobacterium divergens_ and _Carnobacterium malatromaticum_. The storage conditions exerted strong selective pressure on the initial microbiota and, at the spoiling date, the composition was highly variable between samples. Some batches were dominated by _Staphylococcus quorum_ and LAB (_Lactobacillus curvatus_, _Lactococcus lactis_, _C. divergens_, _C. malatromaticum_), while others were dominated by _B. thermosphacta_ and LAB (_C. malatromaticum_, _Lactobacillus fuchuensis_) or by _P. phosphoreum_/_kishitatini_ alone. Enterobacteriaceae (_Serratia proteamaculans_ and _Hafnia alvei_) were also detected in some samples, as well as _Psychrobacter_, _Shewanella_, _Salinivibrio_ and unexpected _Pantoea_ genera. No study was found on MAP CSS dices, and only one concerned a single batch of SG [16]. Its initial ecosystem was mainly composed of _Photobacterium_ and _Pseudomonas_ and many subdominant operational taxonomic units (OTU).