## 4 Discussion  
Through sensory evaluation, color, tvb-n, tca-soluble peptide, muscle glucose, lactate, total sugar, BAs, VOCs and microbial analysis, including the combination of high-throughput sequencing and SPME-GC-MS technology, the quality, bacterial community and composition of VOCs were explored, and the microbial spoilage of samples stored at 4 \({}^{\circ}\)C was studied. The correlation between microbiome and protein, carbohydrates and VOCs and its relationship with the sensory acceptability score enable us to understand how the quality of fish deteriorates during storage and how it is eventually rejected. This study clarified that the sensory acceptability of fish was unacceptable at day 8. The fish turnedj green and yellow. Protein degraded drastically after the 7 th day. Specifically, there was a sharp increase in the content of TVB-N and TCA-soluble peptides. The main use of microorganisms in fish in the early storage period may be glucose, and in the later period, it is mainly lactic acid. This is because the total sugar of samples decreased with the increase of storage time. In particular, the glucose content decreased rapidly in the early stage and then slowed down. However, the change of lactic acid is just the opposite. A total of 8 types of BAs can be detected in fresh fish. The content of spermidine and spermine are relatively high. When the fish has deteriorated on the 8 th day, tyramine, cadaverine and putrescine become the main BAs. The study studied diversity and succession of microbial communities during fish storage. The main bacteria produced during storage were Proteobacteria and Firmicutes, and the main bacteria were _Pseudomonas_, which was predictable. Previous studies have shown that _Pseudomonas_ and H\({}_{2}\)S producing bacteria are usually the cause of the quality loss of aquatic products [47; 48; 49; 50]. _Pseudomonas_ is the main spoilage microorganism of aquatic products under aerobic conditions [51] and has a strong ability to decompose protein and fat, resulting in the release of bad smell from fish, which is ultimately unacceptable to the senses [52]. In this study, at the end of storage at 4 \({}^{\circ}\)C, in addition to _Pseudomonas_, the microbiota present also included _Vagococcus_, _Acinetobacter_, _Brochothrix_, _Myroides_ and _Shevanella_, and the microorganisms such as _Vagococcus_, _Acinetobacter_ and _Myroides_ detected  
Figure 7: Correlation analysis of microbial species and VOCs in samples. at the beginning of storage were usually related to pretreatment. These pollution sources may come from workers, processing equipment, air, water, etc. [53; 54; 55]. Other bacteria from human and environmental sources, such as _Enterobacter_, _Enterococcus_, _Escherichia coli_, _Klebsiella_, _Shigella_ and _Staphylococcus_, were also commonly produced during capturing, processing and freezing, affecting the quality and safety of fish. The relative abundance of these genera was low in this paper, but that does not minimize the possibility of the existence of pathogens. They all contain human pathogens, which may be found in raw fish whether they are foodborne or not. In this case, eating undercooked fish may lead to food-borne infections. _Brochottrix_ and _Shewanella_ were not detected at the initial stage, but the relative content reached 5.57% and 0.42% at the end. _Brochottrix_ is a common spoilage bacterium in meat [56]. _Shewanella_ is a gram-negative psychrophilic bacterium, which can produce H\({}_{2}\)S, has the ability to reduce oxidized trimethylamine to trimethylamine and produce a variety of biogenic amines, and is the main potential spoilage microorganism of protein-rich aquatic products [57; 58]. It was found that during storage, _Planifilum_, _Mycobacterium_, _Thuera_ and many unknown bacteria decreased and were gradually replaced by _Pseudomonas_. In our study, the content of ethanol and ethyl acetate was high.