## 3 Results and Discussion
### 16S rRNA High-Throughput Sequencing Analysis  
The 16S rRNA V3-V4 regions were sequenced on the Illumina HiSeq2500 platform, and the results are shown in Table 1. A total of 557,980 effective tags were generated from five samples, with an average of 111,596 tags per sample (range = 57,660-150,114, SD = 40,224). These sequences were grouped into 64,515 operational taxonomic units (OTUs) and assigned into 209 classified bacterial genera. The Shannon index and Simpson index of fresh fish fillets were 7.32 and 0.96, respectively, which were the highest among all fish samples (Table 1). The highest diversity indices indicated that the bacterial diversity was most abundant in the fresh fish fillets; this was also manifested in the relative abundance of the bacterial phyla and genera (Figure 4). Compared with fresh fish fillets, the Shannon index and Simpson index of the control samples decreased to 6.03 and 0.80, respectively, on day 3 (C3) of cold storage. The diversity index of the control samples on day 6 (C6) was similar to that on C3 (Table 1). The Shannon index and Simpson index of tea polyphenol-treated fillets reduced sharply to 3.05 and 0.40 on day 12 (TP12), respectively, but decreased slightly to 6.80 and 0.93 on day 6 (TP6), respectively. The reason for the decrease in the diversity of the control and treated samples could be due to the fact that some species of bacteria gradually adapt to the environment and become dominant during microbial growth responsible for spoilage. The results of the taxonomic assignment confirmed our hypothesis, with _Aeromonas_ accounting for 50.1% in C3 samples and _Pseudomonas_ accounting for 50.4% and 97% in C6 and TP12 samples, respectively (Figure 4). Diversity indices indicated that the bacterial diversity decreased as crisp grass carp spoiled;  
Figure 2: Changes in total volatile basic nitrogen (TVB-N) of crisp grass carp fillets during storage at 4 \({}^{\circ}\)C. \(\blacksquare\), distilled water treatments; \(\bullet\), tea polyphenol treatments. similar findings were reported earlier [7,12]. The higher diversity of TP6 samples than of C6 samples implied that tea polyphenol treatments delayed the growth of the dominant bacteria. This speculation was supported by the TVC results (Figure 1) and the abundance of the bacterial genera that accounted for not more than 21% (Figure 4). Principal coordinate analysis of the bacterial communities was performed to evaluate the similarities in the bacterial communities during cold storage. Both the weighted (Figure 3a) and unweighted (Figure 3b) samples revealed that the bacterial communities of the fresh fish (D0) were significantly different from those of the spoiled fish (C6 and TP12) (\(p<0.05\)), and these observations were in line with previous studies [7,12]. The bacterial communities in samples treated with the tea polyphenol and distilled water changed significantly during the storage period (TP6 and TP12, C3 and C6, \(p<0.05\)). However, the microbiome composition was strikingly similar between C3 and T6 (also C6 and T12), which implied delayed spoilage of fish treated with tea polyphenols. These findings were further confirmed by the results of the relative abundance of the bacterial genus (Figure 4b), which showed that the bacterial population were similar in composition but different in proportion.