## 2 Results
### Biological, Gut Morphological and Physiological Responses in Different Reproductive Stages
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Item** & & **NRS** & **RS** & **PRS** \\ \hline \multirow{4}{*}{Mucous cell} & Type I & 1.27 \(\pm\) 0.21 \({}^{\text{a}}\) & 0.51 \(\pm\) 0.23 \({}^{\text{b}}\) & 1.16 \(\pm\) 0.31 \({}^{\text{a}}\) \\  & Type II & 0.89 \(\pm\) 0.14 \({}^{\text{b}}\) & 2.18 \(\pm\) 0.37 \({}^{\text{a}}\) & 0.61 \(\pm\) 0.11 \({}^{\text{c}}\) \\ \cline{1-1}  & Type III & 8.75 \(\pm\) 1.19 \({}^{\text{a}}\) & 2.02 \(\pm\) 0.34 \({}^{\text{c}}\) & 5.75 \(\pm\) 0.75 \({}^{\text{b}}\) \\ \cline{1-1}  & Type IV & 3.68 \(\pm\) 0.75 \({}^{\text{b}}\) & 5.82 \(\pm\) 1.05 \({}^{\text{a}}\) & 3.95 \(\pm\) 0.93 \({}^{\text{b}}\) \\ \cline{1-1}  & Total & 14.59 \(\pm\) 2.27 \({}^{\text{a}}\) & 10.53 \(\pm\) 1.94 \({}^{\text{b}}\) & 11.47 \(\pm\) 1.87 \({}^{\text{ab}}\) \\ \hline Mitochondria in intestinal epithelial cells & 5.71 \(\pm\) 1.07 \({}^{\text{a}}\) & 2.14 \(\pm\) 0.83 \({}^{\text{b}}\) & 6.92 \(\pm\) 1.32 \({}^{\text{a}}\) \\ \hline Eosinophilic granulocyte in intestinal submuc & 0.45 \(\pm\) 0.33 \({}^{\text{b}}\) & 3.86 \(\pm\) 0.93 \({}^{\text{a}}\) & 0.79 \(\pm\) 0.56 \({}^{\text{b}}\) \\ \hline \hline \end{tabular} Note: Values in the table are represented as Mean \(\pm\) SD of mucous cell number in 100 \(\upmu\)m \(\times\) 100 \(\upmu\)m; values in the table are represented as Mean \(\pm\) SD of mitochondria number in intestinal epithelial cells in 1 \(\upmu\)m \(\times\) 1 \(\upmu\)m; values in the table are represented as Mean \(\pm\) SD of eosinophilic granulocyte number in intestinal submuc in 10 \(\upmu\)m \(\times\) 10 \(\upmu\)m; the data with different superscripts in the same row are significantly different (a \(>\) b \(>\) c; \(p\) \(<\) 0.05).  
\end{table} 
Table 2: Morphometric measurements of intestinal tract of female _M. terminalis_ in the different groups. Figure 2: The digestive enzymes activities (**A–F**) and antioxidant capability (**G–I**) of intestinal tract of the black Amur bream in the different reproductive statuses (NRS. non-reproductive stage; RS. reproductive stage; PRS. post-reproductive stage); (**A**). Amylase (AMY); (**B**). Lipase (LIP); (**C**). Trypsin (TRY); (**D**). Maltase (MAL); (**E**). Alkaline Phosphatase (AP); (**F**). Leucine–alanine peptidase (LAP) (**G**). Catalase (CAT); (**H**). Superoxide dismutase (SOD); (**I**). Glutathione reductase (GR). Note: Values in the table are represented as Mean \(\pm\) SE, \(n\) = 8; \({}^{\text{\text{\text{\text{\text  
Gut Microbiota Diversity and Ecological Networks among the Non-Reproductive, Reproductive and Post-Reproductive Groups  
The gut microbiota of the three distinct reproductive groups exhibited significant variations. The gut bacteria of NRS and RS were mostly Proteobacteria at the phylum level, accounting for 44.2% and 68.1%, respectively. The gut bacteria of PRS were characterized by Fusobacteria (40.3%) and Firmicutes (30.9%) indicated clear differences (Figure 3A). The alpha diversity (Chao1) of the NRS and PRS groups was much higher than that of the RS group at the genus level (Figure 3B). In addition, we generated a PCoA analysis based on Bray-Curtis distance from the gut microbial communities (species level) that showed that the samples in the RS groups were obviously separated from the NRS and PRS groups (Adions: \(R^{2}=046;p=0.001\); Figure 3C). Figure 3: An overview of the data. (**A**) A bar graph illustrating the comparative abundance of various phyla within the dominant phylum across distinct categories of fish guts. Only those with a mean relative abundance exceeding 1% within the phylum are displayed. “Unclassified” designations were applied to sequences that could not be assigned to a phylum. (**B**) Alpha diversity results of the gut microbial community for three groups distributed in the various reproductive statuses of _M. terminalis_ are presented; * \(p<0.05\), ** \(p<0.01\), and *** \(p<0.001\) denote statistical significance, respectively. (**C**) The PCoA ordination and adonis test in the _M.