Influence of herbal extract blend supplementation on growth performance, liver and intestinal health, intestinal transcriptome, and resistance to Aeromonas veronii in Micropterus salmoides with optimized feeding intervals

Our prior study has demonstrated that daily dietary supplementation with 1.0 g·kg⁻¹ herbal extracts (HE, comprising Scutellaria baicalensis, Taraxacum mongolicum, Biancaea sappan and Pulsatilla chinensis extract = 3.0: 1.8: 3.0: 1.7 (w/w/w/w)) can induce structural damage to the intestine, consequently impairing the growth performance of Micropterus salmoides. In the current study, we firstly investigated the effect of dietary HE (1.0 g·kg⁻¹) on resistance against Aeromonas veronii in M. salmoides with different post-feeding intervals, and found the highest survival rate was noted in the HSR group, where fish fed HE every three days, lasting for 28 days (phase I). Subsequently, the growth-related indexes, liver and intestinal health, intestinal transcriptome of fish in the HSR group was assayed (phase II). The results revealed that the feeding pattern in the HSR group had no significant impact on hepatic and liver morphology. However, it notably enhanced the growth rate, reduced malondialdehyde content, and decreased the activity of aspartate aminotransferase and alanine aminotransferase. Additionally, 275 upregulated and 183 downregulated genes were observed between the HSR and control groups by transcriptome analysis. The KEGG analysis illuminated that differentially expressed genes were predominantly annotated in endocytosis, lysosome, and MAPK signaling pathway. Among them, the growth-related genes, including fibroblast growth factor receptor 4-like, insulin-like growth factor I, alpha-galactosidase A, and beta-galactosidase- 1-like protein 2 were considerably upregulated, while the immune related genes, such as interleukin-1 beta, dual-specificity phosphatase 1, and dual-specificity phosphatase 2 was significantly downregulated. These results collectively illustrated the feeding pattern in the HSR group might be a potential approach to combat against A. veronii, as well as to mitigate the negative effect induced by intake of high level of HE for M. salmoides.