# Physiological and Intestinal Microbiota Analyses Offer Insights into the Analysis of Differential Residual Feed Intake in Jian Carp (Cyprinus carpio var. Jian)

## TL;DR

This study explores how Jian carp with better feed efficiency have healthier intestines and a beneficial gut microbiome, offering insights for sustainable aquaculture.

## Contribution

The study reveals that improved feed efficiency in Jian carp is driven by enhanced physiological health and a beneficial gut microbiome.

## Key findings

- Fish with lower residual feed intake (LRFI) had higher digestive and antioxidant enzyme activities and better intestinal health.
- The LRFI group had a gut microbiota enriched with taxa linked to beneficial metabolic functions.
- Improved feed efficiency is driven by a combination of physiological advantages and a favorable gut microbiome.

## Abstract

This study investigates the regulatory mechanisms of residual feed intake (RFI) in Jian carp (Cyprinus carpio var. Jian) from an integrated perspective, encompassing growth performance, physiological and biochemical parameters, and intestinal microbiota. We compared two groups of fish: HRFI and LRFI. We found that the more efficient fish did not grow faster or bigger, but they ate less feed to achieve the same size. Their advantage came from having healthier intestines with better structure and stronger digestive power, a more robust body-wide antioxidant defense system, and a different set of gut microbes linked to beneficial metabolic functions. Our results show that feed efficiency is a complex trait driven by the combined benefits of better internal health and a helpful gut microbiome, offering new insights for breeding and managing fish in sustainable aquaculture.

Feed efficiency (FE) is a critical economic trait in aquatic species. This study aimed to assess the effects of residual feed intake (RFI) divergence on growth performance, as well as antioxidant, digestive, and immune capacities. Additionally, intestinal microbiome was also employed to reveal the mechanism affecting the RFI in Jian carp. After the 8-week culture period, 12 fish (25 ± 1.05 g) each from the highest and lowest RFI extremes were selected as the HRFI and LRFI groups, respectively, for detailed physiological and microbial analysis. In terms of growth performance, the RFI, FCR, and DFI were found to be significantly lower in the LRFI group (p < 0.001), whereas no differences were observed in the ADG, BWG, SGR, HIS, VSI, and CF (p > 0.05). For physiological performance, the activities of digestive enzymes (protease, lipase and amylase) and antioxidant enzymes (T-AOC, SOD, CAT, GPx) were significantly higher in the LRFI group than in the HRFI group (p < 0.001). In line with this, the integrity of the intestinal tissue in the LRFI group was also superior to that in the HRFI group. Furthermore, the expressions of immune-related genes (LEP, GHR, AGPR, NPY) followed the same pattern. However, the expression of the CCK gene was significantly higher in the HRFI group (p < 0.001). There was no significant difference in the total lipid and fatty acids contents of muscle between the RFI groups (p > 0.05). Microbiota analysis indicated that the LRFI group harbored a higher relative abundance of several microbial taxa often associated with beneficial metabolic functions, including s Cetobacterium_sp_ZOR0034, unidentified_Chloroplast, Chloroplast, and Mangrovibacter. KEGG functional enrichment analysis indicated that the functions of these microbiota were primarily associated with metabolic processes. Collectively, these results demonstrate that improved feed efficiency in Jian carp is collaboratively driven by enhanced physiological status (digestion, antioxidant, immunity) and a beneficial shift in gut microbiota. This study provides an integrated perspective for understanding the regulatory mechanisms of RFI and offers potential microbiota-targeted strategies for feed efficiency improvement in aquaculture.