Ecologically modified pond management improves flesh quality and gut microbiota of grass carp (Ctenopharyngodon idella)

In recent years, many earthen ponds in China have been modified into ecological engineering ponds to reduce pollution. This study aimed to assess the effects of modified pond management on the flesh quality and gut microbiota of grass carp (Ctenopharyngodon idella). To achieve this, grass carp were distributed into two groups: an earthen pond (group A) and a modified pond (group B), with all conditions kept the same. After 4 months of rearing, samples were collected for analysis. The results showed significantly reduced concentrations of total nitrogen (TN) and total phosphorus (TP) in the water from the modified pond. While no significant differences were observed in weight gain and muscle proximate composition, flesh quality was improved in the modified pond group, as evidence by lower pH and reduced cooking loss, increased hardness and springiness, and higher levels of saturated fatty acids (SFAs) and oleic acid (OA) in the dorsal muscle. In addition, gut morphology analysis showed increased villi height and more goblet cells. The gut microbial communities of grass carp from the modified pond exhibited higher richness, diversity, and evenness. Firmicutes became the dominant phylum, replacing Fusobacteriota, and the abundance of beneficial bacteria, such as Acidobacteriota, Actinobacteriota, and Cetobacterium, was higher, while harmful bacteria, such as Erysipelatoclostridium, showed reduced abundance. Pathogenic bacterium, such as Eschetichia-Shigella, Streptococcus, and Aeromonas, were only found in the earthen pond group. These findings indicate that modified pond management positively affects both flesh quality and gut microbiota, enhancing the overall health and performance of grass carp.