To investigate the effects of different raising environments on the flesh quality, the study set up three groups of silver carp (Hypophthalmichthys molitrix), that is, pond-farmed; short-term stocked; and ranched, grown in a natural water ranch. This study compared the differences in muscle proximate composition and amino acid composition among three groups. The results showed that there was no difference between the ranched and the stocked groups in content of crude protein, ash, total amino acids (TAA), essential amino acids (EAA), and umami-flavored amino acids (UAA), with both groups being significantly higher than the farmed group. This shows that, in terms of flesh quality, the stocked group was closer to the ranched group and better than the farmed group after being stocked in natural water for 30 days. The results suggest that the flesh quality of farmed fish was improved by short-term stocking in natural water. To elucidate the reasons of flesh quality change in the stocked group, this study compared the food composition and intestinal digestive enzyme activity in three groups, demonstrating that the ranched and stocked groups had similar food composition, with their detritus proportion lower than that of the farmed group, consuming easily digestible phytoplankton diatoms rich in amino acids and fatty acids. No significant difference was seen between the ranched group and the stocked group, for which amylase, lipase, and trypsin activities were lower than that of the farmed group. It is hypothesized that differences in environmental and food composition resulted in lower digestive enzyme activity in the ranched group and the stocked group. In summary, the short-term stocking of farmed fish in a natural water ranch can effectively improve the nutrient content, quality and flavor, and promote value of fish products.

Mandarin fish (Siniperca chuatsi) is a commercially important species in China. The number of pyloric caeca, essential for digestion and nutrient absorption, varies considerably (198–386) among individuals, but its relation to growth remains unclear. In this study, 300 samples from the first filial generation (F1) of farmed wild stocks were reared for 56 days and grouped based on pyloric caeca number. Fish with more pyloric caeca (≥289) exhibited significantly higher weight gain rates (WGRs), specific growth rates (SGRs), and digestive enzyme activities compared to those with fewer caeca (≤229). The final body weight (FBW) and the WGR showed moderately positive correlations with caeca number. These results showed that pyloric caeca number may be a valuable trait for selective breeding. To explore its genetic basis, a genome-wide association study (GWAS) identified over 1.4 million SNPs across 24 chromosomes. Twelve SNPs were potentially associated with pyloric caeca number, and we successfully identified one SNP that could effectively distinguish groups with the extreme number of pyloric caeca. Candidate genes near significant loci were enriched in pathways related to cell proliferation, differentiation, and metabolic regulation. These findings suggest a potential association between pyloric caeca number and growth, providing a possible reference for future molecular breeding in mandarin fish.

The characteristic of mandarin fish (Siniperca chuatsi) on live prey during the initial feeding stage poses challenges to artificial breeding and increases production costs. To evaluate the feasibility of replacing live prey and to investigate its effects on digestive function, 3 days post-hatch larvae were divided into two groups: a control group (HB) fed continuously with silver carp larvae, and an experimental group (AB) fed Artemia enriched with Schizochytrium from 3 to 6 days post-hatch, followed by silver carp larvae until 9 days post-hatch. Despite nutritional enrichment, the crude protein content of Artemia remained significantly lower than that of silver carp larvae. Growth performance was impaired in the AB group, with total length, specific growth rate (SGR), and survival rate (SR) all significantly reduced compared with the HB group. Except for pepsin, the activities of trypsin, lipase, and chitinase were significantly elevated in the AB group, indicating enhanced digestive stress. Histological examination revealed exfoliation and disorganization of the intestinal mucosa, shortened villi, and marked thickening of both intestinal walls and villi in the AB group. Transcriptomic analysis further demonstrated that differentially expressed genes in the AB group were enriched in immune- and apoptosis-related pathways, including IL-17, Toll-like receptor, TNF, NF-κB, and apoptosis signaling pathways. qPCR validation confirmed significant upregulation of key genes (il17ra1a, cxcl19, ccl20a.3, tnfb, casp7, casp10, and bax), aligning with transcriptomic trends. In conclusion, although nutrient-enriched Artemia may have short-term potential as an alternative initial diet, it can induce digestive stress and intestinal responses in mandarin fish larvae, thereby compromising growth and survival. This study provides useful references for optimizing feeding strategies at the initial stage and evaluating intestinal health in juvenile mandarin fish.