This study investigated the effects of four flavonoids on growth and flesh quality of grass carp (Ctenopharyngodon idellus). Five diets were designed with the supplementation of quercetin (QC), rutin (RT), baicalein (BC) and catechin (CC) in basal diet (control) and were fed to grass carp (59.7 ± 0.2 g) for 60 days. The fish fed QC and RT diets, rather than BC and CC diets, showed higher weight gain (+4.0%, +3.9%) and lower feed conversion ratio (−0.07, −0.06) than the control fish. The contents of total collagen, heat-soluble collagen, total free amino acids and flavour amino acids in flesh were significantly increased by the supplementation of QC and RT in diets. The SOD activity and the contents of C22:5, C22:6 and n-3 PUFA were significantly increased, and the malondialdehyde and protein carbonyl contents were significantly decreased in the QC, RT and CC groups. In the metabolomics profiling of muscle, 102 and 68 named differential metabolites were identified in the QC and RT groups, and these metabolites were found to be involved in the pathways of “lipid metabolism” and “amino acid metabolism.” In addition, the mRNA expressions of IGF-1, PI3K, AKT and FAS in flesh were significantly up-regulated in QC and RT groups. In summary, dietary QC and RT promoted the growth and flesh quality of grass carp which might be associated with IGF-1/TOR, Nrf2, TGF-β/Smad4 and PPAR signalling pathway.

The present study aimed to systematically investigate the underlying differences in flesh quality between wild and farmed Monopterus albus. Fifteen healthy M. albus per group with an average body weight of 45 g were sampled to analyze muscle parameters by biochemical indicators, histomorphology, and molecular biology. Compared with the wild fish, the farmed M. albus in flesh had lower crude protein, collagen, lysine, histidine, total amino acids, SFA, n-3 PUFA contents, and n-3/n-6 ratio (p < 0.05), and higher moisture, crude lipid, crude ash, MUFA, n-6PUFA, and total PUFA contents (p < 0.05). The thawing loss, drip loss, steaming loss, and boiling loss in the farmed group were significantly higher, and hardness, springiness, cohesiveness, gumminess, chewiness, and resilience were significantly lower than those in the wild group (p < 0.05). In addition, higher muscle fiber density and lower muscle fiber diameter were observed in wild M. albus (p < 0.05). In muscle transcriptome profiling, differentially expressed genes and enriched pathways are primarily associated with muscle development, protein synthesis, catabolism, lipid metabolism, and immunity. To the best of our knowledge, this is the first investigation that compares the flesh quality between wild and farmed M. albus in terms of biochemistry, histology, and molecular biology levels. Overall, wild M. albus had a higher nutritional value and texture quality than farmed M. albus.

To investigate the effects of dietary tributyrin (TB) on grass carp (Ctenopharyngodon idella), five diets were prepared with supplementing TB at 0 (TB-0), 200 (TB-200), 400 (TB-400), 600 (TB-600) and 800 (TB-800) mg/kg and then fed to grass carp with initial body weight of 17.0 ± 0.2 g for 60 days. TB-400 and TB-600 groups presented higher weight gain, higher retention of protein, lipid, ash and lower feed conversion ratio than TB-0 group (p < .05), and TB-400 group also showed higher digestibility of dry matter and protein as well as intestinal amylase activity than TB-0 group (p < .05). Compared with the control, the serum superoxide dismutase activity was increased, and malondialdehyde content was decreased in TB-400 and TB-600 groups (p < .05), while TB-200 and TB-400 groups presented higher serum lysozyme activity than TB-0 group (p < .05). The villus height in foregut was increased in all the tributyrin-supplemented groups, but the villus height in midgut was increased only in TB-400 and T-600 groups (p < .05). The relative abundance of Erysipelatoclostridium tended to increase, and Aeromonas tended to decrease in TB-400 group. In conclusion, dietary tributyrin promoted the growth and feed utilization, enhanced serum antioxidant capacity and improved intestinal health of grass carp. Based on growth performance, the appropriate dietary supplementation of tributyrin is 443.5 mg/kg by using quadratic regression analysis.

As consumer demand for quality fish products continues to rise, quality has become a key factor in market competition. Ecological aquaculture research is exploring various farming methods to balance high-quality demand with environmental protection. This study compared three aquaculture models—cage culture (CG), recirculating aquaculture (RAG), and rice–fish co-culture (RG)—by analyzing muscle quality (AOAC, GC-MS), intestinal microbiota (16S rRNA), and liver metabolism (LC-MS) to assess their effects on M. albus. In terms of muscle quality, the RG group showed increased levels of EPA and DHA, reduced muscle moisture and crude lipid content, and enhanced crude protein accumulation. The crude protein content was significantly higher in the RAG group than in the CG group (p < 0.05). The RG group also had the highest levels of total, essential, and umami amino acids, followed by the RAG and CG groups. In terms of intestinal microbiota, the RG group had the highest microbial diversity and stability, with increased abundance of Firmicutes and Bacteroidetes and decreased levels of Proteobacteria. Compared to the CG, the RAG group also showed increased microbial diversity and a reduction in pathogenic genera. Liver metabolomics analysis demonstrated that the RG group had significant advantages over the CG group in amino acid, lipid, and energy metabolism. The RAG group exhibited upregulation of glycerophospholipid metabolism and a decrease in oxidative stress marker levels. Overall, the RG group enhanced muscle quality and optimized intestinal and liver metabolism in M. albus.

Medium-chain fatty acid triglycerides (MCTs) possess antibacterial, antiviral, nutritional, and other biological activities and have demonstrated significant application potential in humans and terrestrial animals. In recent years, with the development of the green aquaculture industry, MCTs have been gradually applied to aquaculture animals, which can enhance growth performance, improve flesh quality, regulate lipid metabolism, boost immune activity, and modulate the intestinal flora, thereby improving the production efficiency of aquaculture. This paper elaborates in detail on the biological activities of MCTs and their applications in aquatic animals, providing a theoretical and practical basis for the application of MCTs in aquaculture.