Metabolomic and transcriptomic profiling reveals the effect of dietary protein and lipid levels on growth performance in loach ().

The subject of this study was to explore the optimum requirements of loach () regarding dietary proteins and lipids and discuss the underlying mechanism. We designed nine diets to determine the effects of different levels of dietary crude protein (CP: 30%, 35%, and 40%) and ether extract (EE: 6%, 10%, and 14%) on the growth performance and metabolism of . In total, 2160 healthy (5.19 ± 0.01 g) were divided into nine groups with four replications at 60 fish per barrel stocking density. The trial lasted for eight weeks. Serum and liver samples were gathered for metabolomic and transcriptomic analyses. The results showed that the specific growth rate of in the CP40EE10 group was the fastest and notably higher than that in other groups ( 0.05). Analysis of the metabolome results found that the mTOR signaling pathway, glycerophospholipid metabolism, D-arginine and D-ornithine metabolism were significantly enriched pathways in the CP40EE10 group compared with the other groups ( 0.05). Moreover, the transcriptomic analysis of differentially expressed genes (DEGs) showed that the expression of (arginase) involved in protein synthesis was significantly upregulated in the CP40EE10 group compared to the slowest growing group (< 0.05). Additionally, the expression of (secretory phospholipase A2) involved in lipid metabolism and (fructose-1,6-bisphosphatase) involved in glucose metabolism were all significantly downregulated in the CP30EE6 group compared with the CP40EE10 group (< 0.05). Furthermore, the analysis of differentially expressed metabolites (DEMs) and DEGs co-enriched in the KEGG pathway revealed that the significantly enriched pathways were arginine and proline metabolism, glycerophospholipid metabolism, and glycolysis/gluconeogenesis in CP40EE10 compared with other groups (< 0.05). We conclude that including 40% CP and 10% EE in the diet could result in a better growth rate. We hypothesized from metabolomic and transcriptomic analyses that the CP40EE10 diet might promote the growth of by promoting protein synthesis, lipid metabolism, and energy production.