Dietary α-ketoglutarate supplementation enhances growth performance in juvenile red sea bream (Pagrus major) fed low-protein diets by promoting protein synthesis and mitochondrial function

This study evaluated the effects of dietary α-ketoglutarate (α-KG) supplementation at different levels on growth performance, protein synthesis, and mitochondrial function in juvenile red sea bream ( Pagrus major ) fed low-protein (LP) diets. A total of 450 juvenile red sea bream (10.86 ± 0.01 g) were randomly divided into 15 tanks and fed 5 isonitrogenous and isolipidic diets for 9 weeks, including a LP control diet (CON, 42% crude protein) and four α-KG-supplemented diets (0.5%, 1.0%, 1.5%, and 2.0%; designated as A0.5, A1.0, A1.5, A2.0). The results showed that dietary α-KG supplementation improved growth performance and feed utilization ( P < 0.05). At the optimal supplementation level of 1.5%, final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR), feed efficiency ratio (FER), and protein efficiency ratio (PER) increased by 22.65%, 29.19%, 13.73%, 13.27%, and 13.27%, respectively, relative to the CON group, while feed intake (FI) did not differ among treatments. Additionally, α-KG supplementation upregulated activities of hepatic aspartate transaminase (AST) and glutamate dehydrogenase (GDH), increased hepatic glutamate (Glu) content, and promoted protein synthesis via activating the mechanistic target of rapamycin (mTOR) signaling pathway ( P < 0.05). In addition, dietary α-KG upregulated the expression of genes related to mitochondrial biogenesis, fusion, and mitophagy, while downregulating the fission-related gene ( P < 0.05). It also increased the transcription of tricarboxylic acid (TCA) cycle key genes, TCA cycle metabolite contents, and ATP levels ( P < 0.05). In summary, dietary 1.5% α-KG effectively enhances protein synthesis and mitochondrial function in juvenile red sea bream fed LP diets, providing insights into the mechanisms underlying α-KG-mediated growth regulation.