Short-chain fatty acids affect skeletal muscle composition, fiber recruitment, and metabolism of the small yellow croaker (Larimichthys polyactis)

Recent studies have revealed that intestinal short-chain fatty acids (SCFAs) can affect muscles muscle metabolism in mammals by promoting glycogen metabolism and lipid oxidation. It is still not clear the distinct effect of acetate, propionate, and butyrate on muscle growth and metabolism of animal, especially in fish. This study investigated the differential impacts of acetate, propionate, and butyrate on muscle composition and metabolism in Larimichthys polyactis. A total of 50 adult fish (both farmed and wild) were sampled to analyze intestinal SCFA levels and muscle nutrient composition. Additionally, 945 juvenile fish (average weight: 9.10 ± 0.062 g) were fed diets supplemented with 0.75 and 1.50 g/kg sodium acetate, propionate, or butyrate. Compositional analysis revealed reduced crude protein (CP) and polyunsaturated fatty acid (PUFA) contents in the muscle of farmed L. polyactis compared to wild counterparts. Targeted metabolomics further showed higher SCFA levels in the hindgut of wild fish relative to farmed individuals. Dietary supplementation with SCFAs increased muscle CP and PUFA contents in juvenile fish. Transcriptome analysis indicated that SCFAs upregulated myosin-7 gene expression in muscle and promoted glucose metabolism. Notably, sodium acetate downregulated cysteine sulfinic acid decarboxylase (csad), potentially contributing to reduced muscle fiber diameter. At the 1.50 g/kg supplementation level, sodium propionate and butyrate significantly upregulated very-long-chain enoyl-CoA reductase (tecr) in muscle (P < 0.05). These findings demonstrate that dietary SCFAs improve farmed croaker muscle quality through distinct mechanisms, providing insights for optimizing the muscle quality of farmed fish.