Dietary 5-hydroxytryptophan supplementation improves growth and metabolism of large yellow croaker (Larimichthys crocea) in association with microbiota-gut-brain axis-related changes

The microbiota–gut–brain (MGB) axis and it’s the role in physiology and behaviors of the host with serotonin as a key signaling molecule have received much attention in recent years. 5-Hydroxytryptophan (5-HTP), an effective serotonin precursor, has regulatory effects on the MGB axis, but little is known about these effects in fish. In this study, we assessed the effects of dietary 5-HTP supplementation (0, 50, 100, and 200 mg/kg) on the growth and feed utilization, morphological indices and body composition, antioxidant and digestive enzyme activity, intestinal morphology, the gut microbiota and its metabolites (short-chain fatty acids), and the transcriptomic profiles of the gut and hypothalamus of large yellow croaker ( Larimichthys crocea ). 5-HTP supplementation had an impact on weight gain, the feed conversion ratio, and the body contents of crude lipid and ash. 5-HTP supplementation increased total antioxidant capacity and glutathione peroxidase activity in plasma and superoxide dismutase activity in the liver; lipase and amylase activity was greatest in fish supplemented with 100 mg/kg 5-HTP. These results showed that 100 mg/kg 5-HTP could improve growth performance, and enhance antioxidant capacity and digestive ability. In addition, 100 mg/kg 5-HTP affected the gut microbiota, increased the propionic acid and butyric acid contents, and caused transcriptome alterations associated with gut–brain communication. The enriched Kyoto Encyclopedia of Genes and Genomes pathways of the differentially expressed genes in the gut were associated with the digestive system, endocrine system, lipid metabolism, and immunity system, while those in the hypothalamus were associated with the nervous system, immunity and inflammation, endocrine system, and development and regeneration. These findings suggest that 5-HTP can serve as a potential aquatic feed additive for improving the growth and metabolism of L. crocea , and the effects may involve metabolic, endocrine, neural, and immune pathways associated with the MGB axis.