Abstract:Ghrelin, an appetite-promoting gastrointestinal peptide, is involved in the feeding regulation of vertebrates. Mandarin fish (Siniperca chuatsi) is a typical carnivorous fish. It feeds on live bait throughout its life since its birth and is mainly fed with live bait during its production. In recent years, mandarin fish feed domestication research and experiments on compound food have also made rapid progress. However, compared to live bait feeding, the food intake decreased significantly after compound feed domestication. Ghrelin is the only foodpromoting factor in the periphery. Whether the decrease in food intake after compound feed acclimation is related to the regulation effect of ghrelin remains to be studied. We obtained and analyzed the preproghrelin DNA sequence of Siniperca chuatsi for the first time by transcriptome sequencing and genome data matching and located the secretory cells. At the same time, we detected changes in the ghrelin gene and protein expression in the stomach after being induced and fed. The attraction test simulates the sighting of food before feeding but the inability to feed, while the feeding test simulates the normal feeding of mandarin fish. The results showed that the preproghrelin gene contains four exons and three introns and belongs to type II; 107 amino acids are coded, and the mature peptide ghrelin consists of 20 amino acids with GSSF as the active center. Immunohistochemistry revealed ghrelin-production cells located in the gastric glands. In the attraction test, ghrelin mRNA and protein expression levels were significantly higher in the live-bait group (P<0.05). In contrast, ghrelin expression levels did not change significantly in the compound food group and were significantly lower than that in the live bait group. At 0h after feeding, ghrelin mRNA and protein levels in the live bait group increased significantly and decreased to normal levels at 2 h after feeding (P<0.05), with no significant changes in subsequent gastric emptying (P>0.05). Ghrelin mRNA expression levels in the compound food group did not change significantly throughout the feeding trial (P>0.05), but fluctuations in protein levels were detected. In summary, ghrelin, located in the gastric glands, is involved in feeding regulation activities and shows a tendency to increase before and decrease after feeding. Additionally, compound food feeding reduced the effect of ghrelin on food regulation.