Ligand for growth hormone secretagogue receptor type 1 (GHSR). Has an appetite-stimulating effect, induces adiposity and stimulates gastric acid secretion. Involved in growth regulation (By similarity). Induces the release of growth hormone from the pituitary. Highest levels in the stomach. Moderate levels in the brain, hypothalamus and intestinal tracts. O-octanoylated by GOAT/MBOAT4 (By similarity). O-octanoylation or O-decanoylation is essential for activity. The O-decanoylated forms differ in the length of the carbon backbone of the carboxylic acid forming an ester bond with Ser-29 (By similarity). The majority of trout ghrelin is Ghrelin-20 modified with unsaturated decanoic acid (PubMed:12970156). Ghrelin-20 and Ghrelin-23 are amidated. In some cases, Gly-50 is retained after dibasic amino acid cleavage, to produce non-amidated Ghrelin-21 and Ghrelin-24. With amidation and (C8:1) O-octanoylation. The measured range is 27-49. With amidation and (C8:0) O-octanoylation. The measured range is 27-49. With amidation and (C10:2) O-decanoylation. Major form. The measured range is 27-49. With amidation and (C10:1) O-decanoylation. The measured range is 27-49. With amidation and (C10:0) O-decanoylation. The measured range is 27-49. With glycine retention and (C8:0) O-octanoylation. The measured range is 27-50. With glycine retention and (C10:2) O-decanoylation. The measured range is 27-50. With glycine retention and (C10:1) O-decanoylation. The measured range is 27-50. With amidation and (C8:0) O-octanoylation. The measured range is 27-49. With amidation and (C10:1) O-decanoylation. The measured range is 27-49. With glycine retention and (C8:0) O-octanoylation. The measured range is 27-50. With glycine retention and (C10:2) O-decanoylation. The measured range is 27-50. Belongs to the motilin family.