Ligand for growth hormone secretagogue receptor type 1 (GHSR). Induces the release of growth hormone from the pituitary. Has an appetite-stimulating effect, induces adiposity and stimulates gastric acid secretion. Involved in growth regulation. Highest levels in stomach and anterior intestine. Lower levels in posterior intestine, kidney and brain. Low levels in heart, head kidney and middle intestine. O-octanoylated by GOAT/MBOAT4 (By similarity). O-octanoylation or O-decanoylation is essential for activity. The O-decanoylated form ghrelin-21-C10 differs in the length of the carbon backbone of the carboxylic acid forming an ester bond with Ser-29. 44% of eel ghrelin is O-decanoylated (PubMed:12630926). Ghrelin-21-C10, O-decanoylated form. Ghrelin-21-C8, O-octanoylated form. Belongs to the motilin family.