Ghrelin is implicated in growth and feeding regulation in fish. The influence of ghrelin on behavior has not been well studied and the physiological role of des-fatty acid modification of this peptide is unclear. Therefore, the effects of intracerebroventricular (ICV) and intraperitoneal (IP) administration of synthetic n-octanoylated (acyl) goldfish ghrelin and des-n-octanoylated (des-acyl) ghrelin on locomotor and orexigenic activity in the goldfish were examined. ICV administration of acyl ghrelin at doses of 1 and 2 pmol/g body weight (BW) and IP administration at 16 pmol/g BW both induced significant increases in locomotor activity during for 45-60 min after treatment. Cumulative food intake was significantly increased by ICV injection of acyl ghrelin at doses of 1 and 2 pmol/g BW and IP injection at 8 and 16 pmol/g BW during the 60-min post-treatment observation period. In contrast, ICV and IP administration of des-acyl ghrelin produced no changes in locomotor and orexigenic activity. We also analyzed fasting-induced changes in the expression of ghrelin mRNA in the brain and intestine using a real-time PCR method. The level of ghrelin mRNA in the intestine, but not in the brain, obtained from fish fasted for 7 days was significantly higher than that in fish that had been fed normally. These results suggest that, in the goldfish, acyl ghrelin, but not des-acyl ghrelin, stimulates locomotor activity and enhances food intake via central and peripheral pathways.