Leptin is a hormone secreted from white adipocytes and plays important role in the regulation of food intake and energy balance. Leptin functions via signaling pathways involving OB-R in hypothalamus. In mammals, leptin is mainly produced by the adipose tissue and encodes body fat reserves, acting as a short-term satiety signal. In fish, the presence of a leptin-like peptide was first evidenced by immuno-cross-reactivity, and its existence was certainly demonstrated after the finding by synteny of a leptin sequence in the pufferfish.