The intracerebroventricular (icv) or intraperitoneal (ip) injection of MC4R agonists can decrease food intake in goldfish [19], zebrafish [3], and coho salmon [20], while transgenic zebrafish over-expressing AgRP display obesity, increased linear growth, and adipocyte hypotrophy [17]. Here, MC4R is linked to obesity due to melanocortin 4 receptor deficiency.