Enables melanocortin receptor activity. Involved in energy homeostasis and energy reserve metabolic process. Acts upstream of or within adenylate cyclase-activating G protein-coupled receptor signaling pathway; negative regulation of feeding behavior; and regulation of growth. Predicted to be located in membrane. Predicted to be active in cytoplasm and plasma membrane. Is expressed in brain; female organism; gonad; myotome; and primary motor neurons. Human ortholog(s) of this gene implicated in morbid obesity and obesity. Orthologous to human MC4R (melanocortin 4 receptor).