Background adaptation is used by teleosts as one of a variety of camouflage mechanisms for avoidance of predation. Background adaptation is known to involve light sensing by the retina and subsequent regulation of melanophore dispersion or contraction in melanocytes, mediated by α-melanocyte-stimulating hormone and melanin-concentrating hormone, respectively. Here, we demonstrate that an agouti gene unique to teleosts, agrp2, is specifically expressed in the pineal and is required for up-regulation of hypothalamic pmch and pmchl mRNA and melanosome contraction in dermal melanocytes in response to a white background. floating head, a mutant with defective pineal development, exhibits defective up-regulation of mch mRNAs by white background, whereas nrc, a blind mutant, exhibits a normal response. These studies identify a role for the pineal in background adaptation in teleosts, a unique physiological function for the agouti family of proteins, and define a neuroendocrine axis by which environmental background regulates pigmentation.