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Abstract
The melanocortin system regulates diverse physiological functions in vertebrates, with unique adaptations in teleosts. Using zebrafish, we characterized two agouti proteins, AgRP and AgRP2. AgRP2, expressed in the pineal gland and regulated by light, antagonizes MC1R and mediates background adaptation via pineal-hypothalamic signaling independent of retinal input. AgRP neurons, unlike in mammals, directly project to the pituitary, influencing multiple endocrine axes and somatic growth through MC4R suppression. These findings reveal novel roles for AgRP2 in light-responsive pigmentation and demonstrate hypophysiotropic melanocortin regulation of growth and energy balance in teleosts, highlighting key evolutionary differences from mammals.