Development of reproductive competence (puberty) in vertebrate animals relies on the integration of a wide variety of internal and external cues. These signals provide critical information on when an animal should reproduce: whether it is of sufficient size or energy status to reproduce (metabolic cues), whether conditions are optimal for reproductive success (environmental cues), and whether an appropriate mate is present (social cues). Although the mechanisms involved in integrating this information are not clear, ultimately the onset and completion of puberty involves increases in gonadotropin-releasing hormone (GnRH) signaling and subsequent effects on pituitary gonadotropins (GTHs) and gonadal physiology. In fish, the age of puberty is a key component of the species-specific life history strategy, which has evolved to achieve maximal reproductive fitness. In some fish species, the age of puberty is highly plastic and strongly influenced by body size/energy stores because of the large commitment of body energy stores to the gonad. Thus, fish make excellent models to study the influence of metabolic cues on puberty onset. In fish with long spawning migrations that only spawn once in a lifetime, such as Pacific salmon species, the physiological commitment to mature in a given year is a critical life history event and must be made well in advance of spawning. In this talk, the status of our knowledge of changes in the GnRH-GTH-gonad axis during puberty onset in fish (with emphasis on salmon) and how metabolic cues influence this process will be compared to what is known in mammalian models.