The endocrine regulation of growth and appetite in fish has been partially characterized in a handful of species, most notably, goldfish, salmonids and catfish. Endocrine modulators, such as growth hormone (GH) and insulin-like growth factor-I (IGF-I) have been best characterized and often correlated to changes in feeding or nutrient intake. The regulatory functions of neuropeptide modulators of growth and appetite, with special emphasis on hypothalamic and gastrointestinal peptides, have also been well published for these species. Perhaps not surprisingly, salmonids and catfishes are among the most studied nutritionally as well, with most of their nutrient requirements being defined. More recently, nutrient sensing studies have shed light on chemosensory detection by fish of water born nutrients and the effect on feeding and metabolism. Even more recently, a focus gut microbiota has led to an explosion of publications on the impacts of genetics, diet and other environmental factors on gut function. Over the past two decades, my lab, like many others, has chipped away at the surface of the interactions between the endocrine system, the gut and even the microbiome. Yet, there is so much left unknown. The very complexity of the gut-brain axis suggests that we have only begun to identify the mechanisms involved in humans and terrestrial lab and farm animals, let alone in fish. While we can learn much from this literature, species-specific research must be a focus for aquaculture species. Only then can we truly develop targeted feeds and feeding protocols to maximize fish performance.