Abstract
The study of nutritional physiology involves unmasking the mechanisms by which nutrients are extracted from food and utilized for maintenance, growth, reproduction, and health of the fish. To best understand fish nutrition, a basic understanding of trophic systems, fish biology, and alimentary tract anatomy among the most diverse group of vertebrates, as well as the processes of food acquisition and digestion and nutrient absorption and utilization, is needed. Intertwined with these processes are complex chemical and cellular messenger systems whose primary functions are to regulate gut function and health, the gut microbiome, and the gastroenteropancreatic system. None of these processes work in isolation, and all of them impact fish nutrition. These important aspects of nutritional physiology are discussed and briefly contextualized considering the impacts of plant-based ingredients in aquafeeds.