Novel Aspects of Phosphate Endocrine Control: A Key Element for the Long-Term Sustainability of Finfish Aquaculture

Phosphorus, in the form of inorganic phosphate (Pi), is one of the most important macronutrients for all organisms, including fish. Among other functions, it is indispensable for the formation and development of hard tissues such as bones and scales. However, its deficiency has implications not only for those hard tissues, where it is responsible for defective mineralization, leading to skeletal malformation, but also for disturbances of intermediary metabolism, especially energy metabolism, leading to impairment of growth. Nevertheless, the endocrine mechanisms for regulation of Pi balance in fish have largely been overlooked. Currently, in commercial fish culture systems Pi enriched diets are generally used to avoid skeletal malformations ensure health and increase growth but, however, excess levels can have harmful effects on fish. Additionally, the excess of unused/excreted Pi in the effluents from these culture systems turns intensive fish farming in a major source of eutrophication in the aquatic systems. Therefore, the improvement of foods used and the reduction of the outputs of these dissolved wastes it will be a key element for the long-term sustainability of aquaculture. One of the fundamental points to achieve this goal is to understand the mechanisms that regulate Pi homeostasis in fish, which ultimately will contribute to the equilibrium between the requirements for optimal physiology, fast growth and reduced environmental impact. Therefore, in this chapter, we attempt to describe the current state of knowledge regarding the recently characterized endocrine and non-endocrine factors involved in the regulation of phosphate homeostasis in fish.