The importance of understanding energy allocation to developing gonads in cultured sea urchins can be summarized in a simple question: 'what is the greatest yield of gonad tissue mass one can obtain with the lowest ration of food?' In considering the growth and development of gonadal tissue as a harvestable resource, the balance between yield and ration can best be described in terms of the chemical constituents that limit gonad growth, i.e., the biochemical components in the shortest supply (. ration) restrict development of the gonad tissues (. yield). In this chapter we consider the metabolic activities in the sea urchin gonad in relation to an individual's diet to identify the tissue constituents that have the highest anabolic costs and are thus the most likely to restrict or limit tissue production. Although whole-animal, energy metabolism (respiration and biochemical pathways) has been well studied in adult urchins, we focus specifically on what little is known about the metabolic activities in sea urchin gonads. © 2013 Elsevier B.V.