Cittarium pica is an endangered Caribbean gastropod of ecological and economic importance. In order to provide the basis for the aquaculture development and/or population management of this species, the relationships among its body size and physiological variables associated with the energetic balance were assessed. Individual measurements of rates of egestion (ER), ingestion (IR), absorption (AR), oxygen consumption (OCR), ammonia excretion (UR), mucus production (MR), absorption efficiency (AE) and scope for growth (SFG), were carried out on specimens between 0.01 and 12.07 g of dry weight of the soft parts (DW) under controlled laboratory conditions. Most of the variables showed positive potential relationships with the DW of the animals (ER mg h-1 = 1.51 DW0.37, IR mg h-1 = 4.13 DW0.32, AR = 2.56 DW0.30, OCR mL O2 h-1 = 0.38 DW0.74, UR μg NH4 -N h-1 = 19.17 DW0.78, MR mg h-1 = 1.28 DW0.14 and SFG = 36.92 DW0.22). AE did not show any relationship with this variable. The large snails had faster input and output of energy compared to the small specimens, also having proportionally greater energetic expenditures, mucus production, and energetic balance.