Oxygen consumption and ammonia excretion rates were investigated in youngOctopus maya(hatching to 139 days old; 0.11–81.23 g wet body weight, BW; 22.5–23.9°C), young squids ofLoligo forbesi(hatching to 45 days old; 9.4–115.3 mg BW; 12.3–13.1°C) and young squids ofLolliguncula brevis(2.00–39.98 g BW; 23.8–24.7°C). Except at hatching, oxygen consumption and ammonia excretion rates on an individual basis(M)of these three cephalopods increased linearly with increasing body weight(BW)expressed asM = aBWb. Values ofbfor oxygen consumption were 0.900, 0.910 and 0.848 and for ammonia excretion were 0.744, 0.809 and 0.751 forO. maya, L. forbesiandL. brevis, respectively. Among the three species the valueavaried widely, whilebwas similar for both oxygen consumption and ammonia excretion rates. Based upon these data, metabolism for hatchlings ofO. mayaandL. forbesiwas estimated to be relatively lower than that of older juveniles. The O/N ratios for hatchlings ofO. mayaandL. forbesiwere relatively high and indicate an apparent dependence upon lipids in the immediate post‐hatching period, followed by standard protein energy utilization thereafter.