There is considerable interest in improving hatchery production of the mud crab, Scylla serrata. Although some progress has been made toward identifying appropriate feeding protocols for live-foods, the density at which food is first provided to larvae varies greatly in practice. This study examined relationships between rotifer density and activity patterns of enzymes critical to digestion in S. serrata to evaluate feeding protocols from a nutrient utilization perspective. Activities of trypsin-like proteases, nonspecific esterases, and α-amylase were quantified to determine the response of newly hatched (Zoea I) larvae of S. serrata to rotifers provided at four different densities (i.e., 10, 20, 40, and 80 mL^–1) from first-feeding. Results showed that rotifer density significantly (P < 0.01) influenced total activity (mU larva^–1) patterns within 24 h of first-feeding for all the enzymes assayed. Based on these patterns, utilization of the associated macronutrients (i.e., protein, lipid, and carbohydrate) was presumably similar when larvae were provided with rotifers at densities of 10, 20, or 40 mL^–1 and increased when larvae were provided with rotifers at a density of 80 mL^–1. An optimal density at which to provide rotifers to S. serrata for first-feeding is likely to be >40 mL^–1. The comparative analyses of enzyme activities presented in this study represent an innovative approach to quickly (within 24 h) identify optimal food densities for larval crustaceans at first-feeding.