We examined potential fertility, egg volume, and water, lipid, and fatty acid content through embryogenesis in a population of female U. rapax from Sebastian Inlet, Florida. Carapace width (CW) ranged from 10.80 to 20.09 mm (N = 184), and each female carried 5000 to 30,000 eggs in the last stage of development. Female CW was found to be a good predictor of the number of eggs in the later stage of development (potential fertility = 7.908 CW^2.7655, R² = 0.749). Egg volume increases (from 0.0079 to 0.0134 mm³) was mildly correlated (r = 0.79) with an increase in egg water content (from 60 to 69%). Egg lipid and fatty acid content decreased through embryogenesis, due to its importance as energy source. The most consumed fatty acids were the monounsaturated (97.81 μg . mg dw⁻¹) followed by the saturated (64.34 μg · mg dw⁻¹) and polyunsaturated (38.69 μg · mg dw⁻¹). Fatty acids 16:0, 18:2n-6, 16:1n-7, and 18:2n-6 are consumed preferentially (39.91, 38.45, 29.4 and 23.93 μg · mg dw⁻¹, respectively), while essential polyunsaturated fatty acids, particularly docosahexaenoic acid (22:6n-3) and eicosapentaenoic acid (20:5n-3), are conserved. Egg fatty acid profile also reflects diet and habitat of adults. A medium-low EPA/DHA ratio suggests U. rapax occupies a medium trophic level. The low ratio (18:1n-7/18:1n-9) and high percentages of 18:1n-9 fatty acid (18%) and essential C₁₈ and C₂₀ polyunsaturated fatty acids (19-23%) suggests adults are omnivores consuming primary producers (like algae and mangrove leaves) and small invertebrates. The high percentage of odd-numbered fatty acids (above 3-3.5%) also suggests scavenger/detritivore behaviour.