C. sapidus is of considerable culinary and economic importance in the United States, particularly in Louisiana, the Carolinas, the Chesapeake Bay, Delaware, and New Jersey. It is the Maryland state crustacean and the state's largest commercial fishery. Due to overfishing and environmental pressures some of the fisheries have seen declining yields, especially in the Chesapeake Bay fishery.
A blue crab grows by shedding its exoskeleton, or molting, to expose a new, larger exoskeleton. After it hardens, the new shell fills with body tissue. Shell hardening occurs most quickly in low-salinity water where high osmotic pressure allows the shell to become rigid soon after molting. Molting reflects only incremental growth, making age estimation difficult. For blue crabs, the number of molts in a lifetime is fixed at about 25. Females typically exhibit 18 molts after the larval stages, while postlarval males molt about 20 times. Male blue crabs tend to grow broader and have more accentuated lateral spines than females. Growth and molting are profoundly influenced by temperature and food availability. Higher temperatures and greater food resources decrease the period of time between molts, as well as the change in size during molts (molt increment). Salinity and disease also have subtle impacts on molting and growth rate. Molting occurs more rapidly in low-salinity environments. The high osmotic pressure gradient causes water to quickly diffuse into a soft, recently molted blue crab's shell, allowing it to harden more quickly. The effects of diseases and parasites on growth and molting are less well understood, but in many cases have been observed to reduce growth between molts. For example, mature female blue crabs infected with the parasitic rhizocephalan barnacle Loxothylacus texanus appear extremely stunted in growth when compared to uninfected mature females. Blue crabs may reach maturity within one year of hatching in the Gulf of Mexico, while Chesapeake Bay crabs may take up to 18 months to mature. As a result of different growth rates, commercial and recreational crabbing occur year-round in the Gulf of Mexico, while crabbing seasons are closed for colder parts of the year in northern states.