Biomass accumulation and changes in body energy and nutrient (carbon, nitrogen, and phosphorus) composition were evaluated relative to the migration pattern of gulf menhaden (Brevoortia patronus) to determine if biotic transport by fish is an important source of energy and nutrients to coastal marine ecosystems. Gulf menhaden transported significant quantities of energy, C, N, and P from a Louisiana estuary to the nearshore Gulf of Mexico. Transport was always out of the estuary to the marine system, although the magnitude depended on the balance between growth and mortality rates and abundance of fish. Average export per year was 38 g biomass, 930kJ, 22.5 g C, 3.1 g N, and 0.9 g P·m-2 out of estuaries. This is roughly 5-10% of the total primary production of these estuarine areas. N and P export by fish is of the same magnitude as passive waterborne export; however, it is higher quality. This indicates that fish migration can play an important role in exporting the productivity of estuaries to coastal marine ecosystems.