L. vannamei is a highly adaptable euryhaline species. It has been produced in different production systems over a wide range of environmental salinities. Compared to seawater, the ionic profile of inland low salinity sources can be dramatically different, varying markedly among sites and having low and variable concentrations of Mg2+ and K+. Several approaches have been investigated to improve shrimp production in low salinity waters (LSW) in Alabama including modification of the waters ionic composition and dietary modifications. While Mg2+ is supplemented at the beginning of each production season by commercial shrimp producers, the target concentration used by Alabama farmers (>20 mg/L) may not be high enough, particularly for larger shrimp in the later phase of the production cycle as shrimp farmers have reported increased mortality during this specific stage in ontogeny. In order to investigate this issue, two studies were conducted on a commercial shrimp farm in west Alabama. In the first study, additional Mg2+supplemented to production ponds was evaluated to determine if increases in survival, growth, and production of L. vannamei reared in LSW could be achieved. In this study, a total of 10 commercial production ponds (ranging in size from 0.4 to 3.2 hectares) were used. Shrimp were stocked into each pond at a density of 271,800 sperm/ha and offered a commercial feed twice a day. An initial amount of Mg2+present in a fertilizer, so that sulfate of potash magnesia (K2SO4MgSO4), was used as a source of both K+ and Mg2+ by the farm for each pond to attempt to raise Mg2+ levels in ponds to 20 mg/L. After stocking, an agricultural grade magnesium chloride (MgCl2) was used to quadruple (~80 mg/L) the amount of Mg2+ in four commercial shrimp ponds while another six commercial ponds served as the experimental control. Pond water was sampled at the beginning of the trial, each month, and before harvest to determine pond ionic profiles (Na+, K+, Mg2+, Ca2+). Shrimp were sampled monthly for hemolymph osmolality, hemolymph ions, and whole-body ion composition. The second study evaluated survival and growth performance of larger shrimp (>15 g) reared in two on-levee flow through-tank systems. One tank system received water from a production pond containing the standard amount of Mg2+ (20 g/L) compared to a similar tank system with water sourced from a production pond with four times the amount of magnesium. Twelve tanks (800-L) were stocked with shrimp at three different densities (20, 25, 30 shrimp/tank). Following 8 weeks, tanks were harvested to determine production performance of shrimp and preliminary analysis indicated there were no differences in survival, growth, weight gain (%), or food conversion ratio (all p < 0.05) in shrimp reared at different densities in waters of varying Mg2+ composition. Analysis of hemolymph osmolality, hemolymph ions, and whole-body ion composition are ongoing. Data from these trials will help determine whether additional Mg2+ can increase survival, growth, and production of larger L. vannamei reared in LSW.