A large portion of the total body phosphorous is associated with calcium and is required for exoskeleton formation. Phosphorous serves in many metabolic processes. Phosphorous is an essential component of phospholipids, nucleic acids, phosphoproteins, high energy compounds (ATP), many metabolic intermediates, and coenzymes. Inorganic phosphates also serve as important buffers to maintain normal pH of intra- and extra-cellular fluids (Akiyama et al., 1992).

Phosphorous salts may be absorbed directly from the aquatic environment, however, these concentrations are usually limited. Phosphorous is considered the most limiting mineral in feeds. Sources of phosphorous include dried distillers solubles, cottonseed meal, crab meal, fish solubles, fish meal, krill meal, rice bran and by-products, shrimp meal, squid meal, wheat bran and by-products, and yeast. Sodium phosphate (NaH₂PO₄H₂O) or non-calcium phosphate supplements are recommended as phosphorous supplements. Total phosphorous (approximately 1.5% in feed) needs to be monitored to maintain acceptable calcium:phosphorous ratios (Akiyama et al., 1992).