The distribution of magnesium is similar to phosphorous with the majority being found in the exoskeleton. Magnesium is found in many enzymes and is essential for several enzymatic processes including protein, lipid and carbohydrate metabolism, muscle and nerve functions, and osmoregulation. Sources of magnesium include crab meal, cottonseed meal, krill meal, rice bran, shrimp meal and wheat bran. Magnesium may be supplemented as magnesium sulfate. Recommended level of magnesium in commercial feeds is 0.2% (Akiyama et al., 1992).