Supplementation of potassium, magnesium and sodium chloride in practical diets for the Pacific white shrimp, Litopenaeus vannamei, reared in low salinity waters

The culture of Litopenaeus vannamei in inland low salinity waters is currently being practiced in various countries around the world. These environments are often deficient in key ions essential for normal physiological function, including potassium (K+) and magnesium (Mg2+). Farmers have sometimes been able to counteract ionic deficiencies in the water profile by adding mineral salts containing sources of K+ and Mg2+. The purpose of this study was to explore the possibility of correcting deficiencies of K+ and Mg2+ in the water profile with dietary supplementation of these minerals. Two separate 7-week experiments were conducted in 4.0 g(-1) artificial low salinity water to evaluate the effects of mineral supplements (K+, Mg2+ and NaCl) to diets of L. vannamei reared in low salinity waters. In trial I seven diets were formulated (10 g NaCl kg(-1), 20 g NaCl kg(-1), 150 mg kg(-1) Mg2+, 300 mg kg(-1) Mg2+, 5 g K+ kg(-1), 10 g K+ kg(-1), and a basal diet to serve as a control). Minerals were added in the form of purified potassium chloride (KCl), magnesium chloride (MgCl2 center dot 6H(2)O) and NaCl. Trial 2 evaluated the use of a coating agent for the Mg2+ and NaCl treatments, while a K+ amino acid complex was utilized in the K+ treatments to reduce mineral leaching. Trial 2 was performed using similar treatment levels as trial 1. Shrimp survival and growth were assessed in both experiments. Results from trial I indicated no significant differences in survival, growth or percent weight gain. Results from trial 2 revealed no significant differences in Survival and growth in the NaCl and Mg2+ treatments. However, significant differences in growth (P < 0.05) were observed when using the 10 g K+ kg(-1) treatment, suggesting that dietary supplementation of a K+ amino acid complex may help improve growth of the species in low salinity waters.