Minimum environmental potassium for survival of Pacific white shrimp Litopenaeus vannamei (boone) in freshwater

The effect of three essential osmoregulatory ions (Mg2+, K+, and SO42-) on the short-term survival of Pacific white shrimp Litopenacus vannamei in freshwater (<1 ppt total ion concentration) was examined in several experiments. Shrimp postlarvae (PL-18 and -28) were acclimated from seawater (32 ppt) to freshwater (700 ppm TDS: 280 ppm Cl-) over 48 h and held for an additional 24 h before being placed in treatment solutions. Treatments consisted of various Mg2+, K+, and SO42- concentrations in Na+ and Ca2+, solutions that were all derived from chloride or sodium based chemicals added to distilled water. Ten shrimp were placed in triplicate 4-L plastic containers holding 2 L of treatment solutions for 24-48 h. Potassium was found to significantly (P < 0.05) increase shrimp survival, whereas Mg2+ and SO42- had no effect. Solutions with K+ exhibited an average increase in survival of 20% and 42% above solutions without K+ at 24 and 48 h, respectively. This study demonstrates the necessity of K+ in "freshwater" at a minimum concentration of 1 ppm for the survival of this euryhaline marine shrimp. The regulatory aspects involved in maintaining K+ in crustaceans under hypo-osmotic conditions are discussed.