Demand and effect of potassium, magnesium, and calcium chlorides on hemolymph parameters, immune-related gene expression, and growth of Litopenaeus vannamei, Boone (1931) under biofloc technology

The ionic composition of culture water may be a more important limiting factor than the salinity itself and may lead to osmotic stress which may influence growth and survival of shrimp culture. The uptake rate and the effect of magnesium chloride (MgCl2), calcium chloride (CaCl2), and potassium chloride (KCl) salts in juveniles of whiteleg shrimp (Litopenaeus vannamei) cultured with biofloc technology (BFT) was evaluated for 62 days in seawater (30 practical salinity unity). Five treatments were analyzed in triplicate: T1; control (water exchange rate of 5% daily), T2; adding CaCl2 + MgCl2 + KCl, T3; adding MgCl2 + KCl, T4; adding CaCl2 + KCl, and T5; adding CaCl2 + MgCl2. Mineral salts were added to water and the response of experimental parameters: physicochemical variables of water quality, osmotic pressure, total hemocyte count, glutathione peroxidase gene expression, superoxide dismutase, and zootechnical variables of the shrimp was assessed. The uptake of single chloride salts (CaCl2, MgCl2, and KCl) by shrimp varied as a function of the concentrations and the ratio of these three ions. Magnesium deficiencies in the culture medium increased CaCl2 and KCl uptake without showing gene expression of SOD and GPx. The best survival rate was obtained by adding the three ions (T2) and the control (T1, water exchange of 5%). We concluded that L. vannamei can be maintained by the addition of essential chloride ions in BFT without water replacement.