Effect of various Na/K ratios in low-salinity well water on growth performance and physiological response of Pacific white shrimp Litopenaeus vannamei

To investigate the influence of sodium to potassium (Na/K) ratios on the growth performance and physiological response of the Pacific white shrimp (Litopenaeus vananmei), various concentrations of KCl were added to low-salinity well water (salinity 4) in an 8-week culture trial. Six treatments with Na/K ratios of 60:1, 42:1, 33:1, 23:1, 17:1, and 14:1 were replicated in triplicate. The highest weight-gain rate (3 506 +/- 48)% and survival rate (89.38 +/- 0.88)% was observed in well water with Na/K ratios of 23:1 and 42:1, respectively, while the feed conversion ratio (1.02 +/- 0.01), oxygen consumption, and ammonia-N excretion rate was the lowest in the medium with a Na/K ratio of 23:1. Gill Na+-K+-ATPase activity, as an indicator of osmoregulation, peaked in the treatment where the Na/K ratio was 17:1. The total hemocyte count, respiratory burst, and immune-related enzyme activities (ALP, LSZ, PO, and SOD) of L. vananmei were affected significantly by Na/K ratios (P < 0.05). After challenged with Vibrio harveyi, the cumulative mortality of shrimp reared in a Na/K ratio of 23:1 (30 +/- 14.14)% was significantly lower than the control (75 +/- 7.07)%. In conclusion, the addition of K+ to low-salinity well water in L. vannamei cultures is feasible. Na/K ratios ranging from 23:1 to 33:1 might improve survival and growth. Immunity and disease resistance are also closely related to the Na/K ratio of the low-salinity well water. The findings may contribute to the development of more efficient K + remediation strategies for L. vananmei culture in low-salinity well water.