Effects of salinity and Na⁺/K⁺ ratio on survival and histological structure of Litopenaeus vannamei

By using method of experimental ecology, we studied the effects of salinity (2, 4, 8, 12, 16) and Na⁺/K⁺ (27, 50, 75, 100, 125 and 150) ratio on 72 h survival rate, hepatopancreas and muscle structure of Litopenaeus vannamei juveniles with body mass of (1.35 ± 0.37) g under experimental condition. The results show that survival rate of L. vannamei decreased with increasing salinity when the Na⁺/K⁺ ratio was above 75. In addition, when the water salinity was over 8, the survival rate increased with decreasing Na⁺/K⁺ ratio. The survival rate of L. vannamei was above 66.67% when the Na⁺/K⁺ ratio was 27−75. When the Na⁺/K⁺ ratio was 100, the half lethal time (LT₅₀) of L. vannamei was 69.78 and 60.15 h at salinity of 12 and 16, respectively. When the Na⁺/K⁺ ratio was 125, the LT₅₀ at salinity of 8, 12 and 16 was 76.23, 62.61 and 49.10 h, respectively. When the Na⁺/K⁺ ratio was 150, the LT₅₀ at salinity of 4, 8, 12 and 16 was 87.24, 68.65, 59.4 and 39.95 h, respectively. Based on the two-factor variance analysis, the 72 h survival rate of L. vannamei was significantly influenced by salinity, Na⁺/K⁺ ratio and their interactions (P<0.001). Histopathology observation reveals that high Na⁺/K⁺ ratio can cause abnormal histological change in shrimp muscle and hepatopancreas, such as cell vacuolation or autolysis, larger intercellular space, fuzzy and disordered boundary between tissues. In general, potassium deficiency can aggravate the tissue injury of L. vannamei with higher salinity.