Effects of Na+/K+ and Mg2+/Ca2+ ratios in saline groundwaters on Na+-K+-ATPase activity, survival and growth of Marsupenaeus japonicus postlarvae

The effects of the Na+/K+ and Mg2(+)/Ca2(+) ratios in saline groundwaters on Na+-K+-ATPase activity, survival and growth of Marsupenaeus japonicus postlarvae were investigated. The results indicate that the Na+-K+-ATPase activity, survival rate and weight gain of postlarvae were significantly affected by the Na+/K+ and Mg2(+)/Ca2(+) ratios (P < 0.05). The Na+-K+-ATPase activity of postlarvae, in every treatment, changed corresponding to Na+/K+ and Mg2(+)/Ca2(+) ratios, and came to a stable level after 24 h. There was a negative relation between Na+-K+-ATPase activity and Na+/K+ ratio, while there was a positive relation between Na+-K+-ATPase activity and Mg2(+)/Ca2(+) ratio. Compared with seawater (the Na+/K+ and Mg2(+)/Ca2(+) ratios are 27.8 and 4.64 respectively), the Na+-K+-ATPase activity of the Na+/K+ ratio 36 treatment showed no significant difference, while the Mg2(+)/Ca2(+) ratio 4.5 treatment showed distinct difference. The survival rates and weight gain of postlarvae increased markedly when the suitable amount of K+ and Ca2(+) was added to test water, and arrived at their maximum in the Na+/K+ ratio 20-30 or Mg2(+)/Ca2(+) ratio 4.5 treatment, having no significant difference compared with normal seawater. Therefore, considering the Na+/K+, Mg2(+)/Ca2(+) ratios and the absolute concentration of Mg2(+), Ca2(+) in the experimental saline groundwaters applied to Marsupenaeus japonicus farming, it should be modulated to around 30, 4.5 and 1312 mg/l, 291 mg/l, respectively. (c) 2006 Elsevier B.V. All rights reserved.