Effect of exposure to low salinity water on plasma ion regulation and survival rates in artificially wounded devil stinger Inimicus japonicus

We investigated the effect of exposure to low salinity water on plasma ion regulation and survival rates in artificially wounded devil stinger Inimicus japonicus. All fishes survived in 33% seawater (SW), while survival rate in 100% SW was 5.1% at 24 h. In 100% SW, plasma Na+, K+, Mg2+, and Ca2+ concentrations significantly increased to 238 ± 49.9, 9.6 ± 2.4, 15.1 ± 3.5 and 5.0 ± 0.7 mmol/l at 6 h, respectively; the gill Na+/K+–ATPase (NKA) activity was almost stable, although only one fish survived to 24 h. In 33% SW, plasma Na+ and K+ concentrations remained at the same level, and plasma Mg2+ and Ca2+ concentrations gradually increased to 16.2 ± 0.7 and 4.5 ± 0.2 mmol/l until 24 h, respectively. The NKA activity significantly increased to 5.1 ± 1.1 µmol ADP/mg protein per h at 6 h. A positive correlation was observed between the wound surface area against body weight and the plasma ion concentrations, although no difference was observed in the restoration rate of the wounded area between 100 and 33% SW. These results indicate that exposure of wounded fish to low salinity water improves survivability by favoring plasma ion regulation without influencing the restoration rate.