Short-term mercury exposure in tilapia (Oreochromis niloticus) at different salinities: impact on serum osmoregulation, hematological parameters, and Na+/K+-ATPase level

The objectives of this study were to analyze and compare the effects of mercury (Hg) exposure on osmoregulation and hematological responses in East Java strain tilapia (Oreochromis niloticus). Fish were exposed to 0, 0.1, and 1 mg L-1 Hg at 0, 5, 10, and 15 g L-1 salinities, and serum osmolality (SO), ion level, hematological parameters, and sodium (Na+)/potassium (K+)-ATPase (NKA) levels in the gills and kidney were assessed after 96 h of exposure. SO significantly increased in fish exposed to Hg at 15 g L-1 salinity compared with those exposed at 0, 5, 10, and 15 g L-1 salinities, but SO did not significantly increase in fish exposed to Hg at 5 and 10 g L-1 salinities compared with those exposed at 0 g L-1 salinity. At 15 g L-1 salinity, the Na+ level was significantly different from that at 0, 5, and 10 g L-1 salinities. The chloride ion level significantly increased only at 15 g L-1 salinity. Furthermore, the K+ level was significantly different at 10 and 15 g L-1 salinities from that at 0 and 5 g L-1 salinities. Hematocrit and hemoglobin levels and red blood cell and white blood cell (WBC) counts were not significantly different among all salinities. At 15 g L-1 salinity, the NKA level in the gills was significantly different from that at 0 g L-1 salinity, but in the kidney, there was no difference among all salinities. These data provide useful information for future reference and aquaculture practices to reduce Hg effects on tilapia. In conclusion, higher salinity reduced the effect of Hg on the K+ level and WBC count in tilapia.