Change of osmoregulatory and hematological parameters in tilapia (Oreochromis niloticus) after exposure to sublethal mercury concentrations

Abstract

The effects of Hg exposure on blood parameters and gill physiology of tilapia (Oreochromis niloticus) were analyzed. Fish maintained in freshwater were exposed for 7 days (d) to sublethal mercury concentrations (0.1 and 1 mg/L). Blood serum osmolality (SO), sodium (Na+), potassium (K+) and chloride (Cl−) ionic concentrations, and hematological parameters were assessed after 1 up to 7 d of exposure. Serum osmolality and ionic concentrations of exposed fish appeared differently affected throughout the experimental period compared to the controls. Osmolality was reduced at the 2 tested concentrations but Na+ and Cl− contents were only altered at 1 mg/L of Hg after 1 d of exposure and values rapidly returned to the control values thereafter. K+ content was also modified and significantly increased at both concentrations after 1 d of exposure but returned to the control values after 3 d of exposure. Red blood cell (RBC), white blood cell (WBC) and hemoglobin (Hb) levels were significantly increased throughout the experiment but returned to control values after 7 d of exposure only for the 0.1 mg/L concentration. The hematocrit (Ht) levels remained unaffected due to Hg exposure. Therefore, tilapias exposed to sublethal concentrations of Hg present a marked osmotic imbalance with ionic and hematological disorders that are rapidly compensated.

Keywords

• Mercury
• Tilapia
• Osmoregulation
• Serum ions
• Blood
• Aquatic toxicology