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Background. Cadmium (Cd) can contaminate aquatic environments as a result of anthropogenic activity. Cd accumulates quickly in the tissues of fish and has the potential to affect their physiology, including osmoregulation and acid-base balance. Therefore, the purpose of this study was to examine the sublethal effects of Cd on the osmoregulation and acid-base balance of tilapia Oreochromis niloticus at different times. Methods. Fish were exposed to sublethal concentrations of Cd (1 and 2 mg/L) for 4 and 15 days. At the end of the experiment, fish were collected from each treatment to examine the levels of Cd and carbonic anhydrase (CA) in the gills, plasma osmolality, ions, blood pH, pCO2, pO2, and hematological parameters. Results. Cd concentrations in gills rose with increasing Cd concentrations in the medium and exposure time. Cd inhibited respiration by generating metabolic acidosis, decreasing gill CA, reducing pO2, plasma osmolality, Cl−, and K+, particularly at 2 mg/L for 4 days and 1 and 2 mg/L for 15 days. Red blood cell (RBC), hemoglobin (Hb), and hematocrit (Ht) levels decreased as Cd levels in water and exposure duration increased. Conclusion. Cd inhibits respiration, lowers RCB, Hb, and Ht levels and decreases ionic and osmotic regulation. All of these impairments can limit a fish’s ability to provide appropriate oxygen to its cells, hence diminishing its physical activity and productivity.

Background. Cadmium (Cd) can contaminate aquatic environments as a result of anthropogenic activity. Cd accumulates quickly in the tissues of fish and has the potential to affect their physiology, including osmoregulation and acid-base balance. Therefore, the purpose of this study was to examine the sublethal effects of Cd on the osmoregulation and acid-base balance of tilapia Oreochromis niloticus at different times. Methods. Fish were exposed to sublethal concentrations of Cd (1 and 2 mg/L) for 4 and 15 days. At the end of the experiment, fish were collected from each treatment to examine the levels of Cd and carbonic anhydrase (CA) in the gills, plasma osmolality, ions, blood pH, pCO2, pO2, and hematological parameters. Results. Cd concentrations in gills rose with increasing Cd concentrations in the medium and exposure time. Cd inhibited respiration by generating metabolic acidosis, decreasing gill CA, reducing pO2, plasma osmolality, Cl-, and K+, particularly at 2 mg/L for 4 days and 1 and 2 mg/L for 15 days. Red blood cell (RBC), hemoglobin (Hb), and hematocrit (Ht) levels decreased as Cd levels in water and exposure duration increased. Conclusion. Cd inhibits respiration, lowers RCB, Hb, and Ht levels, and decreases ionic and osmotic regulation. All of these impairments can limit a fish's ability to provide appropriate oxygen to its cells, hence diminishing its physical activity and productivity.

Tilapia exposed to two different Cd concentrations in freshwater had varying levels of Cd in their gills, with fish exposed to 2 mg/L of Cd having a higher Cd level than fish exposed to 1 mg/L of Cd. The higher Cd level exposure caused considerable metabolic acidosis (lower pH and higher pCO2) and inhibited gill carbonic anhydrase. Fish exposed to higher Cd levels had lower osmolality, levels of plasma Cl− and K+ but constant levels of Na+. All hematological parameters tested in this study, including red blood cells, hemoglobin, hematocrit, and mean cellular hemoglobin concentration hematocrit, decreased as a result of increased Cd exposure. This is consistent with the pO2 measurement, which indicates that fish exposed to greater levels of Cd had a considerable reduction in pO2.

Tilapia exposed to two different Cd concentrations in freshwater had varying levels of Cd in their gills, with fish exposed to 2 mg/L of Cd having a higher Cd level than fish exposed to 1 mg/L of Cd. The higher Cd level exposure caused considerable metabolic acidosis (lower pH and higher pCO2) and inhibited gill carbonic anhydrase. Fish exposed to higher Cd levels had lower osmolality, levels of plasma Cl− and K+ but constant levels of Na+. All hematological parameters tested in this study, including red blood cells, hemoglobin, hematocrit, and mean cellular hemoglobin concentration hematocrit, decreased as a result of increased Cd exposure. This is consistent with the pO2 measurement, which indicates that fish exposed to greater levels of Cd had a considerable reduction in pO2.