The impact of various periods of mercury exposure on the osmoregulatory and blood gas parameters of tilapia (Oreochromis niloticus)

Mercury (Hg) poses a significant risk to aquatic ecosystems and living organisms as a result of human activities. Hg found in fish can be detrimental to human health when consumed, causing harmful effects. The potential impact of Hg on fish physiology is a significant concern, given its presence in fish. The rapid accumulation of Hg in fish tissues has the potential to impact their blood gas and electrolyte compositions. The objective of this investigation was to analyze the effects of sublethal concentrations of Hg on the blood gas and electrolyte levels of tilapia (Oreochromis niloticus) over different periods of exposure. This research was conducted through laboratory experiments. The study involved subjecting fish to sublethal concentrations of Hg at levels of 0.06 and 0.6 mg/L for a duration of 4 and 15 days. Upon completion of the toxicity test, fish specimens were taken from each testing group for the purpose of analyzing the Hg and carbonic anhydrase (CA) concentrations present in the gills, as well as osmoregulatory, acid-base, and hematological parameters. The results indicate that solely the fish that were subjected to a concentration of 0.6 mg/L Hg for a duration of 15 days exhibited a higher concentration of Hg in their gills compared to the control group. The inhibition of respiration by Hg was observed to be a result of the generation of metabolic acidosis, reduction in gill CA, decrease in pO₂, as well as a decrease in plasma osmolality, Cl⁻, Na⁺, and K⁺. The levels of red blood cells, hemoglobin, and hematocrit exhibited a decrease solely at the concentration of 0.6 mg/L over a period of 15 days. The previously mentioned impairments have the potential to restrict the capacity of fish to adequately supply oxygen to their cells, thereby reducing overall performance.