Alterations in the immunological parameters of Tench (Tinca tinca L. 1758) after acute and chronic exposure to lethal and sublethal treatments with mercury, cadmium and lead

Tinca tinca were exposed to lethal and sublethal treatments with mercury, cadmium and lead for acute and chronic periods to study alterations in immunological parameters. Acute lethal exposure (Lc(50)/48 h; 96-h Lc(50) of Hg 1.0, Cd 6.5, Pb 300 ppm) caused a significant increase in Lct in the Hg treatment and a significant decrease in the Pb treatment, and a significant decrease in total WBC count in the Hg and Cd treatments. Lower acute sublethal exposures (10% Lc(50)/24 h), caused a significant increase in Lct in the Hg and Pb, treatments and a significant increase in total WBC count in the Hg treatment. The same concentration after 96-h exposure resulted in a significant increase in Lct in all 3 treatments and a significant decrease in total WBC count in the Cd treatment, and after chronic exposure caused a significant increase in Lct in the Hg treatment and a significant increase in total WBC count in the Hg and Cd treatments. Higher acute sublethal exposures (25% LC50/24 h) caused a significant increase in Lct in the Hg and Cd treatments and a significant increase in total WBC count in all 3 treatments. The same concentration after 96-h exposure caused a significant increase in both Lct and total WBC count in all 3 treatments, and after 3 weeks exposure resulted in a significant increase in Lct in the Hg treatment and a significant increase in total WBC count in the Hg and Pb treatments and a significant decrease in the Cd treatment. The hypothesized greater resistance of tench to mercury, cadmium and lead toxicity compared to other fish species did not prove true: however, it was evident from the data that both acute and chronic metal exposure caused immunological impairment in tench, which suggests that the metals may weaken the immune system, resulting in increased susceptibility to infections. Further, the toxicity order of metals for the hernatological parameters of tench was Hg > Cd > Pb.