ASSESSMENT OF HEMATOLOGY, SERUM BIOCHEMISTRY AND DNA INTEGRITY IN MAJOR CARPS UNDER THE INFLUENCE OF HEAVY METALS

Abstract

An experiment to assess the changes in hematology, serum biochemistry and DNA integrity in three fish species exposed to metals was conducted under two phases i.e. acute and chronic exposure. During phase I, the experimental fish species i.e. Catla catla, Cirrhinus mrigala and Labeo rohita were exposed to 96-hr LC50 of cadmium (Cd), copper (Cu), nickel (Ni) and zinc (Zn). During phase II, all the fishes were exposed to sub-lethal (1/5th, 1/4th and 1/3rd of LC50) concentrations of the metals for 30-day. During acute exposure, hematological parameters such as red blood cells (RBCs), hemoglobin (Hb), hematocrit (Hct), white blood cells (WBCs), mean cell volume (MCV), mean cell hemoglobin (MCH) and mean cell hemoglobin concentrations (MCHC), and serum biochemical parameters such as sodium (Na), potassium (K), chloride (Cl), albumin (Alb), total protein (TP), urea, glucose, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were examined by collecting the blood samples of control and metals exposed fish after 24-, 48-, 72- and 96-hr. To assess the DNA integrity the liver samples of both control and metals exposed fishes were collected at each of the four sampling hours. RAPD-PCR technique was used to evaluate the effect of metals on DNA integrity of fishes. During chronic exposure, the blood and liver samples were collected after 15- and 30-day of exposure to study all the above mentioned parameters. Metals exposure to the experimental fish species at 96-hr LC50 (acute exposure) and sub-lethal concentrations (chronic exposure) caused significant variability (p<0.01) in hematological parameters as compared to control. Copper exposure to the fish species had more pronounced effects as it resulted in significantly (p<0.01) lower RBCs, Hb, Hct and higher WBCs, MCV, MCH, MCHC while Zn exposure showed least toxic effect towards hematological parameters as compared to other metals. The overall tendencies of the fish species to respond the toxicity of metals by changing their hematological parameters followed the order: C. catla>L. rohita>C. mrigala. Metals-induced changes in hematological parameters of all the fish species became more conspicuous along with the increase in metals concentration i.e. 1/5th<1/4th<1/3rd of LC50. Exposure of metals to the fish for different time durations resulted in significantly variable toxic effects on hematological parameters. Among all the exposure durations of metals, the 96- hr exposure caused maximum negative effects on all the fish species. The 30-day metals exposure caused more toxic effects on all the hematological parameters of fishes as compared to 15-day metals exposure. Fishes also exhibited significant (p<0.01) variability in serum biochemical parameters under the exposure of metals in both acute and chronic phases. Significantly (p<0.01) lower level of serum Na, Cl, Alb and TP were observed in fishes under the exposure of Cu as compared to other metals while K, urea, glucose, AST and ALT levels were higher. However, least toxic effect on all above mentioned biochemical parameters were noticed in Zn exposed fishes. Among fish species, C. catla appeared more sensitive to metals toxicity as compared to L. rohita and C. mrigala. Metals-induced changes in serum biochemical parameters of all the fish species increased concomitantly with the increase in metals concentration i.e. 1/5th<1/4th<1/3rd of LC50. In both acute and chronic phases the toxic effects of metals on the above mentioned serum biochemical parameters became more severe with the increase in exposure duration. During both acute and chronic exposure of metals, the highest DNA damage in terms of percent genomic DNA template stability (% GTS) was observed in Cu exposed fish while the Zn exposure to fish resulted in lowest DNA damage. Regarding the response of fish to the acute toxicity, C. catla appeared more sensitive to toxicity of all the metals followed by L. rohita and C. mrigala. In response to chronic exposure of the metals C. mrigala showed higher DNA damage than L. rohita and C. catla. One third of LC50 of all the metals caused higher DNA damage in terms of GTS (%) while 1/5th of LC50 caused least DNA damage in all the fish species. There were distinct squared Euclidean distances among metals treated and control fishes when the cluster method was applied. The results derived from numerical analysis revealed maximum squared Euclidean distance between Cu treated fishes and the control. In all the fish species, duration based DNA damage was observed during acute exposure of metals while during chronic exposure the DNA damage was both concentration and duration dependent. This study proposed that the occurrence of toxic metals in aquatic environment has strong impact on hematology, serum biochemistry and DNA integrity of the fishes. The observed changes in these parameters may provide valuable information concerning environmental conditions and risk assessment of aquatic organisms.