International Journal of Environmental Research University of Tehran ISSN: 1735-6865 EISSN: 2008-2304 Vol. 3, Num. 1, 2009, pp. 95-100

International Journal of Environmental Research, Vol. 3, No. 1, Winter, 2009, pp. 95-100

Heavy Metal Induced Histopathological Alterations in Selected Organs of the Cyprinus carpio L.(Common Carp)

Vinodhini, R.^* and Narayanan, M.

Aquatic Biodiversity Research Centre, Dept. of Advanced Zoology and Biotechnology, St.Xavier’s College (Autonomous), Palayamkottai – 627 002, Tamilnadu, India
*Corresponding author E-mail: swethasivani@yahoo.co.in

Received 10 March 2008; Revised 15 Aug. 2008; Accepted 27 Aug. 2008

Code Number: er09010

ABSTRACT

The hazardous effect of heavy metals on the histopathology of selected organs of the freshwater fish common carp (Cyprinus carpio L.) was investigated. Gill, liver, kidney and flesh samples were collected after 32 days of exposure to a sublethal concentration of 5 mg/L of combined (Cd +Pb+ Cr +Ni) metalsolution containing1.25 mg/Lofeach metal ion (1/10^th ofLC50 / 48h) was analyzed by using light microscopy. The main histopathological changes observed in the gill were edema and lifting of lamellar epithelia. The liver of control fish exhibited a normal structural pattern, while the fish exposed to heavy metals showed vacuolation, presence of hemosiderin and fibrosis. The findings in kidney exhibited the presence of macrophages with lipofuscin granules accumulated in the affected cells. In flesh samples lesions and granulomas were observed. The investigation of histological changes in organs of fish is an accurate way to assess the effects of xenobiotics compounds in experimental studies. This investigation presents a reliable indicator of the aquatic ecosystem contamination and the possible negative impact of the surrounding environment.

Key words: Environmental pollution, Heavymetals, Histopathology,Common carp,Cyprinuscarpio L

INTRODUCTION

Marine environments near industrial and urban centers are contaminated with a wide range of chemicals that may be transformed into new potentially toxic compounds. The environmental conditions are not static and human influence has greatly stimulated the flow of environmentally deleterious changes by loading with chemicals to the aquatic system. The heavy metal and pesticide contamination of aquatic system has attracted the attention of researchers all over the world (Dutta and Dalal, 2008). In the last few decades thousands of organic trace pollutants are released into the environment (Vander Oost, et al., 2003). Heavy metals cannot be destroyed through biological degradation. When exposed to higher concentrations, organs of aquatic animals may accumulate heavy metals (Pelgrom et al., 1995, Grosell et al., 1996, Kalay et al., 1999, Mazon et al., 2002 and Ashraf, 2005). Heavy metals accumulated in the tissues of fish catalyze redox reactions that generate reactive oxygen species (ROS) which may lead to environmental oxidative stress and, therefore, cause biochemical and morphological alterations in fish (Varanka et al., 2001 and Monteiro et al., 2005). There is a positive link between the presence of certain xenobiotics in water and sediments which onset the sublethal effects in resident fish species in aquatic bodies. The xenobiotics initiate a specific enzyme that alters metabolism by cellular intoxication at cellular level and necrosis on a tissue level. Among the aquatic species the fishes are the major targets of heavy metal contamination.

Fishes come into contact with multiple metal contaminants in the aquatic environment and biomagnifies the pollutants. These pollutants built up in the food chain are responsible for adverse effects and death in the aquatic organisms (Farkas et al., 2002). Fish are largely being used for the assessment of the quality of aquatic environment and as such can serve as bioindicators of environmental pollution (Lopes et al., 2001, Whitefield and Elliott, 2002 and Dautremepuits et al., 2004).

Heavy metals undergo metabolic activation that provokes a cellular change in the affected fish. The tissue lesions and apoptosis arise from bioaccumulation, infections, diseases and parasites stimulate necrotic alterations in the fish with an inflammatory defensive reaction (Roganovic – Zafirova et al., 2003). It is imperative that histological biomarkers are the indicators of pollutants in the overall health of the entire population in the ecosystem (Velkova – Jordanoska and Kostoski, 2005). Well documented reports can be found in organs of fish exposed to heavy metals, chemical pollutants and microorganisms (Adham et al., 2002, Olojo et al., 2005, Roganovic – Zafirova and Jordanova, 1998 and Farombi et al., 2007).The freshwater fish, common carp (Cyprinus carpio L.) is of great commercial importance because it is the most common fish widely consumed worldwide. Therefore, it can be a good model to study the responses to various environmental contaminations. The investigation of histological changes in organs of fish is an accurate way to assess the effects of xenobiotics compounds in experimental studies. Hence, this study was undertaken to examine the effect of different heavy metals at sublethal concentrations on histology of gills, liver, kidney and flesh of common carp (Cyprinus carpio L.). This investigation presents a reliable indicator of the aquatic ecosystem contamination and the possible negative impact of the surrounding environment.

MATERIALS & METHODS

The freshwater Cyprinus carpio L. (Common carp) (10 – 13 cm length and 35.70 ± 0.60g) was collected from ponds of southern districts of Tamilnadu, India and was acclimated to laboratory conditions for a week. Twenty to twenty five individuals were used for the experiments. All the fish were kept in batches under constant temperature (25 ± 1°C) with a controlled photoperiod of 12:12 hour light and dark cycle and constant filtration. Analytical grade cadmium chloride, lead nitrate, potassium chromate and nickel sulphate supplied by BDH (India) were used as metal toxicant through out the experiment. The fish used for this experiment were maintained in 200L recirculating tanks, filled with dechlorinated tap water. The physico chemical characteristics of tap water were presented in (Table 1). The water in the control and experimental tanks was changed for every 3 days. The fish were divided into two groups, with the first group serves as control and remaining as experimental group. The experimental group was exposed to a sublethal concentration of 5 mg/L of combined (Cd + Pb + Cr + Ni) metal solution containing 1.25 mg/L of each metal ion (1/10^th of LC50 / 48h) for a period of 32 days. The heavy metal concentrations were selected based on preliminary results, shown to be sublethal after a 32 day period of exposure. No fish mortality was observed during the experiment.

The fish was fed with commercially available fish feeds at a daily rate of 3 – 4 % body weight through out the experiment. The fish were starved for 24 hours before experimentation. After dissection at least five sampled pieces of gills, liver, kidney and flesh were collected per fish (making a representative sample of the entire organ). A gill arch of the right side of each fish, liver, kidney and flesh samples were collected and fixed in 10% formalin for 24h, dehydrated in graded ethanol concentrations and embedded in paraffin wax. Sagittal sections (5μm of thickness) were cut and mounted on glass slides. Sections were deparaffinized in xylene, hydrated in ethanol and stained with hematoxylin – eosin (HE) method and approximately 2 – 4 sections of each individual fish were analyzed by light microscope.

RESULTS & DISCUSSION

The gill morphology of control common carp (Cyprinus carpio L.) remains an ordinary structure in which lamellae are lined by squamous epithelium composed of non differentiated cells (Fig. 1). The gill of heavy metal exposed group show some epithelial lesions when exposed to heavy metals. The filament region constitutes edema with intense lamellar vasodilatation. The gills exhibit a stratified fusion of pigments in numerous spaces are found in the gill of heavy metal exposed common carp (Fig. 2).

The liver sections of control hepatocytes exhibit a normal structure with no abnormalities in the hepatocytes. It exhibits a homogenous cytoplasm around the centrally located spherical nucleus (Fig. 3). The hepatic tissues of common carp pronounced pathological changes after 32 days of exposure exhibit a marked cytoplasmic vacuolization. The presence of hemosiderin a product of hemoglobin degradation (Khan et al., 1994) results in internal bleeding in the liver tissues of common carp. The interruption of blood sinusoids separates the hepatic cords and the cells lost its normal size, number and structure. Liver parenchyma cells depict the accumulation of macrophages contained lipofusin pigments indicate the reaction of malondialdehyde in oxidative stress developed by heavy metals. The cells show an intrusion of fatty degeneration with liver fibrosis caused by infiltration of collagen fibers in the hepatocytes of common carp (Fig. 4).

The section of control kidney tissues exhibits an ordinary pattern with no abnormal changes in the cells (Fig. 5). There was an increased activity of connective tissues, particularly near the kidney tract. The circulatory disorders and numerous macrophages and inflammatory cells develop necrosis around the border of tissues changed the normal shape of kidney with a dislocation of epithelial cells were found in fish from a chronic toxicity of heavy metals. A selective dystrophic change in kidney tubules together with hyper secretion of mucous cells in the affected region showing atrophy in the underlying tissue was observed in heavy metal intoxicated groups. The pronounced activity of macrophages and large eosinophilous cells with granulated cytoplasm in the sub mucosa of gut wall in the kidney tubules showed a diminished appearance revealed the long term effect of heavy metals in the kidney of common carp tissues (Fig. 6).

The flesh samples of control fish shows a normal appearance (Fig. 7). In case experimental fish, a severe regressive changes in flesh samples was accompanied with the spread of tissue injury. The toxicity in the flesh samples are characterized by disappearance of striations. The tissues involved in necrosis with a homogenous liquid appearance and loss of staining properties. Enlarge lesions in epidermis completely changed the architecture of external cell layer. A granulomatous lesion observed in the tissues was totally damaged proceeding to hyperplasia in cells (Fig. 8).The fish exposed to heavy metals reflect several histological alterations. The gills of control fish show a regular structural organization of the lamellae. The fish exposed to heavy metals dispute changes in histology with proliferation of epithelial cells, fusion and degenerative changes in the lamellae. Lesions are found in the target cells with the accumulation of edema. Several earlier studies reported that edema with frequent lesions in gill epithelium of fish exposed to heavy metals (Mallatt, 1985) specifically cadmium (Reid and Mc Donald, 1988) and nickel (Pane et al., 2004). Thehigher accumulationoflead, cadmium, chromium and nickel induce lipid peroxidtion and biochemical alteration in the antioxidant enzymes could be toxic mechanism in the organs of exposed fish. The gills serve as a respiratory organ in fishes that has direct contact with water. The metals penetrate the epithelium of gills and develop oxidative stress in cells. It was found that heavy metals accumulatedintheliver, kidney,heartandgillsinduce oxidative stress in fish (Farombi, 2007 and Oakes and Vander Kraak, 2003). The lesions found in gill structure can change the normal structure and function of cells. The present findings reflect similar trend in cadmium exposure to gills induce lesions in gill epithelium (Thophon et al., 2003).

The liver of control fish provides normal structure with no pathomorphological abnormalities. A homogenous cytoplasm with a large central spherical nucleus is the characteristic nature of control hepatocytes. The histology of heavy metal exposed liver caused a reduction in size and shape of nucleus with degenerative changes in parenchyma cells with necrosis and apoptosis. The decrease number of nucleus in the hepatic tissues was reported in copper exposed to Oreochromis niloticus (Figueiredo, 2007). The concentration of heavy metals create an adduct in the liver cells due to their metal chelating proteins that target the cells to release lipofuscin an end product of lipid peroxidation and pigment hemosiderin as a result of internal bleeding in the hepatic tissue of Cyprinus carpio. The higher accumulation of combined heavy metals in liver support other work of lead accumulation in the liver (Kargin and Cogun, 1999) and cadmium in liver (Kalay et al., 1999). The characteristic appearance of liver fibrosis in the heavy metal exposed fish was supported by report of sunfish in Texas reservoir contaminated with selenium enriched power plant (Sorenson, 1988).The higher bioaccumulation of heavy metals in the kidney could be on specific metabolic process. Macrophages are key cells present in kidney dealing with foreign material and cellular debris (Blazer et al., 1944 and Evans, 1998). The macrophages constitute lipofuscin, melanin and hemosiderin pigments. The present study revealed the presence of hemosiderin pigment in the heavy metal intoxicated kidney tissues supported by exogenous environmental factors like contaminants influence macrophage pigment composition (Blazer et al., 1994 and Kruger et al., 1996).The tissues in flesh samples of intoxicated group show damaged structure with the invasion of cytoplasm. The lesions on the exposed group in turn cause muscle destruction. The affected flesh region arise giant granulomas that undergone necrotic changes in the tissues of heavy metal exposed fish. The present investigation was supported by Kabata arthuri infection in muscle fibres of sutchi cat fish, Pfangasius sutchi (Dykova, 2000).

CONCLUSION

Histopathological alterations in common carp under the influence of heavy metals can be used as a sensitive model to monitor the aquatic pollution. The current result indicates that the heavy metal contamination definitely affect the gills by proliferation of epithelial cells and accumulation of edema in the target cells. Liver tissue generates hemosiderin and cytoplasmic vacuolization as a result of metal toxicity. Aggressive invasion of macrophages and giant granulomas observed in the kidney and flesh tissues were the characteristic changes at the cellular level of fresh water fish. Hence, a scientific method of detoxification is essential to improve the health of these economic fish. The present research work served as an experimental tools and bioindicators for the first line evaluation of environmental pollution.

ACKNOWLEDGEMENT

The authors wish to thank our college Principal Rev. Dr. Alphonse Manickam SJ and Prof. M.Thomas Punithan, Head of the Department of Advanced Zoology and Biotechnology, St. Xavier’s College (Autonomous), Palayamkottai, Tamilnadu, India, for their kind encouragement and their laboratory facilities. This paper forms a part of the Ph.D thesis submitted by R.Vinodhini to M.S. University, Tirunelveli, Tamilnadu, India.

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