J BIOCHEM MOLECULAR TOXICOLOGY Volume 26, Number 3, 2012 Protective Effect of Selenium Against Mercury-Induced Toxicity on Hematological and Biochemical Parameters of Oreochromis niloticus Hikmet Y. Cogun, 1 ¨ Ozg ¨ ur Fırat, 2 ¨ Ozge Fırat, 3 T¨ uzin A. Y ¨ uzereroˇ glu, 4 G¨ ulbin G¨ ok, 4 Ferit Kargin, 4 and Yasemin K¨ otemen 4 1 Department of Biology, Faculty of Science and Letters, Kilis 7 Aralik University, 79100 Kilis, Turkey; E-mail: hcogun@kilis.edu.tr 2 Department of Biology, Faculty of Science and Letters, Adiyaman University, 02040 Adiyaman, Turkey 3 Vocational School of Kahta, Adiyaman University, 02400 Adiyaman, Turkey 4 Department of Biology, Faculty of Science and Letters, Cukurova University, 01330 Adana, Turkey Received 24 July 2011; revised 27 September 2011; accepted 17 October 2011 ABSTRACT: In this study, to identify mercury (Hg) toxicity and whether selenium (Se) has any role in alle- viation of this toxicity, it was investigated the changes in hematological and serum biochemical parameters of Oreochromis niloticus. Fish were exposed to 0.01 and 0.1 mg/L Hg and 0.01 mg/L Hg + 0.1 mg/L Se and 0.1 mg/L Hg + 1.0 mg/L Se for 7 and 14 days. The exposure of O. niloticus to Hg alone resulted in decreases in red blood cell, white blood cell, hemoglobin, hematocrit values, and cholinesterase activity while it increased in alanine aminotransferase and aspartate aminotrans- ferase activities and cortisol and glucose levels. Se, in combination with Hg, partially or totally caused an alleviation for the toxic effect of Hg on the above mentioned hematological and biochemical parameters. The results of our study showed that Se has a pro- tective effect against toxicity induced by Hg. C  2012 Wiley Periodicals, Inc. J Biochem Mol Toxicol 26:117–122, 2012; View this article online at wileyonlinelibrary.com. DOI 10:1002/jbt.20417 KEYWORDS: Oreochromis niloticus; Mercury; Selenium; Interaction; Blood parameters INTRODUCTION Metals are able to disturb the integrity of the phys- iological and biochemical mechanisms in fish that are not only an important ecosystem component but also Correspondence to: Hikmet Y. Cogun. Contract Grant Sponsor: Kilis 7 Aralık University (Turkey). Contract Grant Number: BAP 200/01. c  2012 Wiley Periodicals, Inc. used as a source of food [1]. Mercury (Hg) is a well- known global contaminant to aquatic species, more specifically in fish and marine mammals [2]. Hg ac- cumulates in many fish species and causes various diseases such as renal [3], hepatic lesions [4], and en- docrine impairment [5]. On the other hand, selenium (Se) is considered as an essential trace element for living organisms. Se can act as a growth factor [6], has pow- erful antioxidant [7] and anticancer [8] properties, and is essential for immunity [9]. Se has also been found to have detoxification effects on various heavy metals [10]. The interactions between the toxicities of Hg and Se are perhaps the best known of all interactions among environmental contaminants [11]. The presence of Se reduced the availability of metal ions [such as Hg and cadmium (Cd)], blocking them in insoluble compounds [12]. Hg selectively binds with selenium to form insol- uble Hg selenides [13]. This interaction has been as- sumed to be a “protective” effect whereby supplemen- tal selenium complexes the Hg and prevents negative effects in animals fed otherwise toxic amounts of Hg [14]. The antagonistic action of Se against the toxic- ity of Hg, which forms in aquatic organisms, has been proposed in the past [15]. Sodium selenite as the chem- ical form of selenium is usually used as an antioxidant because this form is intentionally added in small quan- tities in animal diet to promote good health and also because sodium selenite is known to protect against Hg poisoning [16]. Fish live in very intimate contact with their envi- ronment, and are therefore very susceptible to physical and chemical changes [17]. Since the blood forms a unique compartment between the external and inter- nal environments, agents including metals that cause 117