x Present address: (mallesh.aem08@cife.edu.in). The chromium is recognized as a heavy metal, which is known to be toxic to fish and the human beings The toxicity of chromium to aquatic life is strongly influenced by the chemical speciation of chromium and water quality (Abbasi and Soni, 1985) and considerably varies between and within groups of organisms. Growing awareness about aquatic pollutants generating potential hazards has stimulated much interest in the use of fishes as indicators for monitoring the environmental mutagens, carcinogens and teratogens (Krishnaja and Rege 1982). Fishes are ideal indicators of heavy metal contamination in aquatic ecosystems and these are unique among the vertebrates, because of the potential for metal acquisition from the water. Contamination in the aquatic environment alters their health, size, age structure, composition and number of species found in the aquatic ecosystem. Some heavy metals accumulate in tissues and may pose a health risk to those who frequently consume fish. Chromium (Cr) has a role in glucose, fat and protein metabolism, participating in the insulin action (Anderson 1981). It links directly to macromolecules; fragments the AND (acridinium ditetracyanoquinodimethane) chains and acts in the peroxidation of lipids, generating free radicals and modifying the routes of cell signals. All these processes can contribute to the toxicity and carcinogenicity of Cr compounds (Loyaux Lawniczak et al. 2000). Many studies have been carried out to evaluate the extent of genetic disorders caused by heavy metals in the fish and developed several techniques to evaluate the genotoxic effect of heavy metals in the organism using a variety of genetic end-points. Micronucleus assays originally developed with mammalian species have been used extensively to test for the genotoxic activity of chemicals (Heddle et al . 1983). Micronuclei are formed by condensation of chromosomal fragments or whole chromosomes that are not included in the main nucleus following anaphase. Scoring of micronuclei in the interphase is technically much easier and more rapid than the scoring of chromosomal aberrations during metaphase. The micronucleus (MN) (MNi) test in fish also has potential for detecting clastogenic substances in aqueous media. Since teleost erythrocytes are nucleated, micronuclei have been scored in fish erythrocytes as a measure of clastogenic activity. The study was carried out to determine the LC 50 value of Cr in Cirrhinus mrigala to analyse the impact of chromium on acute static bioassay of C. mrigala, which is prerequisite to determine the degree of damage produced by chromium. Hence, the study was carried out to measure the bioconcentration of chromium in C. mrigala, and to evaluate the genotoxic effect of chromium in C. mrigala. MATERIAL AND METHODS The study was conducted in wet lab facility of Central Institute of Fisheries Education (CIFE), Mumbai located at latitude 18° 55’N and longitude 72° 50’E. Analytical grade potassium dichromate (K 2 Cr 2 0 7 ) was used as the source of chromium in the experiment. A subchronic Indian Journal of Animal Sciences 85 (5): 92–00, May 2015/Article Bioconcentration of hexavalent chromium in different organs and induction of micronuclei in peripheral blood cells of Cirrhinus mrigala (Ham, 1822) B MALLESH 1 , P K PANDEY 2 , KUNDAN KUMAR 3 , A VENNILA 4 , S P SHUKLA 5 , R P RAMAN 6 and SAURAV KUMAR 7 Central Institute of Fisheries Education, Versova, Mumbai, Maharashtra 400 061 India Received: 28 April 2012; Accepted: 19 November 2014 ABSTRACT The fingerlings of Cirrhinus mrigala (Ham, 1822) were exposed to different concentrations of chromium in the form of K 2 Cr 2 O 7 . LC 50 for 96 hours was calculated as 52.187 mg L –1 . For sub-lethal toxicity test fishes were exposed to different concentrations of 10.437, 5.218 and 3.479 mg L –1 for 60 days. In comparison to control under the same conditions, the experimental fish showed remarkable change in the accumulation pattern in muscle, gills and liver. The Cr content was measured using Atomic Absorption Spectrophotometer (AAS) and the highest concentration was found in liver (61.91±0.73 μg g –1 ) followed by gills (16.67±0.08 μg g –1 ) and muscle (8.97±0.06 μg g –1 ). Frequencies of micronuclei were evaluated in peripheral blood erythrocytes. Cells showed differential sensitivity to the heavy metal treatment. In general, frequencies of MNi cells significantly increased following the exposure for 60 days to chromium. Frequencies of micronuclei formation in erythrocytes varied from (0.83±0.06%) to (6.37±0.56%). The results indicated that this heavy metal has genotoxic effects in the fish. Key words: Bioassay tests, Bioconcentration, Chromium, Cirrhinus mrigala, LC 50 , Micronucleus test