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Diseases of Aquatic Organisms

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DAO 68:189-196 (2006)  -  doi:10.3354/dao068189

Immune response and disease resistance of Oreochromis mossambicus to Aeromonas hydrophila after exposure to hexavalent chromium

M. Prabakaran1, C. Binuramesh1, D. Steinhagen2, R. D. Michael1,*

1Centre for Fish Immunology, Postgraduate and Research Department of Zoology, Lady Doak College, Madurai 625002, Tamil Nadu, India
2Fish Disease Research Unit, Centre for Infection Medicine, School of Veterinary Medicine, Bünteweg 17, 30559 Hannover, Germany
*Corresponding author. Email:

ABSTRACT: The objective of this study was to investigate the effect of chronic exposure to sublethal concentrations of hexavalent chromium (K2Cr2O7) on the immune response and disease resistance of Oreochromis mossambicus (Peters) to bacterial Aeromonas hydrophila infection. Fish (45 to 50 g) were exposed to 0.005, 0.05, 0.5, and 5 mg l–1 [0.01, 0.1, 1, and 10% LC50, respectively] of hexavalent chromium Cr (VI) for 28 d. The specific immune response was assessed by antibody response to A. hydrophila by bacterial agglutination assay, and to sheep red blood cells (SRBC) by plaque forming cell (PFC) assay. In addition, nonspecific immune mechanisms were assessed by serum lysozyme activity and reactive nitrogen intermediates, the latter in terms of nitric oxide (NO) production by peripheral blood leucocytes. Overall immunity was assessed by disease resistance against live virulent A. hydrophila. The study clearly indicated that chronic exposure of fish to 0.5 and 5 mg l–1 of chromium (VI) decreased both nonspecific and specific parameters of the immune system, which resulted in a lower disease resistance to A. hydrophila. Interestingly, 0.05 mg l–1 of Cr (VI) enhanced disease resistance and both nonspecific and specific immune responses to A. hydrophila. Our study revealed a concentration-dependent modulation of the immune system by chromium (VI), as demonstrated by suppressive or stimulatory effects on lymphocytes, lysozyme, phagocytic killing mechanisms, and disease resistance in O. mossambicus.

KEY WORDS: Chromium · Exposure · Disease resistance · Lysozyme · Nitric oxide · Oreochromis mossambicus · Antibody response

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