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Diseases of Aquatic Organisms

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DAO 63:113-118 (2005)  -  doi:10.3354/dao063113

Nodavirus infection causes mortalities in hatchery produced larvae of Lates calcarifer: first report from India

I. S. Azad1,2,*, M. S. Shekhar1, A. R. Thirunavukkarasu1, M. Poornima1, M. Kailasam1, J. J. S. Rajan1, S. A. Ali1, M. Abraham1, P. Ravichandran1

1Central Institute of Brackishwater Aquaculture, 75-Santhome High Road, R. A. Puram, Chennai 600 028, India
2Present address: Aquaculture, Fisheries and Marine Environmental Dept, Kuwait Institute for Science Research,Salmiya 22017, Kuwait

ABSTRACT: Larvae (15 to 21 d post hatch, dph) of the Asian sea bass Lates calcarifer (Bloch) suffered heavy mortalities (60 to 90%) during the hatchery-rearing phase. Darkened and moribund larvae showed no evidence of bacterial or parasitic infections. Tissue sections of brain and spinal cord showed clear necrotic vacuolation. Electron microscopy revealed membrane-bound viral particles in the cytoplasm of the nerve cells. The viral particles measured 28 to 30 nm in diameter. Primer sets, designed for the amplification of the RNA2 segment of the piscine nodavirus coat protein gene, were used in the RT-PCR analysis of moribund larvae of 20 and 21 dph which produced the amplified product of 430 bp. The clinical manifestations, pathology and electron microscopy observations supported by the RT-PCR analysis suggest that the nerve necrosis was due to nodavirus infection in the larvae. This is the first report of piscine nodavirus infection from the Indian sub-continent.

KEY WORDS: Nodavirus · Lates calcarifer · Larvae · RT-PCR · Histopathology · Nervous necrosis virus

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