Inter-Research > DAO > v100 > n3 > p219-230  
Diseases of Aquatic Organisms

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DAO 100:219-230 (2012)  -  DOI:

New pathological condition in cultured mulloway Argyrosomus japonicus: histopathological, ultrastructural and molecular studies

Dina Zilberg1, J. Brian Jones2, Mieke A. A. Burger2, Philip K. Nicholls3, Druime Nolan2, Melanie Crockford2, Fran Stephens2,*

1French Associates Institute for Agriculture and Biotechnology of Drylands, Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben Gurion 84990, Israel
2Fish Health Laboratory, Department of Fisheries, Government of, North Beach, Western Australia 6020, Australia
3School of Veterinary and Biomedical Sciences, Murdoch University, Murdoch, Western Australia 6150, Australia
*Corresponding author. Email:

ABSTRACT: Mulloway Argyrosomus japonicus is a native fish species in Western Australia, for which aquaculture production has recently been developed. A single cohort was stocked in a cage offshore at Geraldton, Western Australia, at a water depth of 6 m. Fish appeared healthy before stocking. Routine histological analysis was carried out from 10 mo post stocking and until completion of harvest (about 2.5 yr post stocking). No gross pathology was evident. Microscopically, however, granulomatous lesions were present in the kidneys of almost 100% of the fish examined. Enclosed in the granuloma was an aggregate of organisms, 4.2 to 5.4 µm in diameter. Kidney granulomas appeared as multi-focal aggregates. Granulomas at different stages of formation and finally fibrosing granulomas were observed. Granulomas also appeared infrequently in other organs: a few granulomas were found in the liver and spleen and a single granuloma in the heart of one fish. Transmission electron microscopy (TEM) revealed that the organism was composed of 2 cells, an outer cell enclosing an inner cell. The inner cell was surrounded by a double membrane and the outer cell by a single membrane. Cellular material, presumably of parasitic nature, surrounded the outer cell. The organism contained primitive mitochondria and abundant free ribosomes. Small subunit ribosomal DNA (SSU rDNA) sequence obtained by PCR revealed an 84% sequence identity with the myxosporean Latyspora scomberomori. Based on TEM and preliminary molecular results, we suggest that the organism is the extrasporogonic developmental stage of a myxozoan parasite, which failed to form spores in the mulloway host.

KEY WORDS: Granuloma · Parasite · Mulloway · Liver · Fish

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Cite this article as: Zilberg D, Jones JB, Burger MAA, Nicholls PK, Nolan D, Crockford M, Stephens F (2012) New pathological condition in cultured mulloway Argyrosomus japonicus: histopathological, ultrastructural and molecular studies. Dis Aquat Org 100:219-230.

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