DAO 66:1-7 (2005)  -  doi:10.3354/dao066001

Spinal curvature of cultured Japanese mackerel Scomber japonicus associated with a brain myxosporean, Myxobolus acanthogobii

Hiroshi Yokoyama1,*, Mark A. Freeman2, Naoki Itoh3, Yutaka Fukuda4

1Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo,Bunkyo, Tokyo 113-8657, Japan
2Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, UK
3Department of Veterinary Science, Louisiana State University, Baton Rouge, Louisiana 70803, USA
4Oita Institute of Marine and Fisheries Science, Kamiura, Oita 879-2602, Japan

ABSTRACT: Skeletal deformities were found in the cultured Japanese mackerel Scomber japonicus. External and radiographical observations showed the deformed fish to exhibit a dorso-ventral spinal curvature (kyphosis) without fracture or dislocation of the vertebrae. Numerous myxosporean cysts, ca. 0.3 to 1.0 mm in diameter, formed in the 4th ventricle, the cavity of the optic tectum, the surface of the olfactory lobe and bulb, the optic lobe and the inferior lobe of the brain. Spore morphology and molecular analysis of the small subunit ribosomal RNA gene sequence identified the myxosporean parasite as Myxobolus acanthogobii, a parasite which also causes scoliosis in yellowtail Seriola quinqeradiata. Histopathological observation showed that the myxosporean cysts were encapsulated within the host’s collagenous layer although some had disintegrated to disperse mature spores into the cranial cavity. Occasionally, lymphocytic infiltration and local granulomatous inflammation were found to be associated with spore dispersion.

KEY WORDS: Myxozoa · Myxobolus · Spinal curvature · Parasite · Mackerel · Scomber japonicus

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