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Diseases of Aquatic Organisms

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DAO 103:25-34 (2013)  -  DOI:

Hyperpigmentation in North Sea dab Limanda limanda. II. Macroscopic and microscopic characteristics and pathogen screening

P. A. Noguera1,*, S. W. Feist2, K. S. Bateman2, T. Lang3, F. Grütjen3, D. W. Bruno

1Marine Scotland Science, 375 Victoria Road, Aberdeen AB11 9DB, UK
2Cefas Weymouth Laboratory, Barrack Road, Weymouth DT4 8UB, UK
3Thünen Institute of Fisheries Ecology, Deichstr. 12, 27472 Cuxhaven, Germany

ABSTRACT: An increasing trend in the prevalence of hyperpigmentation in the common dab Limanda limanda from the North Sea prompted us to investigate the potential role of infectious agents as causes or contributing factors to the condition. Dab representing 3 severity grades of hyperpigmentation were sampled for virology, bacteriology, histopathology and ultrastructure assessments. No cytopathic effect was recorded during virology testing, and bacteriological results showed no differences between normal and hyperpigmented dab. Histopathological assessment showed that the most significant changes occurred in the dermis as a result of chromatophore hyperplasia, namely melanophores and iridophores, alongside loose melanin granules. Dermal lymphocytic infiltration occasionally expanding into the epidermis and the underlying musculature was more frequent in highly pigmented dab than in normal fish, suggesting an active immune response. Ultrastructure studies showed additional disruption of the epithelial layer, with loose melanin granules between cells and a number of single or aggregated melanocytes. Dab representing different grades of hyperpigmentation kept in the laboratory alongside normal fish for a monitoring period of 18 mo showed no changes in their pigment distribution pattern, nor occurrence of new pigment in the normal fish. The current investigation found no association of hyperpigmentation in the common dab with infectious agents; therefore, understanding the cause of the condition remains a challenge which can now more reliably focus on a non-infectious origin hypothesis.

KEY WORDS: Common dab · Flatfish · Pigment anomaly · Chromatophores · Hyperplasia

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Cite this article as: Noguera PA, Feist SW, Bateman KS, Lang T, Grütjen F, Bruno DW (2013) Hyperpigmentation in North Sea dab Limanda limanda. II. Macroscopic and microscopic characteristics and pathogen screening. Dis Aquat Org 103:25-34.

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