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

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.

Hyperpigmentation in North Sea dab Limanda limanda. I. Spatial and temporal patterns and host effects

“…Noguera et al (2013) addresses macroscopic and microscopic characteristics of the condition as well as results from virological and bacteriological testing of the involvement of pathogens as aetiological factors.…”

“…Pigment anomalies of some other flatfish species are well documented and have been described to affect wild populations (De Veen 1969, Gartner 1986, Macieira et al 2006 as well as farmed fish (Ottesen & Strand 1996, Venizelos & Benetti 1999, Bolker & Hill 2000, Copeman & Parrish 2002, Bolker et al 2005, Yamanome et al 2005, Noguera et al 2013. However, hyperpigmentation observed in dab may be a distinct phenomenon and differs from other types recorded because of its high prevalence and cellular and tissue characteristics (Noguera et al 2013).…”

“…Data are available for the North Sea and adjacent waters such as the English Channel, Irish Sea, Celtic Sea and North Scottish waters (Cefas 2009, Noguera et al 2013.…”

“…For this purpose, we used data obtained in fish disease monitoring programmes carried out by Germany and the UK (England and Scotland). In an additional contribution on this topic, Noguera et al (2013) provide information on macroscopic, histological and ultrastructural characteristics of the phenomenon as well as on the involvement of pathogens.…”

Malpigmentation in <i>Diagramma pictum</i> and <i>Pardachirus marmoratus</i> Collected from the Arabian Sea Coasts of Oman

“…On the other hand, hyperpigmentation in teleost fishes can cause melanophore hyperplasia. Such an effect has been stated previously in a number of fish species (Noguera et al, 2013;Ramos et al, 2013).…”