The skin response of fish to ultraviolet radiation : a histological study

Abstract

A histological investigation of the effects of ultraviolet (UV) radiation upon the skin of four species of teleost fish was conducted in an attempt to define the sequential pathogenesis of the UV induced lesion. The species used in the experiments, namely plaice Pleuronectes platessa L., turbot Scophthalmus znax.zmus (L.), rainbow trout, Sairno gairdneri Richardson and Atlantic salmon, Salrno salar L. represent species reared commercially and thus likely, in the artificial environment of a fish farm, to receive levels of solar radiation in excess of those encountered in nature. It was found that plaice were the most susceptible species to UV radiation whilst turbot were marginally less so. Rainbow trout and Atlantic salmon showed similar levels of susceptibility when compared with each other but, in addition, had significantly higher tolerance thresholds than either plaice or turbot. Whilst the use of artificial radiation sources allows for more accurate control over irradiance than would natural sunlight, the need to recognise the limitations of such sources has been emphasised. In addition the importance of incorporating filters to remove the shorter wavelengths which would not be encountered at the earth's surface has been demonstrated. The photoreactive capability/capability of fish skin to repair cell damage initiated by UV radiation has been shown by the use of variable light input in the visible spectrum. The use of scanning electron microscopy to examine the surface topography of the radiation lesion confirmed the observations made by light microscopy and demonstrated the vulnerability of the damaged skin surface to the invasion of opportunistic bacteria. The importance of recognising sunlight as an environmental factor in the initiation of dorsal skin damage is no longer in doubt; experimental evidence and clinical observations on high altitude fish farms confirm this. Consideration is also given to the implications of prolonged exposure to sunlight upon fish following transfer and handling. The possible role of sunlight in the aetiology of certain bacterial skin diseases in farmed and wild fish and in dorsal skin neoplasms in wild fish is discussed.