DAO prepress abstract  -  doi: 10.3354/dao01909

ABSTRACT: An epidemiological study was carried out to investigate the possible aetiology of squamous cell carcinomas, which occur in a population of rudd, Scardinius erythrophthalmus (L.), from Lough Aderry in south-east Ireland. A total of 1343 rudd were sampled in spring, summer, autumn, and winter from Lough Aderry and two nearby small lakes over two years, 1986 - 1988. Fish were weighed, measured, sexed, aged, and examined for lesions. Water quality parameters and natural radioactivity were assessed as possible influencing factors in the disease. The prevalence of squamous cell carcinoma was 6.1% overall, with no significant difference between the lakes, seasons or years. Both male and female fish were affected, from the age of 1+ to 5+. It is likely that the neoplasm caused premature death, in that no fish of 6+ or 7+ years was found with tumours. The female / male sex ratio of rudd with tumours was higher that of healthy rudd overall, which suggests that males are more susceptible to the neoplasm. Of the parasites observed, Posthodiplostomum cuticola was common, but rarely found in rudd with tumours. Sphaerospora sp.was also common, but not in sufficient densities for statistical inference, and Argulus sp. was present on seven fish. No viral particles were found. Natural radiation levels in the vicinity of the lakes were low. The lakes sampled are in an agricultural catchment, and the waters were eutrophic. While rudd are tolerant, it is likely that environmental conditions were stressful at least some of the time, with possible consequences for the immunocompetence of the rudd. The aetiology of the carcinoma is still unknown, but the possibilities of carcinogenic compounds resulting from the high nutrient levels, or of carcinogenic algal toxins produced during algal blooms, should be examined.