We studied the association between environmental stress and epidermal papillomatosis of roach Rutilus rutilus L. in Finnish waters using a 'matched pairs' design. Populations impacted by industrial and/or sewage effluents were compared to reference populations from pristine sites. We examined both the prevalence (proportion of diseased fish) and intensity (number of scales covered by tumors) of the disease. Results of Generalized Linear Mixed Models (GLMM) indicated that the risk of papillomatosis was 7.5 times higher in males than females, and increased 1.3 times for every 10 mm increment in fish length. We controlled for the possible effects of fish size, sex and temporal variation through sampling procedures and statistical analyses. Mean prevalence of epidermal papillomatosis was 16.6 and 5.8% in impact and reference populations, respectively (10 population pairs; n fish = 1714). Results of GLMM suggested that the risk of being diseased was 2.7 times higher in the impact than reference populations. Thus, the prevalence of epidermal papillomatosis in roach can be used as an indicator of environmental stress. Results of Linear Mixed Models indicated no difference in the intensity of the disease between impact and reference populations (5 population pairs; n fish = 73; mean ± SE 10.7 ± 1.8 and 11.7 ± 2.9 scales, respectively), although prevalence was higher in impact populations in those 5 population pairs. The possible relationship between environmental stress and intensity of epidermal papillomatosis in natural roach populations remains to be demonstrated. KEY WORDS: Environmental monitoring · Epizootic cutaneous papillomatosis · Roach · Disease · Large lakes · Matched pairs Resale or republication not permitted without written consent of the publisherDis Aquat Org 72: [1][2][3][4][5][6][7][8] 2006 and by isolation from cell culture (Schwanz-Pfitzner 1976, Bloch et al. 1986, Sano et al. 1993. However, induction of papillomas can possibly also take place without viral infection (e.g. Grizzle et al. 1984, Smith et al. 1989a). Thus, the connection between papillomatosis and environmental stress can be produced both by the stress induced impairment of the immune system of fishes and by direct carcinogenic effects of contaminants (Sano et al. 1991, 1993Lee & Whitfield 1992, Baumann et al. 1996.In the North American Great Lakes, epidermal papillomatosis has been proposed as a bioindicator of contaminated waters (Munkittrick & Dixon 1989, Baumann 1992, Premdas et al. 1995, Baumann et al. 1996. The International Council for the Exploration of the Sea (ICES) has adopted epidermal papillomatosis in dab Limanda limanda as an indicator of environmental changes in the North Atlantic coastal areas (Bucke et al. 1996). Because new tools are required by the European Union's Water Framework Directive for determining the ecological status of lakes, we investigated the possible use of the roach-papillomatosis system in monitoring of environmental stress in Finnish waters.In contrast to prevalence, the intensity of ...

Hypoxia, which occurs frequently in aquatic ecosystems and is mainly due to increasing eutrophication can cause severe environmental stress in fish. We investigated experimentally the hypothesis that hypoxia could be one of the environmental stress factors that can induce papillomatosis in fish. Male roach Rutilus rutilus exposed to periodic oxygen deficiency and accompanied temperature increases (OT group) showed the highest increase in the intensity of papillomatosis, as measured by the number of scales covered by papillomatosis tumors. The second highest increase in disease intensity was among male roach exposed to periodical temperature increases. The incidence of such tumors was lowest in the control group, which was exposed to neither hypoxia nor increased temperature. The mortality of fish during the 17 d experiment was highest and the condition factor was lowest in the OT group, indicating this group experienced a higher level of stress. The apparent interaction of hypoxia and temperature suggests that these environmental stressors are among the multifactorial elements leading to papillomatosis in roach. Furthermore, these results provide experimental evidence to indicate that hypoxia may contribute to tumor development in fish. KEY WORDS: Epidermal papillomatosis · Oxygen deficiency · Temperature · Environmental stress · Disease intensity · Fish Resale or republication not permitted without written consent of the publisherDis Aquat Org 78: [235][236][237][238][239][240][241] 2008 spread distribution of the roach makes it a good indicator species for detection of environmental stressors by the monitoring of the roach-papillomatosis system.In addition to environmental stress, the natural hormonal cycles could impair the immune system of fish (Pickering 1986, Watanuki et al. 2002 and thereby affect papillomatosis. Premdas et al. (2001) also showed that hormonal manipulations affect the development of papillomatosis. Papillomatosis in roach peaks during spawning in spring (Kortet et al. 2002, Vainikka et al. 2004a), a time when concentrations of the stress hormone cortisol are elevated (Vainikka et al. 2004a), sex hormone concentrations change (Kestemont et al. 1999, Kortet et al. 2003b, Vainikka et al. 2004b, and immune functions could be suppressed (Kortet et al. 2003a, Vainikka et al. 2004b. By spawning in shallow backwaters, roach are more susceptible to stressors such as solar radiation and high or variable temperature. Moreover, roach have a lek-like mating system (Wedekind 1996, Kortet et al. 2004, which might further induce stress through crowding and social interactions (e.g. Barcellos et al. 1999). All these factors can result in stress for roach in spring.The aim of this research was to determine the effect of oxygen deficiency on the development of epidermal papillomatosis in roach. Due to the lower oxygen content of water and higher metabolic activity of fish in higher temperatures, we included temperature treatment as a variable in the oxygen deficiency experiment. In addition, we...