Epizootic cutaneous papillomatosis, cortisol and male ornamentation during and after breeding in the roach Rutilus rutilus

The prevalence of epidermal papillomatosis in roach is known to peak during the spawning period and to be higher in males than in females. The high occurrence of papillomatosis in polluted waters suggests that stress may contribute to the outbreak of the disease. However, little is known about breeding-induced stress in fish and its relationship with diseases. In this study, plasma cortisol concentration, hematocrit and the relative size of the spleen were determined in healthy and diseased male and female roach Rutilus rutilus during and shortly after spawning in a wild population. In addition, the sexual ornamentation (breeding tubercles on the lateral sides and on the frontal) of male roach during spawning was examined. Plasma cortisol concentration was higher during than after the spawning period, and higher in males than in females during spawning, indicating a spawning-induced stress and higher spawning stress among males. There was no correlation between cortisol concentration and the intensity of papillomatosis (number of scales under papilloma tumors) among the diseased fish. However, the significant interaction sex x disease status revealed by ANCOVA suggested that diseased males could be more prone to increased cortisol levels than diseased females or healthy males. Hematocrit values (ratio of the volume of red blood cells to total volume of blood) but not condition factor were lowered in papilloma-diseased fish after spawning. The relative size of the spleen was greater in males than in females. The number of frontal breeding tubercles correlated negatively with the intensity of papillomatosis. Experimental studies are needed to investigate the association of papillomatosis with stress and cortisol.