Sex and sexual ornamentation associated with survival of the cyprinid fish, Rutilus rutilus, under disease stress

By conveying information of disease resistance, sexual signals may be used as cues for adaptive mate choice. Here we report observations on survival of laboratory-maintained, wild-collected, sexually mature, ready-to-spawn cyprinid fish, Rutilus rutilus (roach), under accidental epidemic attributed to Flavobacterium psychrophilum, diagnosed using species-specific PCR. The fish were maintained in a single tank. During the 27 days observation period, both the proportion of fish surviving the infection as well as the length-adjusted mean survival time of the fish that died was the highest among the high-ornamented males with large breeding tubercles, intermediary among the low-ornamented males with small or no breeding tubercles, and the lowest in females. Control fish in another tank did not show disease symptoms and experienced 100% survival. It should be noticed that this was not an experiment designed to study the survival question—the fish were in storage tanks to be used for other purposes. However, in line with earlier studies on the association between breeding tubercles and parasite resistance in R. rutilus, the present observations suggest that the sexual signals of roach may be indicators of survival under disease stress.