• Coregonus lavaretus;
  • fitness;
  • maternal effect;
  • offspring performance;
  • paternal effect;
  • secondary sexual characters;
  • sexual selection

Mutual ornamentation (i.e. the expression of secondary sexual characters) in both sexes is a relatively common but rarely studied phenomenon in the animal kingdom. In the present study, we investigated whether mutual ornamentation is indicative of offspring embryonic survival and predator-avoidance ability in whitefish. We crossed ten randomly selected females and ten randomly selected males in all possible combinations resulting in 100 sib groups, and hypothesized that fitness (measured as offspring survival) of elaborately ornamented parents would be higher in both sexes of whitefish. Parental effects were found in both studied traits: effects of female and female–male interaction were significant for the embryonic mortality, whereas only paternal effect was found for the offspring predator-avoidance ability. As expected, increasing number of the female breeding tubercles was associated with low embryonic mortality, although male ornamentation was not indicative of offspring survival. The present study, together with earlier data, clearly demonstrate that offspring fitness is affected by parental identity, and suggest that mutual ornamentation in this species may indicate the genetic quality of individuals in both sexes. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 593–601.