Individuals of both sexes were presented with potential mating partners of different sizes. Mating preferences were quantified in terms of time spent courting each potential partner.

Mattle and Wilson found striking differences in courtship behaviour between male and female sea-horses, with choosy males and indiscriminate females, said a University of Zurich release.

Male sea-horses were highly active and showed a clear preference for larger partners. In contrast, females were significantly less active and showed ambiguous mating preferences.

The authors concluded: 'The strong male preferences for large females demonstrated here suggest that sexual selection may act strongly on female body size in wild populations of H. abdominalis, consistent with predictions on the importance of female body size for reproductive output in this species.'

Their findings were published online in the journal Behavioural Ecology and Socio-biology.