Sex differences in the responses to oviposition site cues by a fish revealed by tests with an artificial host

Oviposition decisions can have important fitness consequences for offspring. We investigated the responses of European bitterling, Rhodeus amarus, a freshwater fish that spawns in the gills of living unionid mussels, to oviposition site cues. Using an artificial mussel, we manipulated the flow velocity, dissolved oxygen concentration and odour cues of mussels presented to pairs of R. amarus. Females responded positively to mussel odour and to dissolved oxygen cues. Male response was dependent on mussel odour and the flow velocity of water emerging from the artificial mussel. These responses are potentially adaptive, with females responding to cues that indicate the quality of oviposition sites for incubation of eggs. Males responded to cues with implications for optimal sperm allocation.