Mussel ventilation rates as a proximate cue for host selection by bitterling, Rhodeus sericeus

A range of cues may be used by parasites in selecting hosts, yet few studies have examined multiple cues simultaneously. We investigated the proximate cues involved in spawning decisions of the European bitterling, Rhodeus sericeus, a species of fish which lays its eggs in four species of freshwater mussel. When offered a choice of both live and artificial mussels within a single species, females preferred mussels that have high flow speeds and that pump a large volume of water per unit time. Furthermore, the time taken to spawn for a second time in a mussel was accurately predicted from a mussel's ventilation rate. These bitterling preferences based on mussel ventilation rates may benefit the embryos through enhanced oxygenation. We found no preferences for mussel species based on visual or olfactory cues, though the latter cannot be ruled out entirely. Ventilation rates should indicate the quality of host species for offspring survival.