Nonselective use of vegetation for spawning by the diadromous fish Galaxias maculatus

Abstract

Terrestrial egg development is advantageous for the amphidromous fish Galaxias maculatus because it increases access to oxygen, increases incubation temperatures, and reduces aquatic predation. The characteristics of New Zealand's riparian vegetation have changed considerably since colonial times from native vegetation to exotic grasses, with potential effects on the spawning dynamics of fish. Here, we used a series of experiments to test preferences of G. maculatus for egg laying in combinations of a native sedge and rush, and two exotic grasses. In laboratory experiments, G. maculatus spawned in all available habitats with no preference for native over exotic vegetation. Egg survival did not differ between the vegetative habitats, but in a treatment where only river stones were available, eggs were laid but they dehydrated and died. In a field experiment, there was no evidence for a preference for spawning in native vegetation, and no association between a “key” feature of vegetation—tiller density—and the number of eggs laid. The microclimate beneath dense vegetation in experimental treatments was more constant than ambient conditions with few extreme temperatures and low humidities. Given the readiness of G. maculatus to spawn in exotic vegetation, there appears to be no benefit in restoring native vegetation to enhance egg laying or survival of these taxa.