The dwarf galaxias, Galaxiella pusilla, is a small freshwater fish of national conservation significance from south-eastern Australia. Anecdotally it has been suggested by a number of authors that dwarf galaxias are able to survive extended periods of habitat drying (e.g. aestivation, refuge in cray burrows), but it has not been rigorously tested. A series of experiments were conducted to understand the capacity for dwarf galaxias to persist without surface water, including the influence of particular habitat types (sediment only, vegetation, detritus, artificial crayfish burrows) on survival rates, as well as measurements of respiration rates in both water and air. In parallel, we tested the responses of the invasive eastern mosquitofish (Gambusia holbrooki), a major competitor and predator that often threaten dwarf galaxias populations.

Dwarf galaxias survived significantly longer than eastern mosquitofish without surface water, with survival rates strongly influenced by the moisture retention capacity of specific habitats. There were also distinct changes in the physiological response of dwarf galaxias to habitat drying, with transition to a mode of air-breathing clearly evident as water levels receded. On the other hand, eastern mosquitofish appeared to change their breathing rate but not their breathing technique. The enhanced ability of dwarf galaxias to cope with habitat drying was also demonstrated by differences in respiration rates – where oxygen consumption was similar between dwarf galaxias and eastern mosquitofish in water, but significantly lower for eastern mosquitofish in air. This research will help inform dwarf galaxias conservation efforts in regards to the potential risk of local extinction due to extended dry conditions or predicted changes in future climate, and the management of invasive species such as eastern mosqutiofish.