Reproduction of littoral-spawning lacustrine fishes can be constrained by unfavourable water levels conditions in impoundments during breeding seasons. This is especially the case when spawning sites are restricted to certain types of substrata in systems with dynamic hydrological regimes and heterogeneous habitats. Arthurs Lake and Great Lake, central Tasmania, Australia are integral resources within the Tasmanian hydro-electric power scheme. Collectively, endemic and threatened Paragalaxias dissimilis, P. eleotroides and P. mesotes occur in these lakes and water level fluctuations have the potential to impact their populations. Interactions between: (1) the reproductive strategies of these fishes, (2) lake habitats, and (3) water level regimes were examined over a 5-year period encompassing variable hydrological conditions.

Paragalaxias species in Arthurs Lake and Great Lake have strong habitat-specific requirements for spawning, with discrete egg clusters being adhered to the undersides of boulders at a median depth of 0.68 m (0.1 and 0.9 quantiles of 0.38 and 1.18 m, respectively) during spring-summer. Habitat mapping found limited areas of substrata in these lakes that could be suitable for spawning, and relationships between water levels and inundated spawning substrata were non-linear, with critical thresholds evident at relatively low water levels. In addition, biological traits such as low fecundity (<400 eggs per fish) and short longevity (predominance of fish <3 years of age) may limit the resilience and resistance of these fishes to water level-induced recruitment failures. To sustainably manage water levels in systems containing paragalaxiids, prescriptions that protect paragalaxiid breeding should be included in operational regimes.