Temperature-dependent larval survival and growth differences among populations of Murray cod (Maccullochella peelii)

Different populations of organisms can vary widely in their responses to environmental conditions and this variation is fundamental to the persistence of species. Using a common garden experiment, we examined temperature-specific growth and survival responses of larvae among populations of Murray cod (Maccullochella peelii) from four regions of the Murray-Darling Basin (MDB), Australia. Fish larvae from the four regions differed significantly in their growth and survival responses at high water temperatures 26 degrees C. At 30 degrees C, survival rates of larvae by Day 20 ranged from 0% in the Lachlan region to 82% in the southern region. Opposite to the geographical differences in survival, growth of larvae was highest in the Lachlan (14.8-15.4-mm standard length 95% CI) and lowest in the southern region (13.4-13.9-mm standard length 95% CI) at 26 degrees C where sufficient numbers survived for comparison. Geographical differences in growth and survival responses did not follow a consistent latitudinal gradient as observed for other species, but were closely linked with previously described genetic structure. Our results suggest that the upper thermal limit of M. peelii larvae is near common river temperatures in the MDB and that maintaining functional response diversity and underlying genetic diversity will be important for ensuring the resilience of this apex predator under future climate change.