The effects of fluctuating temperature regimes on the embryonic development of lake whitefish (&ITCoregonus clupeaformis&IT)

Fluctuating incubation temperatures may have significant effects on fish embryogenesis; yet most laboratory-based studies use constant temperatures. For species that experience large, natural seasonal temperature changes during embryogenesis, such as lake whitefish (Coregonus clupeaformis), seasonal temperature regimes are likely optimal for development. Anthropogenic activities can increase average and/or variability of natural incubation temperatures over large (e.g. through climate change) or smaller (e.g. thermal effluent discharge) geographic scales. To investigate this, we incubated lake whitefish embryos under constant (2, 5, or 8 degrees C) and fluctuating temperature regimes. Fluctuating temperature regimes had a base temperature of 2 degrees C with: 1) seasonal temperature changes that modeled natural declines/inclines; 2) tri-weekly +3 degrees C, 1 h temperature spikes; or 3) both seasonal temperature changes and temperature spikes. We compared mortality to hatch, morphometries, and heart rate at three developmental stages. Mortality rate was similar for embryos incubated at constant 2 degrees C, constant 5 degrees C, or with seasonal temperatures, but was significantly greater at constant 8 degrees C. Embryos incubated constantly at > 2 degrees C had reduced body growth and yolk consumption compared to embryos incubated with seasonal temperature changes. When measured at the common base temperature of 2 degrees C, embryos incubated at constant 2 degrees C had lower heart rates than embryos incubated with both seasonal temperature changes and temperature spikes. Our study suggests that incubating lake whitefish embryos with constant temperatures may significantly alter development, growth, and heart rate compared to incubating with seasonal temperature changes, emphasizing the need to include seasonal temperature changes in laboratory-based studies.