Thermal dependence of size-at-hatch in the lake whitefish (Coregonus clupeaformis)

Lake whitefish (Coregonus clupeaformis) embryos incubated at low temperatures have a longer incubation period andhatch at a significantly greater size than those incubated at warmer temperatures. We examined hatch timing and morpholog-ical characteristics for whitefish embryos reared under different constant and varying temperatures to determine whether thethermal dependence of hatching size reflects differences in their development stage. Our results show that lake whitefishembryos hatch at different temperature-dependent developmental stages, and this is the dominant factor affecting size-at-hatch.The term “heterograde” is proposed for the thermal dependence of hatching stage to differentiate it from hatching that occursat a fixed developmental stage. A method to quantify this effect is given using a ratio that describes the difference in relativedevelopment at hatching between different viable constant incubation temperatures. Heterograde hatching is proposed as apossible mechanism to synchronize the timing of hatch to the break-up of winter ice cover despite variability in the date ofspawning and in the onset of spring break-up.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author