Winter-duration treatments used in our experiment were based on historical (1994–2010) field measurements of water temperature from a central Lake Erie water intake located near Cleveland, OH, USA (41° 32′ 53′′ N, 81° 44′ 60′′ W). The short winter duration (52 days) was similar to the number of days below 5 °C recorded during winter 1999 (N=59 days below 5 °C), which was, until 2012, the warmest winter on record for Ohio (1895–2013)56. Our long winter duration (107 days) was equal to the mean number of days below 5 °C observed during 1994–2010. Each winter duration treatment had six replicate tanks, although fertilized samples for embryo hatching success and larval size-at-hatching were only obtained from four replicate tanks in each treatment. All data are presented as tank means±1 s.e. (1–3 observations per tank). Large eggs hatched at higher rates (linear regression: embryo hatching success=0.37·egg mass−0.5) and produced larger larvae (linear regression: larval total length=0.27·egg mass+4.3) than small eggs.