Good job on the spawn! To answer the question about the garage getting too cold: it's heated to 45 all winter long. Regardless, I keep the more northern species out there- these fish endure lakes that freeze over in the winter. The ice up here gets deep enough to drive cars on, so that gives you an idea of how cold the water can get. I know of many people that barely keep the water from freezing. They might feed the fish once all winter, and they live through it.