If you’re too cold to eat, you’re in trouble. It’s a very different story if you’re a fish, though. I have found that when the temperature of the water in the fish barrel is below 42°F (6°C), the fish simply aren’t interested. After a little research, I found that goldfish can go for weeks, even months, without eating at all. Not only that, they can be frozen solid, then thawed out after several years. But that tends to kill them.