Gerbils, when you get good ones, usually produce a litter about every five weeks. You leave them in pairs year round. When one dies you just feed the other off. They won't usually accept another mate so late in life.

I usually liked to introduce mine at about eight weeks old when I was breeding a lot of them. They usually don't do well introduced as adults.

I kept mine in 10 gallon tanks, with water bottles, fed them the standard gerbil mix (Kaytee) and kept them on pine shaving. They produced fine, but they are not nearly as prolific as rats or mice.