They were so rare they were quite expensive. Because it was soon found that just like any other rodent they breed prolifically, the cost became much lower. They are about the size of a hamster but the fur is grayish brown and they have a slight coat of oil on the fur, which accounts for their fluffiness. They are not as easily startled as mice are but nearly as hyperactive. They also don't seem as quick to bite.
Gerbils are the easiest of the rodents as far as maintenance.
They are actually a desert animal whose body has developed the ability to utilize almost all the water they take in. The tank is a good idea for gerbils because they love to dig and make holes and this tends to throw their bedding all over and out of a wire cage. The tank keeps the bedding inside and less messy. You can purchase commercial gerbil food at your local pet shop. Give them snacks such as raw oatmeal, peanut butter, dry breakfast cereal, and popcorn.