If you want fit, strong, healthy gerbils you need to give them a run every day and make sure you handle them. When you first get your gerbils they might bite but don't worry it  doesn't hurt. Make sure you give them paper and cardboard like  tissue boxes and toilet rolls. Some people say to pick them up by their tails but don't they hate it and it hurts them. Don't put them near loud music or TV because it can deafen them. Gerbils can climb well so get a tall run so they can't escape. If you do lose a gerbil put out some food and wait for it to turn up and be very quiet. Gerbils will eat their tissue box after a while so give them old jars (clean them out first). Give gerbils a glass water bottle or they will eat it and make their home wet. Try not to disturb gerbils when they sleep or they will bite you.