Instructions
Decide whether you prefer a male or female. While lazier and usually more docile, males can have a bit more odor because they may engage in urine-marking behavior and might even piddle in your lap. On the other hand, they're also more likely to cuddle up for an ear scratch. Very occasionally they'll fight with other males, particularly if they're not purchased simultaneously. Females are more active and adventurous and seemingly very busy all the time. They're slightly smaller, have softer fur, are less likely to mark territory and can be kept with other females.
Slowly and carefully put your hand into the cage of prospective candidates. Avoid any individuals that don't immediately approach to investigate, whether they're males or females. Well-socialized pet rats are naturally curious and outgoing animals that won't be afraid or even a little wary of humans.
Pick up a very young rat and gently turn it over onto its back. By the time it's 12 to 21 days old, the female will have two visible rows of six teats. The male will have none. If you compare a male with a female, you'll also see a noticeable difference in the distance between the urethral and anal openings. The female's two structures are close together, while the males are farther apart. Both will have identical black bellybuttons.
Observe adult rats from side and rear angles, as the testicles will be obvious in individuals 6 weeks of age and up. If not, lift a tail. Typically, if you don't see anything, the rat's a girl.
How to Tell a Male from a Female Rat
Although young rats purchased from pet shops can make good pets, there's no way to predict genetic temperament, health or longevity. As with any other pet, those purchased from reputable breeders are superior companions. Male and female rats well-socialized as babies are clean, gentle pets. In fact, other than guinea pigs, rats are the least likely rodents to bite you. Opt for a rat at least 6 weeks of age, when testicles of males become noticeable. If in doubt, compare candidates of similar ages by picking them up one by one and examining their genitalia until you identify two that look very different from each other.