The offspring of wild-caught specimens, having become docile after having been bred for many generations, fall under the fancy type.

Domesticated rats are physiologically and psychologically different from their wild relatives, and typically pose no more of a health risk than other common pets.

It is believed that both rat-catchers and sportsmen began to keep certain, odd-colored rats during the height of the sport, eventually breeding them and then selling them as pets.

[1][6] The two men thought to have formed the basis of rat fancy are Jack Black, self-proclaimed rat-catcher to Queen Victoria, and Jimmy Shaw, manager of one of the largest sporting public houses in London.

[1][7] Black, specifically, was known for taming the "prettier" rats of unusual color, decorating them with ribbons, and selling them as pets.Rat fancy as a formal, organized hobby began when a woman named Mary Douglas asked for permission to bring her pet rats to an exhibition of the National Mouse Club at the Aylesbury Town Show in England on October 24, 1901.

[citation needed] While domesticated rats are not removed enough from their wild counterparts to justify a distinct species (like the dog versus grey wolf), there are significant differences that set them apart; the most apparent is coloring.

Most wild R. norvegicus are a dark brown color, while fancy rats may be anything from white to cinnamon to blue.

[19] Ruby refers to eyes which at a glance appear black, but on closer observation are a deep, dark red.

Color names can vary for more vaguely defined varieties, like lilac and fawn,[18] while the interpretations of standards can fluctuate between (and even within) different countries or clubs.

However, many domestic rats are not closely bred to any color standard; many of those found in pet shops will have mismarkings from a formal breeding perspective, which are defined as variations in markings that are not recognized as conforming to a breed standard published by a rat fancier organisation.

This strain of dwarfism is caused by reduced production of growth hormone, and this has other effects in addition to changed overall body size.

Unlike a double rex, this type of hairless rat is incapable of growing hairs on any part of the body.

One additional subset of semi-hairless rats, patchwork rex, constantly lose their hair and regrow it in different "patches" several times throughout their life.

[30][31] On one hand, breeding rats to "conform" to a specific standard or to develop a new one is a large part of what the fancy was founded on.

In other areas, like the Canadian province of Alberta, which is considered rat-free,[35] the ownership of domestic fancy rats outside of schools, laboratories, and zoos is illegal.

They may also more easily avoid vectors like cockroaches, beetles, and fleas which are essential for the spread of endemic typhus and intestinal parasites like the rat tapeworm.

[37][38] Additionally, pet or laboratory rats enjoy the intrinsic benefits of having a consistent and well-balanced diet, along with access to medical care.

It may appear like dried blood, but is a mucus-like substance that is released at times of stress or if the rat has a respiratory infection.

Mites are microscopic bloodsucking parasites that can irritate the skin of fancy rats, and if they have a preexisting health condition, it can cause them to die from their bodies' inability to handle two problems at once.

[37][41][42] Specifically, Tyzzer's disease, protozoic infections (e.g. Giardia muris), and pseudotuberculosis are usually seen in stressed or young rats.

[43] Several diseases, like Rat Coronavirus Infection (RCI), Sendai virus, and Murine Respiratory Mycoplasmosis (MRM, Mycoplasma pulmonis), are prevalent simply because their highly contagious natures work in tandem with the way rats are kept in laboratories, pet stores, and by breeders.

[43] Pet rats can also develop pituitary tumors if fed high-calorie diets,[36] and ringtail if placed in areas with low humidity or high temperatures.

are a mostly benign group of bacteria that commonly reside on the top of the skin, but cuts and scratches from social and hierarchical fighting can open up the pathways for them to cause ulcerative dermatitis.

Dietary changes are among the main suggestions for improved health and longevity in fancy rats, including feeding rat-friendly superfoods [46] in moderation to reduce the risk of cancers, heart disease, and stroke.

This disease is fairly unnoticeable in the rat, but is characterized by swelling of the bite or scratch site, fever, vomiting, and body aches.

While these movies generally emphasize the popular perception of malevolence[53]—they kill people and cats and ransack grocery stores—other wild rats who become pets are portrayed in more neutral to positive ways; the television show, House, briefly featured "Steve McQueen", the pet rat of the titular character.

Ronald Weasley has a pet rat, Scabbers, who was later revealed to be an illegal animagus named Peter Pettigrew in reality.

Christopher Boone, the autistic protagonist of The Curious Incident of the Dog in the Night-Time has a pet rat named Toby.

[55] Roddy St. James (voiced by Hugh Jackman), the main character in the DreamWorks animated film Flushed Away, is a fancy rat kept as a pet by a family in Kensington, London.