Is it permissible to move an animal on Shabbat? For example, if a person wants on Shabbat to play with a pet parrot, or move an aquarium containing fish, is this allowed, or do we consider pets Mukse?
The Shulhan Aruch (Orah Haim 308:39) explicitly writes that all animals are considered Mukse on Shabbat, emphasizing that this applies to domesticated and non-domesticated animals, and to birds. One might have argued that an exception could be made for pets, with which one plays and uses for enjoyment. In fact, Tosafot (Talmud commentaries by Medieval French and German scholars), in Masechet Shabbat (45b), cite the ruling of Rabbi Yosef (one of the Tosafists) that live chickens are not considered Mukse on Shabbat, because children would play with them and parents commonly used chickens as toys to pacify crying children. Seemingly, then, we might say that all pets with which people enjoy playing should not be considered Mukse, since they serve as toys and sources of enjoyment.
In truth, however, this is not the case. For one thing, this view of Rabbi Yosef, although it is also shared by a Rabbi called Rabbenu Shimshon, represents the minority view among the Rishonim (Medieval Halachic scholars). The vast majority of scholars held that no distinction is made between different kinds of animals, and they are all considered Mukse on Shabbat. Furthermore, it is uncertain whether even Rabbi Yosef would apply his ruling to pets. He referred to chickens, which were actually used as toys by children, who would hold and play with the chicken. But when a person lifts a parrot, for example, he does not derive direct benefit from the parrot, by using it as a toy, but rater enjoys seeing it or listening to it. Thus, we cannot necessarily extend Rabbi Yosef’s ruling to all pets.
Indeed, Hacham Ovadia Yosef rules that one may not lift or move any animals on Shabbat, including pets. This was also the ruling of Rav Moshe Feinstein (Russia-New York, 1895-1986), who added that one may likewise not move an aquarium containing fish. Since fish are considered Mukse, the aquarium has the status of a "Bassis" ("base") to a Mukse item, and is therefore itself considered Mukse.
Summary: It is forbidden to pick up or move any animal on Shabbat, including pets, and including fishbowls and aquariums containing fish.
