Minecraft wiki entry for Bucket_of_aquatic_mob, associated text: If a bucket of aquatic mob is named a certain name through an anvil, the mob inside display that name as if it were named with a name tag, making fishes and axolotls the only mobs that can exist in item form, and be named without a name tag.‌[Java Edition only] Alternatively, if a named mob is captured with a bucket of water, the resulting mob bucket shares a name with the captured mob.‌[Java Edition only] If a named mob is captured in Bedrock Edition, the item is called "Bucket of <Name>".