We have a 6 yr old Basenji mix who has been spayed. At least once a monht, she emits a fishy odor that drives our intact Weimaraner insane. Once he gets a whiff, the muscles in his head contract and his jaw quivers. It's not a pleasant smell, but it only lasts for a brief period of time, only to return the next month. Since she was spayed about 5 years ago, I don't know what would cause a cyclical odor.