Backed up anal glands are one of the main reasons why a dog may smell like fish. A dog's anal glands normally drain when the dog has a bowel movement. However, when the sacs do not drain normally, they become backed up and can be uncomfortable or painful to dogs.
The easiest way to alleviate backed up anal glands is by expressing the glands. Generally, it is best to have a veterinarian express the glands to rule out other issues such as infection. One of the best ways to help prevent anal gland blockage in dogs is by feeding them a diet that is rich in fiber.