The fishy breath in dogs can be due to the various reasons. One of the most common is the dental decay especially in the older dogs. If you take a look at the teeth of your dog, you can notice that he may have red gums which are accompanied by the dark color teeth due to the accumulation of tartar. A veterinary doctor can exam the teeth of your dog and schedule a dental cleaning if this is the issue.

The fishy smell may also derive if dogs have recently licked his anal glands that are in need to be expressed. Anal glands of dogs have a characteristic fishy smell. If you smell this fishy smell towards the rectum of dog, it is very likely that your dog has licked his anal glands.

A temporary stomach upset may also cause a bad breath odor in your dog. You can try to feed your dog a bland diet of boiled rice and hamburger for a couple of days and see if his breath gets better. The fishy breath in the dogs is not always a bad sign and in some instances this odor simply derives from some food he recently ate.

Sometimes there are systemic diseases, such as diabetes or kidney problems, which can cause the bad fishy breath. A veterinary doctor will be needed in these cases for the proper testing of fishy breath in dog.