Why does my dog's breath smell like dead fish?

If your dog's breath smells bad, that could indicate a number of things. Most of the time, it may mean that his teeth need to get cleaned. Dogs need regular dental cleanings just like people, just not as frequently. Your vet should examine your dog's teeth and mouth during their yearly physical exam. If you notice a lot of plaque and tartar building up your dog's teeth (usually brown or black coloration or crusting towards the bottom of the teeth), then it may be time for a cleaning, which is performed under anesthesia. Sometimes, teeth may need to be removed if enough disease is present to cause cavities or rotting. Other things that could cause bad breath include masses or ulcers inside the mouth or having unregulated diabetes. In any case, a quick exam with your vet could determine the cause and appropriate course of treatment.

Dental care for your pet is just as important as our oral health is to us. And, it doesn't matter how many dental treats or chews you give. If you don't brush their teeth you'll never remove all the bacteria etc. unfortunately, by the time you notice a smell it could be an indication of an infected tooth. Your vet most likely offers dental cleanings, so I would definitely check with them.