Why does my dog smell like fish?

A question that is often asked by new and inexperienced dog owners is “Why does my dog smell like fish?” It might seem strange that your dog’s breath suddenly starts smelling of fish and that they start to leave a fishy smell behind them, for example on the couch. However, there’s actually an important medical explanation for it.

Why Does My Dog Smell Like Fish?

Why does my dog smell like fish?

At the same time as noticing the fishy smell, the dog owner will likely also have noticed that their dog has developed the rather unpleasant habit of constantly licking, or scratching and biting, their butt. The dog may also have started to drag their butt all across the floor. This is known as scooting. They may also have started to chase their tail.

All of these things are signs that your dog’s anal sacs need to be emptied because they’re not emptying on their own.

The anal sacs

The anal sacs contain a brown, smelly fluid. When all is going to plan, the anal sacs (also often referred to as the anal glands) will empty themselves of this fluid naturally when your dog goes to the toilet.

But sometimes the sacs don’t empty or only partially empty. The end result of this can be that the sacs become full. This can cause discomfort for your dog, the evidence of which is what you’re seeing when your dog starts to scoot along the floor or licking their butt. This build up of fluid can also cause infection and abscesses if not treated.

Although it’s a quite straightforward and simple process to manually empty the anal sacs yourself once you know how to, I recommend that you take your dog to the vets to get it done the first time. The reason for this is so that the vet can check for infection or any other problems. Alternatively, your dog groomer should also be able to empty the anal glands for you.

What causes the anal sacs to fill?

Some small dogs such as the Lhasa Apso and the Chihuahua are thought to be more likely to suffer from this problem than other dog breeds, although a lot of the evidence for this is anecdotal rather than as the result of scientific studies.

Whatever the breed of dog though, the usual cause of your dog’s anal sacs not emptying properly and becoming full is your dog’s diet.

If your dog is producing hard, firm stools then the anal sacs will normally empty just like they’re supposed to.

If your dog’s stools are soft and runny on the other hand, then the anal sacs may not empty, or may not empty enough, and will eventually fill up.

To avoid this, you should make sure that you feed your dog a fiber-rich diet and not give them food with a lot of filler in it. Then your dog’s stools are more likely to be firmer and the anal sacs are more likely to empty properly, without intervention.

Other possible causes of the anal sacs not emptying properly include your dog being overweight, changes in the nature of the fluid (it becomes thicker for some reason), and muscle weakness. Sometimes a dog will just produce too much of the fluid found in the anal sacs too.

If your dog is obese and you suspect this is the reason for their anal sac problems, put them on a diet to lose weight and make sure they get plenty of exercise. Getting plenty of exercise can also help if lack of muscle tone is the cause of the problem.


Many dog owners suddenly find themselves asking why their dog smells like fish. If you notice that your dog has suddenly started to smell of fish and is also licking or biting their butt and scooting, then the dog’s anal sacs likely need to be emptied.

The vet or your dog groomer can do this, or you can even do it yourself. What is important is that it is done, to prevent infection and other problems, such as impaction of the anal sacs, from developing.

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