Why does my dog smell of fish?

Whether it’s your dog’s bottom (anal sacs), their breath, a female in season or a dog that’s been scared or stressed, you may be wondering why your dog sometimes smells of fish. If they do have a strong odour, then it could be a sign your dog has health issues, but when should you be concerned, what should you do and how can you prevent it from happening again?

Why does my dog smell of fish?

If your dog smells of fish, the most common cause is usually problems with their anal sacs, but it could also be a sign of dental issues, digestive conditions or infections. Dogs have small sacs that sit either side of their anus and produce a distinctive smelling liquid that helps other dogs to recognise them. These sacs can become blocked, swollen or infected and can be very painful. Signs of anal sac disorders include your dog licking or biting their bottom, scooting on the ground or finding it difficult to go to the toilet. If you’re concerned about your dog’s health then always speak to your vet for advice.

What are a dog’s anal sacs?

On either side of your dog’s bottom are two anal sacs that produce a strong smelling liquid with a scent specific to them. These secretions help them tell other dogs who they are and mark where they’ve been. This oily, smelly liquid is released each time they have a poo, helping them mark where they’ve been, but it’s also released when they walk around and when they’re stressed or scared. To us, these secretions smell unpleasant, but dogs find them fascinating and they're packed full of information about the dog that produced them, such as who they are, what they’ve been doing and what they’ve been eating. These scent markers are the reason why dogs take such an interest in each other’s bottoms and any poo they find on walks.

What issues can dogs have with their anal sacs?

It’s common for dogs to have problems with their anal sacs. They’re the third most commonly diagnosed health issues, affecting around 4% of dogs seen by vets each year. If these sacs become blocked, swollen or infected they can be incredibly painful and cause the distinctive strong fishy smell you may be familiar with.

Issues with the anal sacs include:
  • Anal sac impaction - These account for nearly 80% of anal sac disorders and are caused by the anal sacs not completely emptying each time your dog has a poo. The remaining liquid can dry up and cause a blockage that prevents the sacs from emptying. Impacted anal sacs can be incredibly painful and if left untreated can lead to infection and abscesses
  • Anal sac infections and abscesses - These account for around 9% of cases, causing the anal sacs to become discoloured or swollen and sometimes even rupture, leading to extreme pain and further complications
  • Tumours - Dogs can be affected by tumours of the anal sacs or of the glands that line their walls. Tumours of the anal glands are usually benign (they don’t spread), are a relatively common tumour and usually affect entire males. Tumours of the anal sacs are different; they tend to be rarer and may spread to other parts of the body. Any abnormal swelling around your dog’s bottom should be examined by your vet.

Signs of anal sac disease

Signs of anal sac issues can include:
  • A strong fishy smell, particularly around your dog’s bottom
  • Scooting on the floor
  • Biting or licking at their bottom
  • Problems going to the toilet
  • Signs of pain when they sit
  • Yelping in pain
  • Hard or discoloured lumps around their anus
  • Blood or pus in their stool
  • An open wound or abscess on their bottom may suggest a ruptured anal sac

If you think your dog may have problems with their anal sacs, it’s important that you speak to your vet before the condition becomes more painful and severe.

Which dogs are prone to anal sac disorders?

In 2021, the VetCompass programme at the Royal Veterinary College, partially funded by The Kennel Club Charitable Trust, conducted research that looked at the veterinary records of over 104,000 dogs. Data from these dogs were analysed to look at which breeds had an increased or reduced risk of anal sac disorders.
The study found that:
  • Breeds with an increased risk of anal sac disorders compared with crossbred dogs included:
    • Cavalier King Charles Spaniels
    • King Charles Spaniels
    • Shih Tzus
    • Bichon Frise
    • Cocker Spaniels
  • Breed types with an increased risk of anal sac disorders included:
    • Flat-faced (brachycephalic) dogs
    • Spaniel types
    • Dachshund types
    • Poodle types
  • Breeds with a reduced risk of anal sac disorders compared with crossbred dogs included:
    • Boxers
    • German Shepherd Dogs
    • Staffordshire Bull Terriers
    • Border Collies
    • Labrador Retrievers

What should I do if my dog smells of fish?

If you notice that your dog smells like fish, or are concerned about their health, then always contact your vet for advice. Your vet will be able to assess your dog and the severity of the issue, and recommend a treatment plan.

Although some groomers offer the service of expressing your dog’s anal sacs, it’s always best to speak to your vet in the first instance, as there could be an underlying health issue that needs to be addressed.

How do I squeeze or empty my dog’s anal sacs?

Anal sac issues can often be a painful problem for dogs, but if your dog does not have anal sac problems then they should be left well alone. It’s particularly important that if this is the first time your dog has shown problems that you do not try to express their anal sacs yourself. Manually emptying their anal sacs can cause trauma and can damage the anal sac duct, so should never be done unless under veterinary direction.

Some dogs need to be treated more than once and your vet may decide to express your dog's anal sacs, but this should never be done without your vet’s guidance. Some groomers may also be able to express anal sacs, but if your dog does need additional help, then you should speak to your vet about the best ways to manage their issue first. Expressing your dog’s anal sacs too often, especially when it's not necessary, can cause further harm or future complications.

How can I prevent anal sac disease?

Any dog can be affected by anal sac disorders and it isn't always be clear why it occurs, but you can take the following actions to try to reduce your dog’s risk of anal sac disorders:
  • Feed your dog a good quality diet that contains the right amount of fibre
  • Make sure they’re getting enough regular exercise
  • Give your dog access to water so that they stay well hydrated
  • Keep an eye on your dog’s stools to ensure they’re not too soft
  • Keep your dog at a healthy weight. Some vets have suggested that dogs with obesity are more likely to develop anal sac issues, while others dispute this. Nonetheless, keeping your dog at a healthy weight is one of the best ways to maintain their overall health
  • Know the signs to watch out for that your dog may be beginning to suffer from anal sac issues

Speak to your vet to ask for further advice about diet, exercise and the steps you can take to reduce the risk of anal sac impaction.

Why does my dog smell of fish when they’re scared?

A dog’s anal sacs produce a liquid that acts as a natural scent marker and are usually emptied when a dog has a poo. These sacs produce a liquid that helps dogs to identify themselves to others. When a dog is scared or stressed they sometimes naturally empty their anal sacs, releasing this distinctive fishy smelling substance. If your dog has emptied their anal sacs when scared then there is no need to contact your vet, but if your dog regularly smells of fish, has other signs, or you’re concerned about their health, then always contact your vet for advice.

Why does my dog’s breath smell like fish?

A dog’s breath can rarely be described as fresh or pleasant, but if your dog smells of fish then it could be a sign of dental issues (infection, tooth decay, abscesses or gingivitis), digestive problems, kidney disease or diabetes. If your dog regularly has fishy or foul-smelling breath then it’s important that you speak to your vet for advice. If your dog does have dental issues, then brushing their teeth regularly may not be enough to get rid of bad breath and they may need to be treated by your vet.

Why does my dog’s urine smell like fish?

If your dog’s urine smells of fish, has a very strong or pungent smell, or suddenly smells different, then it could be a sign of urinary problems, such as a urinary tract infection, bladder or kidney stones. It’s important that you contact your vet for advice before your dog becomes more unwell.

Why does my female dog smell like fish?

If your female dog smells of fish, they may have a problem with the natural balance of normal yeast or bacteria in their vagina. It may also be a sign of a urinary tract infection or pyometra (infection of the womb). If your dog smells unpleasant or different, has any unusual discharge, or seems unwell, then contact your vet.

Find out more

Find answers to some of the other most commonly asked questions on our 'why does my dog?' hub, such as:
  • Why does my dog eat grass?
  • Why does my dog eat poop?
  • Why does my dog shake?
  • Why does my dog stare at me?
  • Why does my dog follow me everywhere?
  • Why does my dog lick me so much?
  • Why does my dog lick my feet?
  • Why does my dog sneeze so much?

Think your dog may be affected?

If you're worried about your dog's health, always contact your vet immediately!

We are not a veterinary organisation and so we can't give veterinary advice, but if you're worried about any of the issues raised in this article, please contact your local vet practice for further information

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