Why Does My Dog’s Breath Smell Like Fish? (5 Gross But Real Reasons)

You are sitting on the couch, enjoying a quiet, relaxing evening after a long day. Your dog jumps up next to you, tail wagging rhythmically against the cushions. They look at you with pure adoration, lean in for a big, sloppy kiss, and… you recoil.

It doesn’t smell like normal “doggy breath.” It doesn’t even smell like the kibble they just ate for dinner. It smells distinctly, overpoweringly… fishy.

It’s a sharp, metallic, pungent odor that hits the back of your throat. It reminds you of a fish market on a hot summer day or a can of tuna that has been left open for too long. The weirdest part? You haven’t fed them fish in weeks.

If you are frantically Googling “Why does my dog’s breath smell like fish?”, first of all: I am sorry. It is a terrible, lingering smell. Second: Do not panic.

As a pet care specialist, I hear this complaint all the time. While it is certainly gross (and embarrassing if you have guests over), it is rarely a life-threatening emergency. However, it is a very specific “red flag” that points to a few distinct medical issues. It is not something you should simply try to mask with a minty dental chew; you need to find the source.

In this comprehensive guide, we will play detective. We will uncover the “Big Two” causes (one involves the mouth, the other involves the… rear end), explore other potential medical reasons, and give you a step-by-step action plan to get your dog’s breath fresh again.

1. Anal Glands: The Butt-to-Mouth Connection

I know, I know. You didn’t want to read this. You wanted the answer to be “he ate a sardine.” But if your dog’s breath smells like fish, this is the culprit about 70% of the time.

To understand why, we need a quick anatomy lesson. Dogs have two small sacs located on either side of their anus (think of them sitting at the 4 o’clock and 8 o’clock positions). These sacs are technically scent glands. In the wild, they act like your dog’s personal ID card. When a dog poops, these glands naturally express a tiny amount of fluid that puts their unique signature on the stool.

The fluid inside these glands has a very distinct profile. It is thick, oily, brownish-gray, and smells extremely pungent, metallic, and—you guessed it—fishy.

How Does the Smell Get to the Mouth?

Dogs are incredibly clean animals. If their anal glands are full, impacted (blocked), or leaking, they feel a sense of pressure or itching. It’s uncomfortable, like having a pebble in your shoe that you can’t remove.

To relieve this pressure or itch, they do two things:

• Scooting: Dragging their bottom across your favorite rug.
• Licking: Excessive grooming of the tail base and rear end.

Here is the unfortunate reality: When they lick to clean themselves or relieve pain, that potent, fishy fluid gets on their tongue and around their muzzle. Five minutes later, they come to lick your face to say hello, and you are hit with that terrible odor.

Signs It Is the Anal Glands:

Aside from the breath, look for these clues:

• The “Scoot”: Moving their butt along the floor.
• Chasing the Tail: Trying to reach their rear end frantically.
• Discomfort: Trouble sitting down or jumping up quickly.
• Redness: Swelling around the anus.

The Solution: You need a “butt check.” Take them to the vet or a professional groomer to have their glands “expressed” (manually emptied). Once the glands are empty and the pressure is gone, the licking will stop, and the breath will return to normal.

2. Periodontal Disease: The Silent Infection

If you are 100% sure your dog hasn’t been licking their backside (perhaps they are wearing a cone, or you’ve been watching them all day), the next most common reason why a dog’s breath smells like fish is severe dental disease.

This isn’t just a little bit of plaque. We are talking about advanced Periodontal Disease.

Why Does Dental Disease Smell Like Fish?

When plaque hardens into tartar (calculus), it pushes the gums away from the teeth, creating deep “pockets.” Food particles and bacteria get trapped in these pockets where your toothbrush can’t reach. Over time, this bacteria breeds, multiplies, and causes tissue decay.

Certain types of anaerobic bacteria that thrive in infected gum tissue produce volatile sulfur compounds. To the human nose, these compounds don’t smell like “rotten food”—they smell distinctly metallic, rusty, or fishy. It is essentially the smell of active infection and decaying gum tissue.

How to Check Your Dog’s Mouth

Lift your dog’s lip gently and look for:

• Red, inflamed gums (Gingivitis) instead of healthy pink ones.
• Brown or Yellow tartar buildup, especially near the gum line.
• Bleeding spots on their chew toys or bedding.
• Loose teeth or reluctance to eat hard kibble.

The Solution: A professional dental cleaning. No amount of brushing at home will remove tartar that has hardened below the gum line. Your vet will need to put them under anesthesia to scrape the teeth clean and polish them. This usually fixes the breath instantly.

3. Kidney or Liver Disease (The Serious Stuff)

While less common than butt-licking or bad teeth, a persistent bad odor can sometimes be a subtle sign of internal organ issues. It is important to rule these out, especially if you have a senior dog (over 7 years old).

Kidney Failure

The kidneys are the body’s filtration system. When they start to fail, they stop filtering toxins (like urea and nitrogen) out of the blood effectively. These toxins build up in the system and eventually make their way to the saliva.

• The Smell: Often described as “urine-like,” ammonia, or a metallic/fishy odor.
• Other Symptoms: Drinking excessive amounts of water, urinating frequently, vomiting, weight loss, and general lethargy.

Liver Disease

The liver also filters toxins. If it is struggling, it can produce a very foul, musty odor in the breath known as Fetor Hepaticus.

• The Smell: Musty, dead, or fishy.
• Other Symptoms: Yellow gums or eyes (jaundice), vomiting, lack of appetite, and a distended belly.

Warning: If your dog’s breath smells like fish AND they are acting sick (vomiting, not eating), this is a medical emergency. Do not wait.

4. Diet and Supplements: The Obvious Choice

Sometimes, the answer is sitting right in your pantry. Have you recently changed their food or added a new topper?

If you are feeding a Fish-Based Food (like Salmon, Whitefish, or Trout formulas), the oil can linger in the mouth long after eating. Fish oils are sticky and potent.

Supplements to Check:

• Omega-3 Softgels: Are you popping a fish oil pill into their bowl for their coat?
• Salmon Oil Pumps: Great for the skin, terrible for the breath.
• Treats: Many high-value training treats are made from dried fish skins, sprats, or green-lipped mussels.

The Fix: If this is the cause, it’s harmless! You can switch to a chicken or beef-based food, or simply brush their teeth after meals if the smell bothers you. You can also look for “odorless” Omega supplements.

5. Oral Tumors or Mouth Ulcers

This is rare but possible. Growths in the mouth (oral tumors like Melanoma or Squamous Cell Carcinoma) can grow rapidly. As they get bigger, the blood supply to parts of the tumor might get cut off, causing that tissue to die (necrose).

Dead tissue attracts bacteria and causes a horrible, rotting-fish smell. It is different from the smell of plaque; it is often more “meaty” and offensive.

Do a quick check: Lift your dog’s lip. Do you see any lumps, bumps, or strange cauliflower-like growths on the gums or roof of the mouth? If so, book a vet appointment today.

Home Remedies: How to Freshen the Breath

While you wait for your vet appointment, or if you’ve confirmed it’s just a minor issue, here are some ways to combat the stink when your dog’s breath smells like fish.

1. Daily Brushing (The Gold Standard)

Nothing beats mechanical scrubbing. Use a dog-specific enzyme toothpaste (never human toothpaste, as fluoride is toxic). Brushing once a day prevents the bacteria that cause the fishy smell from colonizing.

2. Water Additives

There are odorless, tasteless liquids you can add to their water bowl (like “Dental Fresh”). They contain enzymes that help break down plaque and kill odor-causing bacteria in the saliva every time they drink.

3. Crunchy Veggies

Carrots and apple slices (without seeds) act as natural abrasive chews. They help scrape mild plaque off the teeth and increase saliva production, which washes away smells naturally.

4. Parsley & Mint

Sprinkle a little fresh chopped parsley or mint over their food. Parsley contains chlorophyll, which is a natural deodorizer. (Ensure it is just plain garden mint, not essential oils).

5. Wash the Bedding

This is a step many owners forget. If the cause was anal glands, that fishy fluid is likely on their blankets, bed, and your couch where they were scooting. Wash everything in hot water to stop them from re-scenting themselves.

When to See a Vet?

Not every bad breath day requires a doctor, but fishy breath is specific. You should book an appointment if:

• The smell persists for more than 24 hours despite brushing.
• You see “Scooting”: They need their glands expressed professionally.
• Eating Habits Change: If they are dropping food or chewing on one side, it indicates dental pain.
• Systemic Signs: Vomiting, diarrhea, or drinking too much water.

Frequently Asked Questions (FAQ)

Q: Can I express my dog’s anal glands at home?
A: Technically, yes, there are YouTube tutorials. However, I do not recommend it. It is very easy to do incorrectly. If you squeeze too hard or at the wrong angle, you can rupture the gland inside the body, causing a painful abscess and a massive vet bill. It is smelly, messy work best left to groomers or vets.

Q: Why does my dog’s breath smell like fish after sleeping?
A: This is likely “Morning Breath” combined with the fact that dogs often groom themselves (and their rear ends) right before bed or during the night. The smell lingers in the dry mouth while they sleep.

Q: Are there dog breeds more prone to fishy breath?
A: Yes. Small breeds (Chihuahuas, Yorkies, Pugs) are more prone to both Anal Gland issues (they don’t empty well naturally) and Dental Disease (crowded teeth). So, they are the “frequent flyers” for fishy breath.

Q: Will dental chews fix the fishy smell?
A: They might mask it for 20 minutes, but they won’t cure it. If the cause is impacted anal glands or a rotten tooth, a Greenie won’t help. You need to treat the root cause.

Final Thoughts

Dealing with a pet whose dog’s breath smells like fish is unpleasant, but it is your dog’s way of telling you something is wrong. Whether they need a “butt squeeze” (anal gland expression) or a dental cleaning, addressing the issue will make both of you happier.

Don’t ignore the stink. Check the rear, check the teeth, and call the vet. Soon enough, those puppy kisses will be sweet again (or at least, bearable!).

For more expert tips on keeping your pup fresh, healthy, and happy, be sure to browse our full Dog Health and Care section.