Why Does My Dog Smell Like Fish? Causes and Care

Vet reviewed. Written by Corinne Homer, Copywriter. Reviewed by Dr. Linda Simon MVB MRCVS, Team Vet.

A fishy smell from a dog often comes from anal sac fluid, but it can also arise from infected skin or ears, periodontal disease, urinary or vaginal disease, food residue or something the dog rolled in. The location and accompanying signs matter more than the odor label. A bath may remove surface odor, but it cannot empty an impacted sac, treat infection or repair a diseased tooth.

Call a veterinarian promptly for pain, swelling beside the anus, blood or pus, difficulty defecating or urinating, vomiting, fever, loss of appetite, facial swelling or marked lethargy. Do not squeeze anal sacs, insert anything into an ear, use human toothpaste or mask a persistent odor with essential oils.

First locate the fishy smell

Notice whether it is strongest near the rear, mouth, ears, paws, skin, urine or vulva. Record scooting, licking, head shaking, bad breath, discharge, accidents, straining and stool change. A towel or collar can hold odor after the source is gone, so check the dog directly and wash bedding separately.

If the smell appeared after eating fish, inspect the lips, beard, bowl and bedding. Diet odor should fade with normal hygiene. Persistent odor with medical signs requires assessment.

Anal sac fluid and anal sac disease

Dogs have two anal sacs beside the anus that contain strong-smelling secretion. Small amounts usually empty during defecation. A frightened or suddenly excited dog may release fluid even without disease. Repeated odor, scooting or pain can indicate impaction, inflammation, infection, abscess or, less commonly, a tumor.

Symptoms of anal sac problems

• Scooting or sudden attention to the rear
• Licking or biting near the anus or tail base
• Pain when sitting or defecating
• Swelling, redness, discoloration or a draining wound
• Constipation or repeated straining
• Recurring strong fishy odor

How anal sac disease is diagnosed

A veterinarian performs a physical and rectal examination. Infected material may be examined microscopically or cultured. A firm enlarged nonexpressible sac can require imaging and biopsy because infection and neoplasia can feel similar.

Treatment

Treatment depends on whether the sac is impacted, infected, abscessed or abnormal for another reason. It can include gentle professional expression, flushing, local or systemic medication, drainage or surgery. Repeated routine expression is not appropriate for every healthy dog and can irritate tissue.

Prevention and fiber

Veterinarians sometimes recommend supplemental fiber to increase fecal bulk and support natural sac emptying. The right type and amount varies, and fiber does not cure every recurrence. Maintain lean body condition, investigate chronic soft stool and follow the plan in our anal gland nutrition guide.

Yeast or bacterial skin and ear disease

Overgrowth and infection on skin or in ears can produce musty, sour or occasionally fish-like odor. Underlying allergy, moisture, anatomy, parasites and hormonal disease may allow recurrence. Food change without cytology can miss the actual organism and cause.

Symptoms

Look for itching, licking, head shaking, greasy scale, redness, dark discharge, hair loss, thickened skin or pain. Paw and ear disease often occur together in allergic dogs.

Diagnosis and treatment

The veterinarian may use cytology from a skin or ear sample and examine the ear canal. Treatment can include topical or systemic antimicrobial medication and management of the underlying trigger. Never use vinegar, peroxide, essential oil or leftover ear medication in a painful ear because a ruptured eardrum changes what is safe.

Prevention

Dry the ears and coat after swimming, follow any prescribed maintenance routine and maintain parasite control. Recurrence is a reason to revisit diagnosis, not simply clean more often.

Dental disease and fishy breath

Periodontal disease is infection and inflammation of the tissues supporting teeth. Plaque bacteria, inflamed gums, periodontal pockets, loose teeth or an infected root can create strong odor. A piece of food trapped in the beard is different and should resolve after cleaning.

Symptoms

Watch for persistent bad breath, visible plaque or tartar, red or bleeding gums, drooling, dropping food, chewing on one side, facial swelling or reluctance to have the mouth touched. Dogs can continue eating despite substantial pain.

Diagnosis and treatment

A complete periodontal evaluation requires anesthesia, probing and dental radiographs to assess disease below the gumline. An awake scraping may improve appearance but does not diagnose or treat hidden periodontal pockets. Diseased teeth may require extraction or specialist treatment.

Prevention

Daily brushing with dog toothpaste has the strongest home-care role. Introduce handling gradually and use products appropriate for dogs. Our plaque and tartar guide explains what home care can and cannot accomplish.

Urinary tract disease or vaginitis

Urine itself can develop a strong odor, and discharge from the vulva can smell unusual. Urinary infection, stones, incontinence, skin-fold irritation, vaginitis and reproductive disease can overlap. Odor alone cannot tell them apart.

Symptoms

Frequent small urinations, straining, accidents, blood, licking, discharge, increased thirst or discomfort needs assessment. A dog repeatedly trying and unable to pass urine is an emergency.

Diagnosis and treatment

Testing can include urinalysis, urine culture, imaging and examination of the vulva and vagina. Merck recommends urinary testing when vaginitis is investigated because bladder disease can be concurrent. Antibiotics should be selected for a documented infection rather than odor alone.

Prevention

Provide fresh water, regular toilet opportunities and hygiene for skin folds when directed. Recurrent infection requires investigation of underlying risk. Do not add cranberry, acidifiers or supplements without the veterinarian because some stone types need the opposite urine target.

A fish-heavy diet

Fish-based food, fish oil or treats can leave odor on the mouth, beard, bowl and bedding. Check storage because rancid oil smells strong and should not be fed. Follow refrigeration and expiration instructions and clean bowls after each meal.

Diet odor should not cause painful defecation, swelling, discharge or urinary signs. Do not let an obvious fish ingredient explain away a medical problem.

Something the dog rolled in

Dogs can pick up dead-animal, pond, trash or fecal odor on the coat. Wear gloves, prevent licking and rinse promptly with dog-safe shampoo. Contact a veterinarian for toxin exposure, skin irritation, vomiting or ingestion of decomposed material.

Can a bath remove the fishy smell?

A bath can remove material on the coat but will not treat anal sac disease, ear infection, periodontal disease or urinary illness. Use stable footing, comfortably warm water and dog shampoo. Rinse and dry thoroughly.

What not to do

• Do not repeatedly express anal sacs at home without training and direction.
• Do not use essential oils or human fragrance on the dog.
• Do not put peroxide, vinegar or cotton swabs into an ear canal.
• Do not scrape tartar or use human toothpaste.
• Do not give leftover antibiotics.
• Do not treat urinary signs with supplements before testing.

When to worry

Same-day care is appropriate for recurring odor with scooting, pain, discharge, licking, head shaking, bad breath or urinary change. Urgent or emergency care is needed for a ruptured swelling, inability to defecate or urinate, facial swelling, collapse, severe pain, repeated vomiting, marked weakness or fever.

A sudden fishy release in a frightened dog that immediately returns to normal may simply be anal sac secretion. Clean the coat and watch. Repetition still deserves discussion with the veterinarian.

What to record before the veterinary visit

Write down when the odor began, whether it is constant or episodic and the part of the dog where it is strongest. Note scooting, licking, head shaking, scratching, drooling, chewing on one side, appetite change, bowel movements, urination, discharge and recent swimming or grooming. A short video of scooting or discomfort can help when the behavior does not occur in the exam room.

Bring the names of the complete food, treats, dental products, supplements and medications used during the previous several weeks. Also report any recent diet change, diarrhea, constipation, antibiotics or repeated anal sac expression. This history helps separate a one-time release of normal anal sac fluid from recurring disease and helps the veterinarian decide whether the mouth, ears, skin, rectal area or urinary tract needs closer testing.

Do not clean an inflamed ear canal, squeeze a swelling or apply fragranced products immediately before the appointment unless the clinic instructs you to do so. Cleaning may remove discharge that would otherwise support cytology or culture, while squeezing can increase pain or rupture fragile tissue. If the dog is trying to bite the area, use safe supervision and ask the clinic about preventing self-trauma.

Odor intensity does not reliably measure severity. A small amount of normal anal sac fluid can smell dramatic, while advanced dental or skin disease may develop gradually enough that a household stops noticing it. Recurrence, pain, swelling, discharge and changes in eating or elimination are more useful urgency signals than whether another person can smell the dog across the room.

Frequently asked questions

Why does my dog's rear smell like fish?

Anal sac fluid is common, but recurring odor with scooting, pain or swelling can indicate impaction, infection or another anal sac problem.

Why does my dog's breath smell fishy?

Fish-based food can leave residue, but persistent odor can indicate periodontal disease or another oral problem and warrants an examination.

Can I express my dog's anal glands at home?

Not routinely without veterinary training and a reason. Incorrect or repeated expression can cause pain and tissue irritation and may miss an abscess or mass.

Will changing food stop the smell?

Only when diet or stool quality contributes. Food cannot treat an abscess, diseased tooth, yeast infection or urinary disease.

Is fishy odor always an emergency?

No, but pain, swelling, pus, blood, weakness, fever or inability to defecate or urinate requires prompt care.

Trusted sources

• Merck Veterinary Manual: anal sac disease
• Merck Veterinary Manual: periodontal disease
• Merck Veterinary Manual: vaginitis

This guide is educational. Persistent odor needs its source identified, particularly when pain, discharge, swelling, dental or urinary signs are present.