Introduction
Fish is commonly believed to be a healthy, natural food for cats. In fact, many cat owners enthusiastically feed fish products to their felines. Canned tuna and salmon are extremely popular flavors among cat foods and treats. With its strong scent and flavor, fish is an appetizing source of protein that most cats find irresistible.
However, despite its appeal to cats and cat owners alike, feeding fish regularly can actually be harmful to cats’ health in a number of ways. While fish can be included sparingly as an occasional treat, it should not make up a significant portion of any cat’s diet. Several components and contaminants commonly found in fish can cause serious health issues for cats over time.
Allergies
Some cats are allergic to fish. According to Wag Walking (https://wagwalking.com/cat/condition/fish-allergy), the symptoms of a fish allergy in cats often include itchy skin, excessive licking of the skin, scabs, and gastrointestinal issues. An article by Hartz (https://www.hartz.com/cat-food-allergies-is-your-feline-sensitive-to-seafood) notes that cats with a fish allergy may experience persistent scratching, vomiting, and diarrhea after eating fish. A food allergy can develop over time after the cat has been regularly fed fish. Allergic reactions tend to occur shortly after the cat has consumed fish. Treatment involves eliminating all fish and fish products from the cat’s diet.
Mercury Poisoning
Fish contain mercury that builds up in cats when they eat too much fish over a long period of time which can lead to mercury poisoning in cats (https://www.dailypaws.com/cats-kittens/health-care/cat-conditions/mercury-poisoning-in-cats). Mercury toxicity is not common in cats, but it is possible for cats to develop organic mercury poisoning from consuming too much fish according to veterinary experts (https://now.tufts.edu/2014/01/27/concerns-about-mercury-poisoning-it-safe-give-canned-tuna-cats-treat).
Symptoms of mercury poisoning in cats can include loss of coordination, irritability, vision problems, dementia, muscle tremors, and digestive issues. In severe cases, mercury poisoning can cause kidney failure, respiratory failure, and even death if untreated. Cats showing neurological symptoms like twitching, tremors, or seizures should be evaluated by a veterinarian immediately to test for mercury toxicity.
Thiamine Deficiency
Fish contains an enzyme called thiaminase that destroys vitamin B1, also known as thiamine. Thiamine is essential for cats to convert food into energy and maintain proper neurological function. Feeding raw fish blocks the absorption of thiamine in the diet, leading to a deficiency (source). Cooking fish destroys the thiaminase enzyme, making it safer (source).
Symptoms of thiamine deficiency include:
- Loss of appetite
- Weight loss
- Vomiting
- Wobbly gait, incoordination, falling
- Low energy, lethargy
- Rapid heartbeat
- Dilated pupils
- Seizures
If untreated, thiamine deficiency can be fatal. Consult a vet immediately if your cat shows any concerning symptoms after eating raw fish (source). Thiamine supplements, diet change, and supportive care can treat deficiency.
Contamination Risks
Eating raw fish poses a higher risk of exposure to parasites, bacteria, and viruses compared to cooked fish (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8455362/). Common parasites found in raw fish that can infect cats include flukes, tapeworms, roundworms, and hookworms. Bacteria such as Salmonella and Escherichia coli are also risks with raw fish consumption. These organisms can lead to vomiting, diarrhea, dehydration, and other illnesses in cats if ingested.
Proper preparation and handling can reduce, but not completely eliminate, the risks associated with raw fish. Freezing or cooking fish before feeding can kill parasites and bacteria. However, some hardy organisms may still survive. Thoroughly cleaning surfaces and utensils that come into contact with raw fish is also important to avoid cross-contamination. Despite precautions taken during preparation and storage, there is no way to fully guarantee that raw fish is free of dangerous pathogens (https://cooperpetcare.com/can-cats-eat-raw-fish/). For this reason, most veterinarians recommend against feeding raw fish to cats.
Digestive Upset
Fish can be difficult for cats to digest properly. Cats lack the enzymes needed to efficiently process fish, according to The Shelter Medicine Program at the University of Wisconsin School of Veterinary Medicine. The high fat content and unique proteins found in fish can overload a cat’s digestive system.
Eating fish can lead to vomiting, diarrhea, and other signs of an upset stomach in cats. The unfamiliar proteins and fats trigger an inflammatory reaction in some cats’ gastrointestinal tract. Fatty fish varieties like salmon and tuna are especially likely to cause digestive upset.
Kittens may be particularly sensitive to fish-based cat foods. Diarrhea is common when transitioning kittens to fish flavors. Digestive issues are less likely in adult cats if changes are made slowly by mixing in small amounts of fish-based food.
Urinary Tract Problems
Fish may contribute to urinary crystals and stones in cats. The salts, minerals and amino acids in fish can lead to alkaline urine and formation of struvite crystals, which can aggregate into painful stones in the bladder or urethra (VCAAnimalHospitals.com). Struvite stones often require surgery for removal. Urinary crystals and stones are more common in male cats due to their narrow urethra.
Dehydration also exacerbates urinary tract issues in cats. Cats have a low thirst drive and don’t drink enough water on their own in many cases. Feeding a fish-based diet without encouraging additional water intake can concentrate the urine and promote crystal formation. Ensuring cats have access to plenty of fresh water can help dilute the urine and minimize crystal issues (PetMD.com).
Nutritional Imbalances
Fish heavy diets lack balance of amino acids, vitamins and minerals that cats require. Feeding cats predominantly fish can lead to nutritional deficiencies over time, even if eating high quality fish (Source 1). Fish is relatively high in moisture and protein but lower in fat, vitamins A, B, D, and E compared to other meat sources. This imbalance can become problematic long-term.
One key deficiency associated with fish is vitamin K, which plays an important role in blood clotting. Studies have shown signs of vitamin K deficiency in cats eating high amounts of fish like salmon and tuna (Source 2). Vitamin K is better supplied by meats like chicken, beef and organs.
Another nutrient cats may lack over time on a fish-heavy diet is thiamine. Thiamine deficiency can contribute to neurological problems in cats. However, a veterinary nutritionist notes a cat would have to eat fish at every meal for a prolonged time to become deficient.
The takeaway is fish should not make up the entirety of any cat’s diet. Incorporating other meat, organ and plant-based foods can help provide a more complete nutritional profile.
Safer Fish Options
While fish in general may pose risks for cats, some types of fish can be safer options if prepared properly. Fish like sardines, mackerel, and salmon tend to have lower mercury levels compared to larger, longer-lived fish. Just be sure to choose fish packed in water without added salt or oil. Furthermore, fish is easier for cats to digest when it’s cooked. Lightly cooking fish helps break down bones and makes it less likely your cat will choke. Cooking also kills bacteria and parasites that could make your cat sick. When serving cooked fish, remove all bones first. With the proper precautions, small amounts of fish like sardines or salmon can be an occasional treat for cats. But it’s still best to rely on cat food for the bulk of their nutrition.
Conclusion
In summary, there are several important reasons why fish can be bad for cats:
- Fish allergies are common in cats and can cause skin irritation and gastrointestinal upset.
- Fish contains mercury that can accumulate in a cat’s body and cause mercury poisoning over time.
- Fish lacks thiamine, an essential vitamin for cats that they cannot synthesize on their own.
- Raw fish risks contamination with bacteria, parasites, and toxins.
- Fish can cause digestive upset in cats due to their high fat content.
- The high mineral content of fish can lead to urinary tract problems in cats.
- Fish does not provide complete and balanced nutrition for cats.
While fish does pose some risks, well-cooked fish body meat (without skin/bones) in moderation or a complete cat food containing fish can be safer options. When it comes to your cat’s diet, focus on high-quality commercial cat foods, meat-based proteins like chicken, and speak with your vet about the ideal diet for your cat’s needs.
