Awareness, Cat Food

Is Fish Based Cat Food Bad For Cats? What About Fish Oil?

Is Fish Based Cat Food Bad For Cats?

Small amounts of fish meal added to cat food is safe. It is an excellent source of omega-3 fatty acids for cats. However, a diet exclusively high in fish can lead to nutrient imbalances and deficiencies, particularly if it lacks variety or if the fish is not properly supplemented with essential nutrients. Moderation and variety are key to a healthy cat diet.

Fish Based Cat Food Bad For Cats

Why Fish in Large Quantity is Bad for Cats?

Allergen for Cats

Fish in large quantities can be problematic for cats because it often contains unsaturated fats that can oxidize and decrease the shelf-life of cat food, potentially leading to deficiencies in vitamin E and other nutrients. Additionally, some cats can develop allergies to fish proteins, which can manifest as skin problems or gastrointestinal upset. Over-reliance on fish can also lead to an imbalance in the ratio of fatty acids and an excess of minerals like mercury, which can be harmful over time.

Allergen for Cats

Mercury Concentration Above Safe Levels

A 2016 investigation by researchers at the University of Nevada, Reno, assessed the presence of mercury in over 100 commercially available pet foods. The findings indicated that mercury levels in some pet foods exceeded the thresholds deemed “safe” for wildlife consumption. In particular, pet food varieties that included fish were more likely to contain elevated mercury levels.

The benchmark for safety in small animals was established at 70 nanograms per gram (ng/g) daily, and the researchers used a precautionary value of 100 ng/g as a level of concern for cat and dog consumption. It was noted that cat food generally had higher mercury concentrations than dog food, with levels ranging between 1 ng/g and 604 ng/g in the samples tested.

Predatory fish, such as tuna, sharks, and swordfish, were highlighted as having more significant mercury accumulations due to their position at the top of the aquatic food chain. These species consume smaller fish that may already carry mercury, resulting in a compounded increase in their mercury content.

Mercury Concentration Above Safe Levels


Fish-based diets, especially when fed in large quantities, have been linked to an increased risk of hyperthyroidism in cats. The high iodine content in certain types of fish can contribute to excessive thyroid hormone production. Over time, this can lead to an overactive thyroid gland, causing a range of symptoms from weight loss to severe metabolic disturbances.

Kidney Problems

Fish contains high levels of phosphorus, which, when consumed in excess, can be detrimental to cats with kidney issues. The kidneys are responsible for filtering out excess phosphorus, and in cats with kidney disease, the increased burden can exacerbate the decline of kidney function, leading to a more rapid progression of the disease.

Urinary Tract Infections

A diet heavy in fish can lead to an imbalance in the pH of a cat’s urine, making it too acidic or too alkaline, which can predispose them to developing urinary tract infections (UTIs) and urinary crystals. Cats with recurring UTIs or urinary crystals may require a carefully balanced diet to maintain urinary tract health.

Urinary Tract Infections


Cats can become fixated on the taste of fish, leading to what is colloquially known as ‘fish addiction.’ This may result in a cat refusing to eat other types of food, which can lead to nutritional imbalances if the fish-based food does not provide all the necessary nutrients or if the cat consumes it to the exclusion of variety in their diet.

Types of Fish Commonly used in Cat Food and how they are bad for Cats


While salmon is often used in cat food due to its high omega-3 fatty acid content, it can sometimes contain environmental toxins like PCBs, especially if it is farmed. Excessive salmon consumption could also lead to obesity due to its high-fat content, and improperly prepared salmon poses a risk of parasitic infections.


Tuna is rich in protein and omega-3s but is also known for its higher mercury content, especially in larger species. Cats that eat too much tuna can be at risk of mercury poisoning, and it may also lead to thiamine deficiency, as tuna contains an enzyme that destroys this essential B vitamin.


Tilefish are among the types of fish that can contain high levels of mercury and are often advised against in human diets for this reason. In cat foods, frequent consumption of tilefish could lead to the same issues as tuna, with potential mercury accumulation posing a significant health risk over time.

Also Read: Does Canned Cat Food Go Bad?

Is Fish Oil Safe for Cats?

Fish oil is generally safe for cats and can be beneficial when given in the appropriate dosages, as it is rich in omega-3 fatty acids, which can help reduce inflammation and support skin and coat health. It may also benefit joint health and cognitive function. However, it’s important to use fish oil supplements designed for pets, as those for humans might contain ingredients that are harmful to cats. Always consult with a veterinarian to determine the correct dosage and to ensure it is integrated safely into your cat’s diet.

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