Should my cat be on an only fish diet?

No, it's not true that cats should only eat fish. While fish can be part of a cat's diet, it shouldn't be the only food they eat. Here's why:

1. Nutritional Balance: Cats require a balanced diet just like humans do. This means they need a variety of different nutrients, many of which come from different types of food. Just feeding a cat fish can result in deficiencies in certain nutrients, such as taurine, an essential amino acid for cats that is found in high quantities in muscle meat (like poultry or beef), but not as much in fish.

2. Mercury and Other Toxins: Fish, especially larger and predatory fish, can contain high levels of mercury and other toxins. While occasional consumption may not pose a risk, consistent consumption can lead to mercury poisoning in cats.

3. Thiamine Deficiency: Raw fish contains an enzyme called thiaminase, which destroys thiamine (vitamin B1). Cats eating large amounts of raw fish can develop a thiamine deficiency, which can cause serious health issues such as loss of appetite, seizures, and even death.

4. Fish Allergies: Some cats can develop allergies to fish, leading to gastrointestinal upset, skin issues, or other health problems.

5. Addiction: Many cats love the taste of fish, and if they eat it too often, they may refuse to eat other types of food. This can lead to a very unbalanced diet.

It's usually recommended to feed cats a balanced commercial cat food that has been formulated to meet all their nutritional needs. If you want to feed your cat fish, it should be thoroughly cooked (to kill parasites and deactivate thiaminase), and it should only make up a small portion of their overall diet. As always, it's a good idea to consult with your vet about the best diet for your individual cat.