Fish oil is rich in ω 3 unsaturated fatty acids, which is very beneficial to the health of cats. Here are some benefits of fish oil for cats:

1. Skin and fur health: Omega-3 fatty acids can promote cat's skin and hair health, relieve itching, dryness and shedding of skin, and make hair brighter.

2. Heart health: Fish oil can reduce the risk of heart disease in cats, because omega-3 fatty acids can help lower cholesterol and blood pressure and keep the heart healthy.

3. Joint health: Fish oil can lubricate the joints of cats, relieve the symptoms of arthritis and help prevent arthritis.

4. Immune system: ω 3 fatty acids can enhance the immunity of cats, help prevent diseases and improve health.

Therefore, if your cat doesn't eat enough fish oil, it may affect its health and longevity. You can feed the cat with pet food containing fish oil, or add some fish rich in omega-3 fatty acids, such as mackerel, mackerel, saury, salmon and so on. However, please note that if you are feeding your cat dry food, you may need to change it to wet food or homemade diet to ensure that your cat gets enough water and nutrition.