People generally assume that cats eating fish is perfectly natural; what cat doesn't like fish? Is there any real reason behind it? Actually, there are some things to know about cats eating fish. Ignoring these points could potentially lead to your cat contracting diseases it shouldn't.
There are many kinds of fish, which we will divide into two main categories: freshwater fish and saltwater fish. 
Let's talk about freshwater fish first. Freshwater fish is a relatively ideal food for cats. Although most of them have many bones, they don't pose a significant threat to a cat's digestive tract because most of the small bones are deflected by the barbs on a cat's tongue before being swallowed and digested in the stomach. The only thing to be careful about when feeding freshwater fish to cats is that the fish must be thoroughly cooked. Cats should never eat raw fish, especially the parts discarded during cooking, such as the head, gills, and internal organs. Never throw these parts to your cat carelessly.
Freshwater fish, especially those raised in natural waters and old ponds, may harbor a dangerous parasite—Cronobacter schistosomiasis. If a cat becomes infected by ingesting raw freshwater fish, the adult parasite will infest its liver, causing liver tissue damage. In the early stages, infected cats will exhibit loss of appetite and depression, followed by jaundice, vomiting, weight loss, and sometimes fever. If the owner is careless and fails to detect the infection promptly, it can endanger the cat's life.
There are generally three things to keep in mind when feeding cats saltwater fish:
First, saltwater fish generally have hard, large bones, especially those from fish like ribbonfish and yellow croaker that people often eat. These bones are very difficult for cats to chew and swallow. If the main bone is swallowed backwards, it can easily get stuck in the throat and be difficult to remove. Therefore, it is essential to remove the bones when feeding saltwater fish to cats.
Secondly, some cats are prone to urinary tract stones due to their individual constitution. The high magnesium salt content in saltwater fish can form stones in a cat's urinary tract. Therefore, cats with a history of urinary tract stones or a family history of this condition should minimize their consumption of saltwater fish.
Third, marine fish contain a large amount of thiaminase, which can break down thiamine in food and the body. If a cat's diet consists mainly of marine fish for a long period of time, it can cause vitamin B deficiency, leading to symptoms such as neck pain and inability to lift its neck.
Therefore, when feeding cats, the freshness of both freshwater and saltwater fish should be carefully considered. Fish is rich in protein, and once it spoils, it produces large amounts of histamine. Even if the fish is thoroughly cooked before feeding, the histamine will not be destroyed. Cats that ingest such fish may experience a range of allergic reactions, such as diarrhea, vomiting, itching on the ears and trunk, rashes around the ears and eyes, and sometimes even fur loss. These illnesses can last for varying durations, with severe cases potentially lasting up to a month. Owners should be vigilant to avoid unnecessary complications.
