The cats eat a fish so long and they had eaten so much that it is simply impossible to check, if it can harm cats. Actually fish is a very valuable source of the protein for a cat. But, as it is not surprising, cats can have some gastric disturbance, provoked by the usage of fish in nutrition.
At the first, many sorts of fishes in crude kind contain a lot of enzyme of a thiamine, which kills vitamin B1 (Thiamin), which is contained in other products. The loss of appetite, nervous breakdowns (vertigo, shiver, convulsion) can be the results of the lack of B1. The hot processing of the fish kills the great number of enzyme.
Secondly, at the use of a contaminated crude fish, caught in definite places, the special pathogenic microbes can be brought into the organism of a cat. For example, Dilphyllobothrium la tum is contained in a freshwater fish, which is caught near of Northern Ireland, and both trout and salmon from the northwest areas of Quiet Ocean near Northern America contain bacteriums, which provoke the " poisoning by salmon ". The freshwater rivers of Northern America and Southern Africa contain pulmonary trematodes Paragonimus kellicotti. Crude liver of some marine fishes contains materials, which can damage the nervous system.
In fluvial water and in seawater, contaminated by industrial and agricultural waste, in organisms of fishes can be the toxicants. The usage of the crude and cooked fish for the nutrition can be the reason of poisoning by pesticides, herbicides and heavy metals (Hydrargyrum, Cadmium).
The nutrition, poor by vitamin E and rich by unstable polyunsaturated Adepses, can provoke the " illness of yellow Adeps ". In that case any pressure on a skin provoke the pain, the reason of the cat's trying to run away. More often it takes place because of the usage of a great number of tinned red tunny, or (less frequently) of other sorts of fish (especially greasy) in nutrition.
Nowadays the one disease, which was known as the result of the usage of fish in nutrition at earlier times, can't harm to your pet. The speech goes about the variety of a dermatitis, which was called " the fish eczema". Getting down to business we can tell, that the arising during the illness of any blisters and, later, crusts, are consequents of pediculation ("a pedicular allergic dermatitis").