Answer: Well, so much fish has been fed to cats so many years that it is difficult to believe that it could be harmful. Essentially fish is, of course, a valuable source of protein in the diet. But, perhaps surprisingly, there are some disorders of cats that can arise specifically from eating fish.
Firstly, several varieties of raw fish contain high level of the enzyme thiaminase which will destroy the vitamin B1 present in other foods in the diet. Eventually the lack of this vitamin could result in the cat losing its appetite and showing nervous signs. Cooking the fish destroys this enzyme.
Eating infected raw fish from certain areas can transmit specific disease producing organisms to cats: the tapeworm Diphyllobothrium Latium from the fresh water fish in, for example, Northern Ireland, and bacteria from the salmon and trout causing ‘salmon poisoning’ in the Pacific North-west of the America. Again in North America and South Africa the eating of the crayfish can transmit a lung fluke parafonisum kellicotti to the cat. And the livers of some marine fish contain substance which, if uncooked, will damage the nervous system.
In areas where the river water or sea water is heavily polluted with the agricultural or industrial wastes, toxic substance can become concentrated via of a food chain in the bodies of fish which are sometimes offered for sale. If eaten, raw or cooked, poisoning with herbicides, insecticides or one of the heavy metals could follow.
A diet deficient in vitamin E and reach in unsterilized polyunsaturated fat can result in the fat strong cells beneath the skin becoming inflamed. Pressure in the skin causes pain and so the cat naturally resent handling. The diet most commonly at fault is one containing large quantities of canned red tuna fish, but other fish, particularly oily varieties, and even large amount of horsemeat, are sometime responsible. However today, sufficient vitamin E is added to most commercial tuna fish products to prevent this disease occurring.
On the credit side, on disease properly thought to be due to feeding but now known not to be, is similarly dermatitis, or military eczema, previously called ‘fish eczema’ or ‘fish eater’ eczema. The multiple small skin eruptions, which eventually rupture producing crusty scabs accompanied by intense skin irritation, are in fact due to an allergic reaction to the bites of fleas.
