“90% percent of the world’s fisheries are fully fished or overfished. Overfishing, habitat destruction, and unsustainable catch practices are depleting marine life faster than can be replaced”. – Racing Extinction, 2015

Feeding our domestic cat is strongly associated with fish. The cliche portrait of the cat as a seafood lover is commonplace, like the image of the cat fishing in the goldfish bowl, the “tuna addict”, and back alley cats snatching fish scraps from trash cans. Countless pet products cater to this image with a wide variety of fish based and fish flavoured treats and staple diets.

Indeed, cats seem to fancy fish, and care givers around the world eagerly accommodate this desire, but because our domestic cats are a direct descendant of the African Wildcat of the Sub-Sahara, fish is not a natural food for them. All the physical attributes of our cats are fine tuned to hunting and eating small mammals. This fact has been documented by biologist very thoroughly.

The most up to date science of species classification based on molecular genetics as well as morphological schemes indicates that the domestic cat (felis silvestris catus – often called just felis catus) is one of four sub species of the species felis silvestris. Because domestication has largely influenced and grossly altered the domestic cat’s food preference, to explore the truly natural diet of felis catus we should look to the diet of its ancestors: the European wildcat or forest cat (felis silvestris silvestris), the Asian steppe cat (felis silvestris ornata), and the African wildcat or tawny cat (felis silvestris lybica) . When examining the diet of these three subspecies, none include fish. If we further expand our investigation to include all species of the genus felis, we come to the realization that only one of its members – the jungle cat (felis chaus) – includes fish in its diet, although still hunts predominantly rodent prey. None of the others members of the species do, including the black-footed cat (felis nigripes), the sand cat (felis margarita), and Chinese mountain cat (felis bleti).

Canned Tuna is among the most popular food stuff to feed to companion cats, because cats are very fond of it. It is not uncommon for cats who regularly receive tuna to refuse all other foods. Cats displaying this addiction-like behaviour are often referred to by Veterinarians as “tuna junkies”. Feeding a mainstay of canned tuna is long known to cause diseases of dietary origin. One of the most prevailing diseases afflicting “tuna junkies” is Steatitis or Yellow Fat Disease – an inflammation of the fat tissue in the body due to a deficiency of vitamin E. A vitamin E deficiency is usually the result of feeding tuna, or any canned fish, packed in vegetable oil. These products are high in polyunsaturated fatty acids which oxidate vitamin E, besides being a poor source of vitamin E to begin with. Currently, a diet consisting of large amount of any type of fish is considered the most common cause of this syndrome.

Canned fish– tuna or other, packed in water or oil – is not a complete diet for cats. Although it is high in protein, it does not supply the cat with sufficient amounts of certain amino acids, mainly taurine, to maintain health. Most canned fish does not provide the cat with enough Calcium to balance Phosphorus either, resulting in bone disease due to a deficiency of this mineral in the diet. Many essential vitamins are not provided in sufficient amounts through a diet of canned fish, such as vitamin A and most B vitamins, like Thiamin, Riboflavin. Pantothenic Acid, Folic Acid, and Vitamin B-12. Last but not least, most canned fish is high in sodium, possibly providing the cat with too much of this mineral.

Raw, whole fish: Much of the nutritional deficient nature of canned fish can be contributed to the way it was processed. Many nutrients are sensitive to heat, and cooking or canning reduces levels of or even eliminates some nutrients in foods. Also, many nutrients are concentrated in various organs and body parts – like vitamin A in liver and Calcium in bone – and carnivores are provided with a complete diet by consuming the entire prey. Therefore, would a diet consisting of whole, raw fish be adequate for cats? Many feral cats in the Mediterranean do indeed supplement their diet considerably with whole, raw fish, but unfortunately, no statistics are available about their health status.  Feeding raw, whole fish is not entirely without problems, however. An enzyme found in all raw fish, called thiaminase, can destroy vitamin B-1 (Thiamin), leading to neurological disorders accompanied by a general physical wasting due to loss of appetite. This enzyme can be destroyed by cooking the food, which however reduces overall nutritional density of the food itself as well. Raw, whole fish can also present a source of infection with parasites.

Fish, cooked or raw, as the meat base of a cat food recipe, like saltwater halibut and freshwater rainbow trout appear initially to be nutritionally adequate in all the essential amino acids and fatty acids. Supplementation could provide for correct amounts of Calcium within the right ratio with Phosphorus, and could bring levels of vitamins, such as vitamin A, D, E, and complex B, to optimal levels. However, fish meat seems to contain insufficient amounts of the trace minerals iron, zinc, copper, and manganese, making fish meat in the end an unsuitable choice as a base for a staple feline diet, because it would require unreasonable supplementation.

Although the majority of our feline companions seem to have a taste for things fishy, fish is not a natural food for them. Maybe it is the scent that makes these foods so appealing to felines, possibly triggering some craving, or it could be a learned taste preference. Many domestic cats raised in close contact with humans have exposure to fish from early on, predominantly through commercial foods containing fish meal as a protein source, as well as treats and table scraps. When raise without contact to fish as food, many cats will not eat fish when presented with it experimentally later in life. Maybe the stereotype teaches people that cats like fish, and people in turn teach cats to like fish. That cats don’t only make instinctive food choices, but also posses the ability to learn taste preferences is indisputable.

If fish is to be included in the meal plan of the domestic cat, it may be sensible to do so only as treats, supplements, or to entice a sick cat to eat. Other than that, the story of fish and cats should really be a fairy tale.

Last, but not least, fish as a food source has raised considerable ethical and environmental concerns in our modern times. Profit driven companies, including those who own pet food brands, and an ever growing global standard of living and growing human population literally emptying the oceans of life. The ocean ecosystem is at the point of collapse due to the activities of humans. The fishing industry has become largely unsustainable, and its practices are often unethical, and its treatment of its workers known to be unfair. Cats would not naturally eat fish, and they do not receive any benefit from eating it. Omitting it from the meal plan for cats will not deprive them of anything.