FISHY BUSINESS: Why you shouldn’t be feeding too much fish

Fish is one of the most common ingredients there is out there in the Singaporean pet market right now. Or perhaps since forever. Fish is cheap, and fish is good for humans, right? If it is good for people, it must be good for pets too, right? If you’ll just take a look at the pet food industry today, you’d even find entire pet food lines build from one protein source: fish.

(Can’t say, I’d get sued! But you know lah, huh. Right? Right? *nudge nudge*)

(Non Singaporean readers– Please drop us an email at, and we’ll explain to you the little idiosyncrasies of Singaporean language: seemingly meaningless fillers like ‘lah’, hehe)


But alright now, kitties: paws up those of you who are tuna junkies!

*eyes 70% of the Singaporean cat population*

Tsk tsk!


Albacore tuna, one of the more commonly eaten tuna. You didn’t think we were talking about bluefin tuna, did you? (Picture source:

But before I begin, this this feed-less-fish rule applies to not just cats, but dogs as well.

1.) Fish is, well, fishy. And cats are attracted to strong-smelling foods; why do you think smelly green tripe is so well received even by cats? Smelly…anything will likely be warmly welcomed by a cat. And few fish registers higher on the stinkometre than the humble tuna.

Kitty eats tuna for 2 days. Kitty is offered chicken.

Why would kitty eat something that smells less appetizing? ‘Stinky’ has just become ‘normal’ to a cat. Not normal? No eat!


Someone’s not impressed with dinner. 

Moreover, cats tend to get addicted to a single protein source. If kitty will only eat tuna again and again because it won’t eat anything else that smells less aromatic, pretty soon it will refuse anything without tuna inside.

(Addictions can form with chicken too, by the way. Or rabbit. Or lamb, beef, or quail.)

2. Fish have high allergenic levels
According to Susan Wynn, president of the American Holistic Veterinary Medical Association, fish is one of the most common allergens for pets.

Now your pet can get allergic to any protein source, because any protein that is over-consumed over a period of time can cause allergies but fish is a big risk, because fish naturally contain high levels of histamine.

The Seafood Information Centre, started by the University of California, Davis Department of Food Science and Technology (whew, what a mouthful!) certain fish species have too-high rates of histamine levels. These include the mahi-mahi, tuna, and bluefish. Apparently, bacteria that is associated with histamine development naturally exist in the gut and gills of live saltwater fish.

According to, a food intolerance support group for people with allergies, canned and processed fish, especially, contains a much higher histamine level than fresh fish. Few people feed their pets fresh fish (I give them raw salmon slivers now and then when Dear Mummy is not looking, because she’ll scream at me– she thinks they ‘eat better than humans’…wait. They actually do. Brats!) so most of the fish they get is processed.

Naturally high levels of histamine + added histamine from breakdown of fish protein = Not Good News for your pet

If this is not bad enough, The Seafood Information Centre adds happily [interpretation mine], after a long description of how processing and increased temperatures can increase histamine levels, that even butchering and filleting techniques will affect the level of histamine found in fish.

(I just very recently learnt that the filleting of salmon also affects how the sashimi tastes, so a very skilled Japanese chef could produce tastier salmon sashimi than a novice chef even if they’d used the same fish! I  seriously did not, ever in my previous years, realise that the preparation methods affected so much–taste AND histamine levels!)


I’m sorry I just had to post this. SO. MUCH. TASTY-LOOKIN’ HISTAMINE! wahaha. I’d still eat the lot. (Source: 


But too much fish may cause your pet rashes like these. (Picture source: Pet webmd)
GEEZ! Typing this paragraph makes me feel itchy already. Hey—is that an itch you feel on your thigh too? At this very moment? 😛

Pssst: Fish oil is okay, because fish oil is not protein.

Psssssst: Feeding too much raw fish to your pet will interfere with the absorption of thiamin (Vitamin B1) because of the presence of thiaminase but the cooking of fish destroys thiaminase.

Eh, for a non-itchy-scratchy-pet, just don’t feed fish often, okay?

3.) Foods containing fish is often high in magnesium and phosphorous.

Fish is often processed whole, bone, fins, tail and all, so that increases the level of magnesium and phosphorous in the processed food. Feeding too much fish, or fish on a regular basis, will increase your pet’s risk of developing Urinary Tract Infection and bladder stones. Not fun.

Male cats, especially, are more prone to UTIs.

4.) Vitamin K production.
Cats can produce their own vitamin K with most food sources, but fish may interfere with this ability.

According to—wait for it, another mouthful again!— Nutrient Requirements of Dogs and Cats By Subcommittee on Dog and Cat Nutrition, Committee on Animal Nutrition, National Research Council, studies of the effect of processed fish commercial diets (they used tuna and salmon) on cats in 1996 saw several queens and kittens dying of haemorrhage because of blood clotting problems.

The book also advises that many commercially-prepared foods (note: they did not say this was just about fish-based foods) do not add vitamin K.

5.) Increased risk of hyperthyroidism

There is an increased risk of hyperthyroidism from too much iodine consumption. There is plenty of iodine to be found in fish, so a steady diet of fish is again, bad news. Ron Hines, Doctor of Veterinary Medicine, suspects that this link between fish and hyperthyroidism is partially due to the low quality of fish found in fish-based foods, and as well as from the preservatives used to prepare these commercial foods. Moreover, the fish used to produce pet foods already contain too much iodine. Over a prolonged period of fishy feeding, we should not be surprised that these fishy junkie pets then develop hyperthyroidism.

images (1)

Sad-looking kitty with hyperthyroidism. (Source: Pet Webmd)

So if your pet is a fish junkie, what do you do?

1.) Try to change the type of fish you feed. You will probably lose the battle of wills with your pet (especially if it’s a tuna junkie cat), going cold-turkey will hurt your pet as well. Since top predator fish like tuna tend to have more toxins, try to switch to a fish that is lower in the food chain, such as sardine, which is also smelly, but less toxic.

2.) You can use the same method that people use to switch foods in their cats and avoid stomach upsets at the same time:
a. 90% tuna, 10% sardine, then
b. 80% tuna, 20% sardine, then
And so on, for a period over 1-2 weeks. Or more, if your pet proves to be especially stubborn.

3.) When tuna junkie pet has become accustomed to less tuna and more sardine, and then later on only sardine, you may want to introduce an even less aromatic fish: salmon, or tilapia.

4.) Slowly you may want to wean kitty, using the same method, off fish and onto something healthier, such as chicken, or rabbit.


You may want to avoid foods with such labels:

Ocean stew (anything with stew/basket/case/mix), or foods made with ocean fish, or foods that list ‘Ocean fish’ instead of specific fish type such as ‘sardine’ or ‘anchovy’ (do take note that some companies name any small fish ‘anchovy’.

In any case, ‘Ocean fish’ means nothing much. It has as much meaning as ‘all fish found in the ocean’! It tells you nothing, except that it supposedly came from the ocean. Yes. Go ahead and believe that.

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I am an ‘Ocean fish’ too! 

And please, rotate your foods! Rotate, rotate, rotate! If you rotate your food, there is less chance there is of your pet getting addicted to one food source.

Here’s to a non-itchy-scratchy pet! *toasts everyone*

Categories: Problems with commercial pet foods, The Raw Explorer

Tags: , , , ,

2 replies

  1. In Thailand, ALL the food is fish flavour, especially wet food. There’s tuna, mackerel and ocean fish – all Whiskas brand. What can I do?

    • Yikes Whiskas only…looks like you may have to buy from overseas and ship healthier food in yourself. We can send Wysong to Thailand though, and Know Better Pet Food (Better In The Raw) ships internationally. 🙂

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