The Fish Oil Mistake Most Aussie and UK Cat Owners Are Making

Why opened fish oil bottles can go stale within weeks — and what many cat owners only realise after their cat starts refusing it.

Updated 2 May 2026

Read time: 4 mins

Written by Sarah Whitmore

Pet Wellness Consultant

When Our Happy Days Started to Fade

I noticed it on a Tuesday in March.

 

My nine-year-old tortie, Pepper, was on the kitchen bench — her usual spot, the one she's not technically allowed on — and the morning light caught her coat in a way that made me put the coffee down.

 

She looked dull. Not unwell. Just off. The shine was gone. There was a flaky patch behind her ears. And when she jumped down, there was a stiffness to the landing that hadn't been there a year before.

 

I booked a vet appointment for that afternoon.

What I learned over the next three weeks ended with me throwing out a £30 bottle of fish oil I'd been religiously giving her for eight months. I want to share it in case you're giving your cat fish oil too.

What nobody mentions on the bottle

My vet didn’t tell me to stop giving Pepper omega-3.

 

She told me the opposite — that for a cat Pepper’s age, with her coat and joints, omega-3 was one of the most sensible supplements I could be giving her.

 

The problem, she said, wasn’t the omega-3.

 

It was what happens to it the moment you open the bottle.

 

Fish oil oxidises. Fast.

 

The second oxygen hits the oil, a clock starts. Within weeks — sometimes days, depending on how it’s stored — it begins going rancid.

 

We can’t always smell it.

 

Cats can.

 

They’re built to detect spoiled fat. It’s a survival thing.

 

“That’s why so many cats eat fish oil happily for the first week and then suddenly refuse it,” my vet said. 

“The cat isn’t being fussy. The oil may have started to turn.”

And rancid oil isn’t just less effective.

 

Oxidised omega-3 can produce compounds that work against the very reason you bought it in the first place.

 

I sat there thinking about the bottle on my kitchen counter. In summer. Near the kettle.

 

Months of doing the right thing the wrong way.

 

I felt stupid, honestly.

 

I read ingredient lists on my own cereal. But I’d been pouring slowly-going-rancid oil onto my cat’s food because the bottle looked premium and came from a brand I recognised.

The format problem

Once I started looking into it, I realised most cat fish oils have the same flaw.

 

They’re sold in bottles.

 

That means every time you open the cap or press the pump, more air gets in. The oil sits there for weeks. Sometimes months. And by the end of the bottle, what your cat is eating may not be the same quality as what they ate on day one.

 

That also explains why so many cats seem to “go off” fish oil.

 

They may not be rejecting omega-3.

 

They may be rejecting stale oil.

 

That was the part nobody had explained to me.

The alternative I found

My vet mentioned, almost as an aside, that some Australian animal nutrition researchers had helped develop a different format: single-serve fish oil sachets designed specifically around the oxidation problem.

 

The brand is called Fureeze.

 

I hadn’t heard of them before. They weren’t in the big pet chains I usually shopped from. But the idea made immediate sense.

 

Instead of one bottle being opened again and again, each dose comes sealed in its own sachet.

 

So the oil doesn’t meet oxygen until the moment you tear it open and squeeze it onto your cat’s food.

 

Day one freshness. Day twenty-eight freshness.

 

No fridge smell. No sticky pump. No guessing the dose. No bottle slowly going off on the counter.

 

→ See the Fureeze Daily Fish & Krill Oil Supplement

Why the formula stood out

The format was what got my attention.

 

Most cat fish oils use one source — usually salmon oil or generic fish oil.

 

Fureeze uses a blend of anchovy oil and Antarctic krill oil.

 

Anchovies sit lower on the food chain, which generally means lower heavy metal risk compared with larger fish.

 

Krill oil is different because its omega-3 is bound to phospholipids, which are easier for the body to use. It also naturally contains astaxanthin, an antioxidant that boosts immunity of cats.

 

Then there are the extras.

 

Taurine for heart and eye function.

 

A live probiotic strain to support digestion and absorption.

 

Nothing in it felt random. Every ingredient seemed to have a reason for being there.

 

They also tested whether cats would actually eat it.

 

In a double-blind palatability trial with 100 domestic cats, Fureeze was chosen first 91% of the time against major bottled fish oil supplements.

 

You can argue with marketing claims.

 

Cats refusing their food is harder to argue with.

What happened with Pepper

I started Pepper on Fureeze in early April.

 

Week one, nothing dramatic.

 

She ate her food with the sachet mixed in straight away, which was already a good sign because she’d been getting increasingly suspicious of her old fish oil.

 

Week two, the flaky patch behind her ears had cleared.

 

By the end of week three, the dullness had lifted.

 

Not some overnight miracle. Just softer, glossier, healthier-looking fur. The kind of low-grade shine healthy cats have and tired-looking cats don’t.

 

My partner noticed before I said anything, which felt like the real proof.

 

By week six, she was jumping onto the kitchen bench with a fluidity she hadn’t had in a long time.

Whether that was the omega-3 helping her joints or just her overall health improving, I can’t say for certain.

 

But she’s nine.

 

And she’s moving more like she did a few years ago.

 

I switched to subscription after the first box. I’d been spending more on bottled fish oil anyway, and this was cleaner, easier, and Pepper actually ate it.

What Aussie and UK cat parents are saying

⭐⭐⭐⭐⭐ "My vet asked what I'd changed in my cat's diet. Said first thing — this." 

— Michael C., Verified Buyer

 

⭐⭐⭐⭐⭐ "Pre-portioned, no mess, no refrigeration needed — finally a supplement that's actually convenient. Won't be going back to liquid fish oil." 

— Sarah M., Verified Buyer

 

⭐⭐⭐⭐⭐ "I have two cats and a dog, so I need something practical. One sachet each, no measuring, no arguments about who got more." 

— Priya S., Verified Buyer

 

Reviewed at 4.7/5 across 2,500+ verified Aussie and UK customers.

If you’re already giving your cat fish oil

You’re probably trying to do the right thing.

 

But the format matters more than most brands want to admit.

 

A fresh-sealed daily dose that your cat eats consistently will beat a premium-looking bottle that starts oxidising after opening.

 

Every time.

 

Fureeze sells direct on their website. Each pack contains 28 sachets — a four-week supply for one cat.

 

It’s Australian owned, doesn’t need refrigeration, and comes with a 90-day money-back guarantee if your cat won’t eat it.

 

The subscription option also drops the per-sachet cost if you set it up monthly, and you can cancel any time from the customer portal.

 

If you’ve been doing the bottled fish oil thing and it hasn’t really worked, this is the version I wish I’d found sooner.

 

→ Try Fureeze Daily Fish & Krill Oil Supplement

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Sarah Whitmore is a UK-based writer and lifelong cat owner. This article includes affiliate links; Fureeze provided product for review but did not approve the final copy. Always consult your vet before introducing a new supplement, especially if your cat is on medication, has pancreatitis, or is pregnant.

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