Whole raw fish vs fish oil for dogs: What's the difference?

Table of Contents

Most raw feeders use fish oil to add Omega-3s — but it doesn’t cover everything your dog actually needs.

Whole oily fish delivers both Omega-3 fatty acids and naturally occurring vitamin D in one ingredient, while fish oil only supplies Omega-3s — which is why relying on oil alone can leave a nutritional gap.

So no, whole raw fish and fish oil are not interchangeable in raw feeding.

I’ve been raw feeding my dogs since 2015 and started making my own raw dog food in 2016. Like most raw feeders starting out, I began with fish oil.

It’s beginner-friendly, easy to portion, easy to store, and simple to add to any meal.

The main reason for using fish oil is to balance the ratio of Omega-3 to Omega-6 fatty acids.

Most cuts of meat from land animals — like beef, lamb, and chicken — are naturally higher in Omega-6s than Omega-3s. When those animals are raised on grain-heavy diets, that imbalance becomes even more pronounced.

Fish oil does exactly what it’s supposed to do — it delivers Omega-3 fatty acids (EPA & DHA).

But when it comes to vitamin D, the picture changes.

To put this into perspective, 100 g of whole herring can provide anywhere from ~700 to over 1,500 IU of vitamin D — while fish oil typically provides little to none.

Vitamin D levels in fish vary based on fat content, diet, whether the fish is wild-caught or farmed, and whether you feed the whole fish or just parts of it. When you feed whole fish, you’re getting vitamin D from both fat and organs — in its natural context.

Over time, as I became more intentional with how I built my dogs’ bowls, that approach shifted.

Once I started feeding Omega-3-rich cuts like brains and eyes, I moved away from relying on fish oil and transitioned to mostly feeding whole oily fish.

Because here’s the key difference:

Whole fish doesn’t just deliver nutrients — it delivers the whole animal.

That means your dog gets Omega-3s and vitamin D, plus:

micronutrients from organs like the brain and eyes
the natural structure of the food
and the physical act of chewing, which supports jaw strength and mental enrichment

Fish oil, on the other hand, is a concentrated extract. It serves a purpose — but it removes everything else that comes with feeding the fish itself.

In this article, I’ll walk you through:

how whole raw fish and fish oil compare nutritionally
when fish oil makes sense (and when it doesn’t)
how vitamin D and vitamin E play into both options
and why plant oils like hemp, rapeseed, and linseed aren’t true substitutes

So you can choose the option that actually fits your dog — and understand exactly what you’re adding to the bowl.

Raw dog food bowl with whole oily fish alongside fish oil supplements, comparing whole raw fish versus fish oil for dogs

Why Whole Raw Fish Is My First Choice

When you feed a whole fish, you’re not just adding Omega-3s.

You’re feeding an entire animal — and that changes everything.

Whole raw fish provides:

Jaw exercise and mental enrichment
Omega-3 fatty acids (EPA & DHA)
Naturally occurring vitamin D
High-quality protein
Micronutrients from organs like the eyes and brain
Small amounts of vitamin E
Fiber from fins and connective tissue

That last point matters more than most people realize.

A dog crunching through a whole mackerel uses their jaw, neck, and chewing muscles very differently than a dog swallowing oil mixed into a meal. Larger fish heads like salmon heads give dogs a nice workout, too!

Smaller fish like sardines, sprats, or anchovies still count — just with less of a workout.

Omega-3s – Why Your Dog Actually Needs Them

Omega-3 fatty acids for dogs aren’t just “nice to have.”

They:

• Help balance the high Omega-6 content of poultry and ruminant meats like beef and lamb
• Support healthy skin and a shiny coat
• Help reduce inflammation
• Promote brain health
• Support joint health and mobility

Most raw diets naturally skew high in Omega-6.

Omega-3s help bring that ratio back into balance — which is why fish plays such an important role in raw feeding.

Vitamin D: The Often-Overlooked Nutrient

Vitamin D is critical for dogs and is frequently under-supplied.

It supports:

calcium and phosphorus regulation
bone health and skeletal development
immune function
muscle strength and neuromuscular signaling

Whole fish is one of the most natural dietary sources — but vitamin D content varies by species.

This depends on:

fat content
diet (plankton-rich feeding)
wild vs farmed
whole fish vs fillet

This is why rotating oily fish like herring, mackerel, and sardines helps create a more balanced intake over time.

Vitamin D Levels in Common Whole Fish (High → Lower)

So now we know that not all oily fish provide the same amount of vitamin D, and here’s how common whole fish compare:

Herring – very high in vitamin D
Sprats – high, similar to herring
Mackerel – high, especially whole
Sardines – moderate
Anchovies – lower, mainly an Omega-3 source

This matters because fish oils are typically processed to concentrate Omega-3 fatty acids, not vitamin D. During processing, vitamin D levels are often reduced or become inconsistent, which is why most standard fish oils don’t meaningfully contribute to vitamin D intake.

When you feed whole fish — especially vitamin-D-rich species like herring or mackerel — you’re naturally covering two critical needs at once: Omega-3s and vitamin D. That’s something fish oil alone usually can’t do.

This is also why rotating different oily fish is beneficial. Just like with protein rotation, variety helps balance nutritional differences between species and reduces the risk of over- or under-supplying certain nutrients over time.

How Much Vitamin D Is in Whole Fish vs Fish Oil vs Cod Liver Oil?

Whole oily fish is one of the most reliable natural sources of vitamin D — while fish oil contributes little to none.

100 g whole herring → ~700–1,500 IU vitamin D
fish oil → negligible
1 tsp cod liver oil → ~400–1,000 IU

Cod liver oil contains vitamin D because it’s made from the liver — unlike standard fish oil.

This difference exists because vitamin D is stored in the fat and organs of the fish — especially the liver.

When you feed whole fish, your dog gets vitamin D in its natural context, alongside fats and other nutrients that support absorption.

Fish oil, on the other hand, is processed specifically to concentrate Omega-3 fatty acids (EPA & DHA) — not vitamin D. During processing, vitamin D is largely removed or becomes inconsistent, which is why it’s not considered a reliable source.

Cod liver oil sits somewhere in between.

Because it’s made from the liver of the fish, it naturally contains vitamin D (and vitamin A), which makes it a useful tool when whole fish isn’t being fed regularly.

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Vitamin E: The Balancing Nutrient Many People Miss

Omega-3 fatty acids don’t work in isolation.

The more Omega-3s you add to your dog’s diet — especially through fish oil — the more vitamin E your dog needs.

That’s because vitamin E protects fats from oxidative damage. Without enough of it, those highly sensitive Omega-3 fatty acids can oxidize in the body instead of doing their job.

Vitamin E supports:

cell protection and immune health
healthy skin and coat
muscle and nerve function
protection against oxidative stress

But here’s where this becomes important in practice:

Fish oil increases your dog’s need for vitamin E — without reliably supplying it.

Some high-quality fish oils include added vitamin E for this exact reason — but many don’t.

If you’re using fish oil, always check the label.
If there’s no vitamin E added, I wouldn’t use that product.

Technically, you can add vitamin E separately in drop form. But at that point, you’re stacking multiple supplements just to make one ingredient work — and that’s where raw feeding starts to feel unnecessarily complicated.

Whole fish, on the other hand, naturally contains small amounts of vitamin E and delivers it alongside fats in a complete food matrix.

That said, whole fish doesn’t fully cover vitamin E needs on its own — especially if you’re feeding higher amounts of Omega-3s.

In a balanced raw diet, vitamin E comes from a combination of different foods over time, not just one ingredient. Whole fish gets you closer to that natural balance, but overall variety still plays an important role.

If you’re not feeding whole fish regularly, vitamin E can also come from other natural sources like:

egg yolks
fatty cuts of meat (especially grass-fed beef and lamb)
organs like liver and kidney
small amounts of plant-based ingredients like wheat germ oil or sunflower oil

In practice, this is where context matters:

If you’re feeding whole oily fish at around 10% of your dog’s overall intake — or a few times per week — you’re typically not pushing Omega-3 levels high enough to significantly increase vitamin E requirements.

But once you start going beyond that — or adding fish oil on top — vitamin E becomes much more important to pay attention to.

Still, the key takeaway is this:

The more Omega-3s you add, the more you need to think about vitamin E.

This is another reason why whole fish is often the more complete option — while fish oil requires more intentional balancing.

Fish Oil: What It Does — And What It Doesn’t

Fish oil is a practical alternative when whole fish isn’t an option.

It is:

a concentrated source of Omega-3s
easy to portion and store
consistent to feed

But it has limitations.

It does not provide meaningful vitamin D and increases the need for vitamin E.

If you rely on fish oil, vitamin D must come from another source — typically whole fish or cod liver oil.

Cod Liver Oil vs. Fish Oil: Same Category, Different Purpose

Cod liver oil and fish oil are often lumped together, but nutritionally, they serve different roles in a raw diet for dogs.

Fish oil is primarily used as a source of Omega-3 fatty acids (EPA and DHA). Most fish oils contain little to no vitamin D and are best viewed as an Omega-3 supplement that needs to be balanced with attention to vitamin E and vitamin D elsewhere in the diet.

Cod liver oil, on the other hand, comes specifically from the liver of cod. In addition to Omega-3s, it naturally contains vitamin D and vitamin A, which makes it a more nutrient-dense but also more potent supplement.

Because of this, cod liver oil isn’t simply a “better fish oil.”

It’s a different tool.

It can be useful when vitamin D is missing from the diet, especially if whole fish isn’t being fed regularly. At the same time, it requires careful dosing, since vitamin A and vitamin D are fat-soluble vitamins that can accumulate if overused.

In practice, fish oil is often used to support Omega-3 intake, while cod liver oil is used more strategically to help cover vitamin D needs — not as a daily Omega-3 replacement.

A Quick Note on Vitamin A

Cod liver oil is naturally high in vitamin A — just like liver itself.

Because of this, when you use cod liver oil regularly, you don’t need to feed additional liver at the same time, since both supply vitamin A. Stacking multiple vitamin-A-rich sources can increase the risk of oversupplying this fat-soluble vitamin.

This is another reason cod liver oil should be used intentionally and with an understanding of what it replaces in the diet. It’s not just an Omega-3 supplement — it overlaps nutritionally with liver and should be factored into the overall feeding plan.

A Note On Plant Oils (Hemp, Rapeseed, Linseed)

Plant oils often come up as alternatives, but they’re not nutritionally equivalent to fish.

Plant oils provide ALA (alpha-linolenic acid) — not EPA and DHA.

Dogs can convert ALA into EPA and DHA, but very inefficiently.

Oils like:

Hemp oil
Rapeseed (canola) oil
Linseed (flaxseed) oil

can support skin and coat health, but they do not replace fish or fish oil for inflammation control, joint support, or brain health.

Think of plant oils as supportive fats, not Omega-3 replacements.

The Bottom Line: Whole Fish First, Oils As A Tool

When it comes to adding Omega-3s to a raw diet, my first choice is whole oily fish.

It covers both Omega-3 fatty acids and vitamin D in one ingredient — while also providing additional nutrients and the benefits of chewing.

Rotating between fish like herring, mackerel, sardines, and sprats helps balance nutrient differences and keeps your dog’s diet varied.

That said, whole fish isn’t always practical.

Fish oil is a useful tool when used correctly — but it requires more intentional balancing, especially when it comes to vitamin D and vitamin E.

There’s no single perfect approach.

The goal is to understand what each option provides — and choose what works best for your dog and your routine.

FAQs: Whole Fish vs Fish Oil for Dogs

Is fish oil enough for dogs on a raw diet?

Fish oil is not enough on its own. It provides Omega-3 fatty acids (EPA & DHA), but it does not supply meaningful amounts of vitamin D and increases your dog’s need for vitamin E. If you rely on fish oil, you need to account for those nutrients separately.

Is whole fish better than fish oil for dogs?

Whole oily fish is generally the more complete option because it provides Omega-3 fatty acids, naturally occurring vitamin D, and additional nutrients from organs and connective tissue. It also supports chewing and mental enrichment, which fish oil cannot offer.

Does fish oil contain vitamin D?

No, standard fish oil does not contain meaningful amounts of vitamin D. It is processed to concentrate Omega-3 fatty acids, not fat-soluble vitamins. If vitamin D is needed, it must come from whole fish, cod liver oil, or another source.

Do dogs need vitamin E when taking fish oil?

Yes. The more Omega-3 fatty acids you add to your dog’s diet, the more vitamin E is needed to protect those fats from oxidation. Many high-quality fish oils include added vitamin E, but if they don’t, it should be considered separately.

How much whole fish should I feed my dog?

A practical guideline is to feed whole oily fish at around 10% of your dog’s total intake or a few times per week. At this level, Omega-3 intake is beneficial without significantly increasing vitamin E requirements.

What’s the difference between fish oil and cod liver oil?

Fish oil is primarily a source of Omega-3 fatty acids. Cod liver oil also provides vitamin D and vitamin A because it comes from the liver. It’s used more strategically to support vitamin D intake, not as a direct replacement for fish oil.

Can plant oils replace fish oil for dogs?

No. Plant oils like hemp, flaxseed, or rapeseed oil provide ALA, which dogs convert very inefficiently into EPA and DHA. They can support skin and coat health but do not replace fish or fish oil.

Whole Raw Fish vs. Fish Oil for Dogs: What’s the Difference?