Do Fish Have Blood? Facts You Never Knew

Fish – those slippery, scaled creatures that inhabit the watery depths of our oceans, lakes, and rivers.

We catch them for food, keep them as pets, and study their biology.

But how much do we really know about the inner workings of fish? One question that often gets asked is: do fish have blood?

In this article, we’ll dive below the surface (pun intended) and explore the circulatory system of our fishy friends.

We’ll find out if they actually have blood pumping through their veins and arteries like humans do.

We’ll also learn what color it is, whether they have blood vessels if it contains mercury, and more.

So join me as we tackle this subject head-on and get to the bottom of it. The water’s fine – let’s jump in!

Do Fish Have Blood?

Yes, fish do have blood. Just like humans and other animals, fish need a circulatory system to deliver oxygen and nutrients throughout their bodies in order to survive.

Fish have a two-chambered heart that pumps blood through the body and back to the heart in a single loop.

Oxygenated blood flows from the gills where it picks up oxygen, through arteries to tissues that need oxygen.

Deoxygenated blood then flows back to the heart through veins before being pumped back to the gills to get oxygenated again.

The blood of bony fish contains red blood cells, white blood cells, and platelets, all suspended in a watery plasma.

The red blood cells contain hemoglobin to transport oxygen, just like in humans. The plasma also contains minerals, proteins, and waste products the blood needs to transport.

So while fish live underwater and have some anatomical differences from humans, they do indeed have a circulatory system with blood that serves essentially the same functions as human blood.

You May Also Like – Do Fish Blink?

What Color Is Fish Blood?

The blood of fish comes in a few different shades depending on the species. In general, fish blood ranges from bright red to dark maroon or even light green.

The most common fish blood color is red, due to hemoglobin. Just like in humans, the hemoglobin protein in red blood cells contains iron atoms that bind to oxygen, giving it that distinct red hue.

This is seen in fish like trout, salmon, and goldfish.

However, some fish have blood that tends more towards green or greenish-blue. This includes primitive fish like hagfish and lampreys.

The blood stays this color even when oxygenated due to different heme proteins besides hemoglobin.

Cartilaginous fish like sharks have blood that runs from blue to purple to gray. Their blood gets this darker maroon/brown color from the protein hemocyanin which contains copper instead of iron.

You May Also Like – Can Sharks See in the Dark?

How Much Blood Do Fish Have?

The amount of blood a fish has depends on the size and species. But overall, fish have a much lower volume of blood compared to humans and other mammals.

Fish blood makes up between 2-10% of their total body weight.

For comparison, human blood comprises around 7% of our body weight. So a 10 lb fish likely has between 0.2 – 1 lb of blood circulating.

The lower blood volume in fish is simply because they are cold-blooded creatures.

Fish blood doesn’t need to regulate body temperature or transport as much oxygen to tissues as warm-blooded mammals. Therefore, their circulatory system doesn’t need to be as extensive.

Additionally, marine fish tend to have lower blood volumes around 2-4% of their weight. This allows their tissues to better absorb dissolved oxygen from the water.

Freshwater fish often have higher volumes around 5-10% to account for less oxygen in their environment.

So while a fish doesn’t need nearly as much blood pumping through its veins and arteries as we do, it still serves the vital functions of delivering nutrients and oxygen to organs and muscles.

The required blood volume fits the fish’s metabolism and habitat.

You May Also Like – Do Turtles Have Teeth?

Are There Any Fish Without Blood?

While most fish do have blood, there is one fascinating exception – the icefish. Icefish or white-blooded fish comprise the Channichthyidae family and live in the freezing waters around Antarctica.

These unique fish lack hemoglobin and red blood cells entirely. Instead of using hemoglobin to bind and transport oxygen through the blood, icefish rely on diffusion.

Their blood is essentially clear plasma, and they have enlarged gills and smooth skin that allow oxygen to directly diffuse into the bloodstream from the seawater.

Without red blood cells, icefish blood appears nearly transparent. This gives them a ghostly white coloration that contrasts starkly against the deep black seas they inhabit.

Scientists believe icefish evolved to survive without hemoglobin and red cells because the extremely cold waters surrounding Antarctica are highly oxygenated.

Therefore, their blood plasma is sufficient to diffuse and circulate enough oxygen throughout their body.

So while most fish species have red-blood cell-rich blood, the unique Antarctic icefish demonstrate that some fish can survive with clear, cell-free plasma.

It’s an amazing adaptation to their frigid underwater world.

You May Also Like – Do Seals Eat Penguins?

Is There Blood In Fish Meat?

When you eat a piece of fish, you may notice that the flesh lacks the red “bloody” color of meat like beef or chicken.

This raises the question – is there any blood at all in fish meat?

The answer is no, there is no blood present in the edible fillets and steaks of fish. Fish are slaughtered and processed in a way that removes all of their blood after catch.

Unlike mammals, fish blood doesn’t permeate throughout the muscle tissue.

It is contained mainly in blood vessels and capillaries, similar to humans.

So when processed, it’s relatively easy for all blood to be drained from the fish’s circulatory system.

The red liquid you sometimes see in raw fish packages is not actually blood.

It is a protein called myoglobin that helps supply oxygen to muscles. It’s released when the flesh is cut during processing.

Fish also have far less myoglobin compared to mammals, which is why fish meat appears white or translucent rather than red when cooked.

So you can be assured that fish fillets contain no blood. All blood is removed during slaughter and any liquid present is harmless myoglobin.

You May Also Like – Do Sharks Travel in Packs or Alone?

Final Thoughts

As we’ve learned, fish may seem very different from us humans on the outside, but inside they share a similar circulatory system complete with blood coursing through vessels and arteries.

While fish blood has some unique properties like color variation based on oxygen-binding proteins, it serves the same essential functions as human blood.

Oxygen and nutrient transport are just as vital to fish survival as they are to us terrestrial creatures.

Fish may have less total blood volume on average, but it is tailored to their cold-blooded metabolism.

And the rare icefish show that even without red blood cells, fish can adapt to thrive in frigid polar waters.

The bottom line is that just like us, fish need blood to live and thrive. Their blood may look different or have adaptations to aquatic life, but it’s still the life-giving fluid flowing through their veins.

Hopefully, this article answers the question of whether fish have blood.

Perhaps next time you catch a fish or order salmon for dinner, you’ll have a new appreciation for the vital fluid that powers its movements through the mysterious deep.

FAQs

Resources – (for further reading)

ScienceDirect – FISH BLOOD CELLS

Researchgate – Blood Volumes of Three Salmonids

Wikipedia – Mercury in fish

Jstor.org – Blood Types in Fish