Why marine animals have different blood colour

The Spooky Seas programme is happening from 1 October to 15 November 2015. One of the activities is the Spooky Seas Adventure trail where you learn marine facts about spooky animals in the sea.


One of the stops at the trail is the Vampire’s Lair where you learn which marine animals have different blood colour. For those who haven’t visited the Aquarium yet, we bring the information to you on this blog.

Why some animals have different blood colour

Different protein in blood makes it appear in different colours. Human and most vertebrates have red-coloured blood because of the protein Haemoglobin which transports oxygen to tissues.

However, there are other animals with blood colour other than red. Let’s find out what other blood colours there are.

Here’s a handy graph from science blog Compound Interest about the chemistry of different colours of blood.

Marine animals blood colour

Graph source: Compound Interest

Blue-blooded animals

Octopus blood is blue because it contains a protein called Harmocyanin. The protein is responsible for keeping the species alive at extreme temperatures.

Most molluscs, such as squid and cuttlefish and arthropods like lobsters and horseshoe crabs, are also blue blooded.

Green-blooded animals

Tubeworms have green blood due to the protein Chlorocruorin, which is also found in many other marine worms. The deoxygenated blood containing Chlorocruorin is a light green colour while it is slightly darker green when oxygenated. In concentrated solutions, it is light red in colour.

Violet-blooded animals

Peanut Worms, and a few other marine worms, have violet blood because of the protein Haemorythrin. Peanut Worms can be found in mangroves on Singapore’s shores.

When carrying oxygen, Haemorythrin causes the blood to appear violet. However when deoxygenated, the blood is colourless.

Colourless blood

Ocellated Icefish blood is colourless as it has no oxygen-carrying proteins. Instead of using Haemoglobin to transport oxygen around their bodies, the Ocellated Icefish uses blood plasma to move oxygen in its body.


Learn more at Spooky Seas at S.E.A. Aquarium

Spooky Seas Vampire Lair S.E.A. Aquarium

Now that we’ve learned about the different blood colour in marine animal on the Spooky Seas Adventure Trail at S.E.A. Aquarium. Check out what other programmes are available during the special Spooky Seas programme, happening until 15 November 2015.

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