Underwater creatures with regeneration ability (Part 2)

Underwater creatures with regeneration ability (Part 2)

In the last article (underwater creatures with regeneration ability Part 1), we saw the octopus that regenerates a broken wrist, the sea cucumber that loses its internal organs in a critical moment, the starfish that regenerates the whole body with a wrist, the conch that regenerates the eye-stalk, etc.

However, these aren’t the only creatures in the ocean that have super-regenerative abilities!

How about the regeneration mechanism of crabs, dolphins, sea squirts, zebrafish, and even sharks? Continue to deepen your knowledge by reading this article.


Regeneration of the crab is amazing
Image credit: Charlotte Harrison

Crabs will break their arms to survive when in danger. While running away, they easily removed one of their “legs” and left it as food for predators, then took the opportunity to escape.

Besides the reluctance to unload their legs in times of crisis, when crab claws are injured or necrotic, they will also take the initiative to abandon this physiological stress and then wait for new claws to slowly develop.

If the crab claws that no longer return their shells fall off, they will not grow back.


The regeneration and repairing ability of the dolphin is more advanced
Image credit: Yale Cohen

Let’s consider one of the biggest enemies of large mammals and dolphins in the sea, they are sharks.

Sharks often attack dolphins. Statistics show 70%-80% of the dolphins living in the waters near Australia have been bitten by sharks (cookie-cutter shark bite).

There are more injuries than the size of a basketball, especially shark teeth associated with harmful bacteria and microorganisms that can easily cause infections.

Such an injury is enough to kill people due to bleeding, but when it happens to dolphins, it will not be fatal and will not affect the condition of their skin.

They can in fact be treated such an injury without any external treatment. Under the circumstances, it will heal on its own within a few weeks without leaving any scars or after-effects.

First of all, dolphins rely on regulating the circulation of body blood flow and water pressure to stop bleeding.

They can reduce or even cut off their own blood flow to less important parts, such as injured places that help the blood to clot faster so that dolphins also dive into the deep sea to use the pressure of the outside water to reduce blood loss.

The skin and fat layer of dolphins contain natural antibacterial and anti-inflammatory substances, which can prevent wound infection.

The dolphin’s growth hormone can promote the production of stem cells.

These highly repairable stem cells can promote the rapid differentiation and growth of tissue cells, quickly repair damaged tissue, and complete wound healing within weeks.

The most amazing fact is that the animal usually feels pain after being injured and that can affect its behavior.

Dolphins have been seemed to feel obvious pain, but their fat layer appears to secrete a substance similar to morphine to relieve their pain.

It is observed that even though there is a large wound on the dolphin’s body, it has no significant pain response in their behavior and predatory ability.


Sharks cartilages also have a positive effect on cancer
Image credit: Simona Sergi

It is generally believed that the longer you live, the higher the risk of cancer in large organisms, as this means that more cells are at greater risk for genetic mutations and that a longer duration leads to more DNA damage and aging.

However, sharks that have existed on earth for over 400 million years have powerful genes, with an average lifespan of over 70 years, a large body, and at the top of the food chain, but they have an ultra-low cancer rate.

In 1992, Dr. William Lane published the book Sharks Don’t Get Cancer and How Shark Cartilage could save your life.

But the book concludes that shark cartilage (shark cartilage tablets) do not have a positive effect on cancer as a cure and that a large number of sharks die to create their product because the cure for this cancer has not been tested or proven.

Dr. Lance, the ‘father of shark therapy’, who first came to an appropriate conclusion, also admitted that the conclusion that sharks can fight against cancer is only based on a limited number of experimental results.

In fact, like other vertebrates, sharks can develop benign or malignant tumors, including cancer of the cartilage tissue.

Shark also have a different  regeneration strategy
Image credit: Romain Huneau

Scientists have discovered through genetic analysis of great white sharks that, compared to 23 pairs of human chromosomes, great white sharks have almost twice 41 pairs of chromosomes, meaning that some survival codes carried in the shark DNA is not available to humans.

400 million years of evolution has allowed sharks to have countermeasures to maintain the stability of their genome.

They are not as susceptible to cancer and senile diseases as humans. The consumption of shark products does not allow humans to have the ability of sharks to repair their own DNA.

Sharks can also heal wounds quickly. It was not until 1993 that people discovered that there is a natural coagulation dose in shark tissues, which promotes blood coagulation at the wound site, and a special substance-Squalamine, which can sterilize and resist viruses, and inhibit angiogenesis.

After the positively charged squalamine molecule enters the cell, it can specifically connect to the inner side of the negatively charged cell membrane like a button, and occupy the space of the positively charged protein that depends on the cell membrane during virus infection, thereby reducing the susceptibility of cells to viruses.


Ascidians are also one of the oldest species on the planet.

They are widely distributed in all oceans around the world and are shaped like plants, but in fact they belong to invertebrates and are very close to the earliest vertebrate ancestors 500 million years ago.

Ascidians have a hollow body with a layer of rucksack on the outside, also known as rucksacks.

In the early stage, ascidians had notochords, as well as visual organs, gill clefts, and tails.

However, the characteristics of these vertebrates disappeared one by one during the development process, which is called “retrograde metamorphosis” in biology.

Scientists have collected ascidian blood vessel to observe regeneration ability
Source: Yahoo.com

Scientists have collected ascidian blood vessel samples to observe the entire regeneration process of ascidians under a microscope.

The cells first gather into hollow spheres, then the cell layer folds inward and the organs gradually develop.

Two weeks later, they grow into adult ascidians with reproductive capacity.

Signals for other animals to trigger regeneration are transmitted from a central point, but ascidians can appear from many locations.

Obviously, the regenerative ability of ascidians is very strong. Even ascidians with only one blood vessel surviving can regenerate entire groups.

Such a powerful regeneration ability allows them to survive on the earth for 500 million years.


Zebrafish is a representative of vertebrates with strong self-healing and regeneration ability, which can regenerate tail fins, skin, heart, liver, and even photoreceptor cells and retinal nerves.

The gene sequences of zebrafish and humans have a high degree of similarity of 87% and have been widely used in life sciences and research in recent years.

When 95% of the caudal fin of an adult zebrafish is removed, the incision is quickly closed by epithelial cells that migrate from both sides, and the epithelial cells become thicker. Time can quickly regenerate a complete tail fin.

Regeneration mechanism of zebra fish
Image credit: Giorgia Beffanga

The heart regeneration mechanism of zebrafish also provides an important model for studying human heart cell regeneration.

After 20% of the zebrafish’s heart was removed, it did not affect their survival.

Hemorrhage followed by rapid coagulation, myocardial cells begin to proliferate in large numbers, and the heart was almost completely regenerated after 60 days.

Different from other higher organisms, the nerve tissue of zebrafish also has a strong ability to regenerate.

Through research on the regeneration of the retina, it is found that the retina and other nervous tissues of the zebrafish have been constantly undergoing metabolism of new and old cells throughout their lives.

When the retina is damaged, the stem cells are rapidly activated and begin to differentiate and proliferate all cell types to produce what that retina needs

Even after the spinal cord of zebrafish is damaged, it can immediately regenerate neurons and axons and restore spinal cord function.

Related article

Sharks will cure cancer

Read more

Underwater creatures with regeneration ability (Part 1)


Wang, S.-M & Wang, Y.-F & Li, Yong & Liu, J. & Li, Ligeng & Zhang, M.-L & Shi, Q.-W. (2016). Historical story on natural medicinal chemistry: Drugs from ocean.

Beffagna G. Zebrafish as a Smart Model to Understand Regeneration After Heart Injury: How Fish Could Help Humans. Front Cardiovasc Med. 2019;6:107. Published 2019 Aug 6.


Some photos of the article are from the Internet and Unsplash.com. If you have any copyright issues, please contact us.

Rajitha Dissanayake

Researcher in the field of Marine Mammals and Bio-acoustic

I'm a Master’s student in marine mammals and bio-acoustic laboratory, Institute of Deep-Sea Science and Engineering (IDSSE), Chinese Academy of Sciences (CAS) and focusing on the sustainable environmental application, conservation, and exploring all aspects of the ecology and behavior of marine mammals.

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