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Slime Molds Can Remember Things Without a Brain

A picture taken on October 16, 2019 at the Parc Zoologique de Paris shows a Physarum Polycephalum better known as a “Blob.”STEPHANE DE SAKUTIN | AFP | Getty Images
A picture taken on October 16, 2019 at the Parc Zoologique de Paris shows a Physarum Polycephalum better known as a “Blob.”STEPHANE DE SAKUTIN | AFP | Getty Images
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Slime Molds Can Remember Things Without a Brain

A picture taken on October 16, 2019 at the Parc Zoologique de Paris shows a Physarum Polycephalum better known as a “Blob.”STEPHANE DE SAKUTIN | AFP | Getty Images
A picture taken on October 16, 2019 at the Parc Zoologique de Paris shows a Physarum Polycephalum better known as a “Blob.”STEPHANE DE SAKUTIN | AFP | Getty Images

A recent German study found that the slime mold - known as Physarum polycephalum or The Blob - seems to remember where it previously found sources of food even without a brain or nervous system.

P. polycephalum is one of the most peculiar forms of life on earth. It is not plant, animal, nor fungus, but a species of slime mold which lives in dark forests and enjoys damp and cool environments.

The creature wanders over dead plants with a significant speed eating all fungi, bacteria, and decomposed materials it may find in its way.

Early in its life cycle, P. polycephalum exists as a single cell with a single nucleus, but later it merges with other cells to form a huge single cell that looks like a yellow pool of mud.

Similar to the invincible creatures featured in The Blob thriller, P. polycephalum can reassemble its parts even after being ripped in pieces.

In 2000, Japanese researcher Toshiyuki Nakagaki discovered that P. polycephalum was capable of solving a simple maze to reach a food source.

Biological physicists Mirna Kramar and Karen Alim of the Max Planck Institute in Germany have discovered that this brainless, neuronless creature uses the very architecture of its body to store memories about where it has previously found food.

The body of this creature is composed of a complicated network of connected tubes. During a study that will be published on March 9, in the PNAS journal, the biological physicists found that when P. polycephalum discovers a source of food, it releases a chemical that locally softens the tube wall at the site of the food.

This then triggers the tubes to dilate, becoming wider, to expedite flow within the slime mold to the site. When it found and eaten a nutritious meal, those thick tubes remain in place so that it can quickly return to the site if food were to reappear.

P. polycephalum can reabsorb parts of its body if it stretches out exploratory tubes into a region that is inhospitable, or contains nothing of interest.

"This is not utterly dissimilar to how the human brain works. In this case, synapses, which send information between neurons, strengthen when we learn and grow stronger the more we use them, but can grow weaker if we don't - vaguely similar to the slime mold's tubes, which will grow thicker at sites of interest, but will die off or be reabsorbed if their presence is no longer useful to the organism," said researcher Karen Alim in a report published on March 1, on the Science Alert website.

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Varieties

'Turkish Salmon': The Black Sea's New Rose-Colored Gold 

People work in a Turkish salmon processing company in Trabzon, on the Black Sea on June 11, 2025. (AFP)
People work in a Turkish salmon processing company in Trabzon, on the Black Sea on June 11, 2025. (AFP)
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'Turkish Salmon': The Black Sea's New Rose-Colored Gold 

People work in a Turkish salmon processing company in Trabzon, on the Black Sea on June 11, 2025. (AFP)
People work in a Turkish salmon processing company in Trabzon, on the Black Sea on June 11, 2025. (AFP)

Sitting in his spacious office with a view of the Black Sea, Tayfun Denizer smiles: his rainbow trout, raised in submerged cages, have made him a wealthy man.

"Our exports surged from $500,000 in 2017 to $86 million last year, and this is just the beginning," said Denizer, general manager of Polifish, one of the Black Sea's main producers of what is marketed as "Turkish salmon".

In its infancy just a decade ago, production of trout, which in Türkiye is almost exclusively farmed for export, has exploded in line with the global demand for salmon, despite criticism of the intensive aquaculture required to farm it.

Last year, the country exported more than 78,000 tons of trout raised in its cooler northern Black Sea waters, a figure 16 times higher than in 2018.

And it brought in almost $498 million for Turkish producers, a number set to increase but is still far from the $12.8 billion netted by Norwegian salmon and trout giants in the same year.

Russia, which banned Norwegian salmon in 2014 after the West imposed sanctions over its annexation of Crimea, accounts for 74.1 percent of "Turkish salmon" exports, followed by Vietnam with 6.0 percent, and then Belarus, Germany and Japan.

Stale Knudsen, an anthropologist at Norway's Bergen University and a specialist on Black Sea fishing, said Russia offered "an available market that was easy to access, near Türkiye".

For him, the "spectacular success" of trout is also down to Türkiye's experience and the technology used in farming sea bass and sea bream, a field in which it leads Europe.

Turkish producers have also benefitted from the country's large number of reservoirs where the fish are a raised for several months before being transferred to the Black Sea.

There, the water temperature, which stays below 18 degrees Celsius (64.4 Fahrenheit) between October and June, allows the fish to reach 2.5 to 3.0 kilograms (5.5-6.6 pounds) by the time they are harvested.

Last, but not least, is the price.

"Our 'salmon' is about 15 to 20 percent cheaper than Norwegian salmon," said Ismail Kobya, deputy general manager of Akerko, a sector heavyweight that mainly exports to Japan and Russia.

"The species may be different but in terms of taste, color and flesh quality, our fish is superior to Norwegian salmon, according to our Japanese clients," Kobya told AFP at Akerko's headquarters near the northeastern town of Trabzon, where a Turkish flag flies alongside those of Russia and Japan.

Inside, a hundred or so employees in long blue waterproofs, green head coverings and rubber boots behead, gut, clean and debone trout that has an Aquaculture Stewardship Council (ASC) certification for responsible farming practices.

"Over the last two years, many Turkish producers have moved to get those certifications," said Knudsen, though he does not believe such labels are always a guarantee of sustainability.

"I think the rationale behind that is not only to become more sustainable, but is more importantly a strategy to try to enter the European markets... where the Norwegians have some kind of control," he said.

In a 2024 study, researchers from a Turkish public institute raised concerns that "the rapid growth of the trout farming sector... led to an uncontrolled decline in the survival rate" of the fish.

Pointing to the "spread of diseases" and "improper breeding management", the researchers found that nearly 70 percent of the trout were dying prematurely.

Polifish, which also has an ASC certification, acknowledged a mortality rate of around 50 percent of their fish stocks, predominantly in the reservoirs.

"When the fish are small, their immune systems aren't fully working," said its deputy general manager Talha Altun.

Akerko for its part claims to have "reached a stage where we have almost no disease".

"In our Black Sea cages, the mortality rate is lower than five percent, but these are farming operations and anything can happen," Kobya said.

Visible from the shore, the fish farms have attracted the wrath of local fishermen worried about the cages, which have a 50-meter (165-foot) diameter, being set up where they cast their nets to catch anchovy, mackerel and bonito.

Mustafa Kuru, head of a local fishermen's union, is a vocal opponent of a farming project that has been set up in his fishing zone just 70 kilometers (45 miles) from the Georgian border.

"The cages block the movement of the fish and what happens then? The fish start leaving the area," he said, accusing the trout farmers of pumping chemicals into their "fake fish".

He said a lack of fish stocks in the area had already forced two boats from his port to cast their nets much further afield -- off the western coast of Africa.

"If the fish leave, our boats will end up going to rack and ruin in our ports," he warned.