Clownfish Are Shrinking, Signaling Rising Ocean Temperatures

If the movie Finding Nemo were made in 2025, Nemo and his father Marlin would need to be scaled down in size, according to a study that took place in 2023. That's because clownfish, the specific species that Nemo and Marlin belonged to, have been shrinking in size thanks to the increasing water temperature in the ocean.

According to the study, the clownfish shrink in size due to heat stress, which requires them to become more physically efficient in order to survive their changing environment.

So, what does this mean for the beloved Nemos of the world? Keep reading to find out more.

The findings of the 2023 study were published on May 21, 2025, in the journal Science Advances. In the report, researchers said that they were able to observe the clownfish that swam in the waters of Kimbe Bay in Papua New Guinea. According to them, the fish responded dramatically to an oceanic heatwave that took place during 2023, shrinking in size to deal with the heat.

The fish not only appeared to lose weight, but they also shrank in length by a few millimeters as well.

While they're not exactly sure how they do this, the prevailing theory is that the fish absorb their tissue and bone to make themselves smaller.

Researchers found that the shrinking wasn't a fluke. Instead, they reported that at least 75 percent of the fish observed during the study shrunk during the heatwave, with some of them undergoing the change more than once, giving researchers some surprising insights into what happens beneath the ocean's surface when the mercury beings to rise.

"Nemos can shrink, and they do it to survive these heat stress events," Dr. Theresa Rueger, a lecturer from Tropical Marine Sciences at Newcastle University told the BBC. "It's not just them going on a diet and losing lots of weight, but they're actively changing their size and making themselves into a smaller individual that needs less food and is more efficient with oxygen."

Along with the shrinking clownfish, the coral in the area also underwent a bleaching event, which happens when ocean temperatures rise to an degree that becomes incompatible with life, causing coral to expel the organisms (zooxanthellae) that live within them, according to the National Oceanic and Atmospheric Administration (NOAA).

While coral can survive these events, NOAA says that it puts a lot of stress on them, and makes them more susceptible to disease.

As temperatures continue to climb around the world thanks to climate change, other creatures both big and small are forced to adapt. According to the ABC News, creatures like marine iguanas have also been documented pulling a similar maneuver, where they will shrink in size during those El Niño events that cause warmer waters to flow into the areas of the Galapagos that they call home.

Scientists don't yet know the long-term effects that this shrinking will have on animals, nor what it will mean if temperatures don't decrease in the areas that cause them such heat stress to begin with. But, one thing is for sure, the rising temperatures of our oceans are making it harder for animals to survive in their current state, sending a clear message to humans that climate change truly is changing the landscape of our world.