Kurage Wonder Member's Observation Log / Colored Jellyfish Edition

Kurage Wonder was established in 2020. Here you can encounter around 30 different types of jellyfish.
Jellyfish have a wide variety of characteristics. By learning about the highlights of each species, you may be able to find your favorite jellyfish.

Round jellyfish swimming around with a bouncy motion

Round, blue-bellied jellyfish are actively moving around in the tank. These adorable jellyfish are called colorful jellyfish.

The way it moves around restlessly, its umbrella pulsating constantly, makes you almost hear the sound "poyo poyo poyo poyo...!"

Because only blue individuals were once found, they were sometimes called blue jellyfish. Later, it was discovered that individuals of various colors, including brown and white, existed, and they are now called colorful jellyfish. They are a popular type of jellyfish due to their cute shape and vibrant colors.

Why are they so colorful? The secret of color.

So, we've learned that colorful jellyfish come in a variety of colors, including blue, brown, and white. When people see jellyfish of different colors in the same tank, they sometimes ask, "Are they different species of jellyfish?" This isn't surprising, as jellyfish of the same species generally tend to have similar colors. So, why do colorful jellyfish come in such a variety of colors?

The answer is... actually, we don't really know! There are many aspects of jellyfish ecology that remain unexplained, and this kind of thing happens quite often.

Colorful jellyfish are called rhizostome jellyfish. They belong to the same family as spotted jellyfish and upside-down jellyfish, and they have symbiotic phytoplankton called zooxanthellae living inside their bodies. It is thought that these zooxanthellae are the factor that determines their color, but the mysteries only deepen: when and how the color is determined, how they are differentiated at birth, and why they have multiple colors.

Dreaming of a "colorful" aquarium...

We've talked about the colors of jellyfish so far, but the Kyoto Aquarium only has blue jellyfish, so it's essentially a collection of blue jellyfish.

Most of the jellyfish at Kyoto Aquarium are born at the aquarium, and we obtain baby jellyfish by raising polyps (the anemone-like stage where fertilized eggs develop into larvae and attach to rocks, etc.). All of the color jellyfish that were born from the polyps we had turned blue. At the time, it was the first time the animal care staff had attempted breeding, so they were all very puzzled by the fact that only blue color jellyfish were being born.

This experience suggests that the color of jellyfish is likely determined by some trigger before they even become polyps. If eggs are collected from white or brown jellyfish, will the jellyfish born in the next generation also be the same color? Do males need to be the same color as females for their color to change? Or is there some other factor at play? The challenges for the animal care staff continue.

Please join us in watching as the aquarium is one day filled with colorful jellyfish.

Check out the Kyoto Jellyfish Research Club for other jellyfish columns!