The unique way the eggs of Spotnape Cardinalfish are raised.

At Tokyo Sea Life Park, in the "Seaweed Forest" tank, you can observe the very unique and interesting behavior of a fish called Spotnape Cardinalfish. The black-spotted Spotnape Cardinalfish is a fish belonging to the Apogonidae family, measuring approximately 8 cm in length. Its body is reddish in color, and it is characterized by a pair of black spots on its head.

Now, if you observe the Spotnape Cardinalfish closely, you may notice some individuals with a swollen, protruding lower jaw. These are males in the process of "mouthbrooding." Mouthbrooding is the practice of protecting eggs from predators by placing them in the mouth and raising them until they hatch; it is also known as "mouthbrooding."

Spotnape Cardinalfish usually live in groups of several hundred, but during the warm breeding season, male and female pairs begin to form within the group. The female lays several thousand eggs in a cluster at once, and the male fertilizes the eggs with sperm. The male then immediately takes the eggs into his mouth and protects and nurtures them in his mouth for about 7 to 10 days until they hatch. During this time, the male does not eat.

They appear to be in pairs.

Mouthbrooding began to be observed in the tank from early June, but a little before that, from early May, the amount of food they were eating increased so much that the usual amount of food was nowhere near enough, and we had to increase the amount. Perhaps they were eating a lot of food to store up energy in preparation for breeding. As animal keeper, it was satisfying to watch them eat so enthusiastically.

As September began, more individuals started practicing mouthbrooding, and the amount of food they ate decreased dramatically, which made me feel a little sad.

Also, during this season, you can see them moving their mouths in and out, taking eggs in and out. This is how they deliver fresh seawater to the eggs and supply them with enough oxygen. They are definitely not eating the eggs!

It appears to be taking in seawater with its mouth open.

You can observe the unique and interesting behavior of Spotnape Cardinalfish up close, so be sure to pay attention to it!

[Tokyo Sea Life Park Animal Care and Exhibition Staff, Taisei Kobayashi]

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