Experience the mysterious world of fish through the sight of robust young fish
Karibu Suzuki, a wharf fish collector and museum director, spent his childhood observing fry and juvenile fish on the quays of fishing ports and was fascinated by their "robust way of life." Wanting to share the charm he felt with many people, he opened an aquarium specializing in juvenile fish, a rare sight in the world, in 2022 under the slogan "Happy Fish!"
The fish, swimming vigorously in their tanks with their tiny bodies, are so cute that you just want to cheer them on. And yet, this world is profound. It's not just that they're different in size compared to adults; their appearance also reveals the mysterious ecology of juvenile fish. For example, they may hide from predators by camouflaging themselves with dead leaves or pumice floating on the ocean's surface, or they may change their patterns to avoid getting caught up in territorial disputes between adult fish. These are all examples of the various ingenious ways they have devised over the course of evolution to survive with their small bodies. The aquarium is filled with unusual and mysterious tanks not found in other aquariums, such as a comparative display of adult and juvenile fish of the same fish, and a live display of deep-sea juveniles that spend their early childhood in shallow waters. You can also see how the same fish changes after they are born.
A juvenile red lionfish has a charming feature: its whiskers. What looks like an open fan are its pectoral fins, which are useful for surprising predators and cornering prey. Its dorsal fin is poisonous. 
This is a sea urchin...or rather, an owl crab that has been infested by sea urchins. Because it barely moves, coral and other organisms grow densely all over its body, which is heartbreaking. 
An adult starfish. The star-shaped vertebrate that is present in juveniles disappears as they grow, and they become more like a bun. 
The monstrous mantis shrimp is a ferocious creature that may be small but can deliver a powerful punch, shattering the shells of crabs and seashells with a single blow.
"Here, we treat the fish as individuals, not as species, and we raise each one with love. Every March, we hold a graduation ceremony to send off the adult fish so they can begin their second life at another aquarium, and sometimes the attendees are moved to tears by the memories they have of the fish."
"We're very grateful for the support," said Ishigaki Koji, public relations officer. The aquarium is limited in size, at just 265 square meters, so communication with visitors is also a major priority. The explanatory panels, hand-drawn by Director Karibu Suzuki, feature illustrations such as "a rhythmic gymnastics ribbon that comes to life" for the ribbon-bearded moray eel and "a boxer that can kill in an instant" for the peacock mantis shrimp. Another feature of the aquarium is that it allows visitors to learn about the complex ecology of the animals in a fun way, with occasional humor thrown in.
"Young fish have more ingenuity in how they protect themselves. That's what's fascinating about them, but the opposite is true for the pufferfish, which develops spikes on its front and back horns as adults to protect itself from being eaten. There are many creatures that defy the evolutionary process. That's what makes them so fascinating."
Even though fish may look similar at first glance, there are as many different and unusual characteristics as there are species, and each has its own unique personality. What the young fish provide us with is a vibrant and robust world full of diversity.
Happy fish. Small and mysterious young fish
Young kongo pufferfish 
Congo pufferfish
Juvenile fish are round and balloon-like, but as they grow, their face takes on an irregular, rectangular shape. When they reach adulthood, they develop impressive horn-like spines for self-defense.
Juvenile Sakuradai 
Sakuradai
All juveniles are female, but as they grow they change sex and become male. Their body color also changes from orange to a beautiful red, as their name "Sakura" suggests.
Juvenile Ishigaki pufferfish 
Ishigaki pufferfish
A member of the porcupinefish family, it is characterized by its large, round eyes. It loses the spikes and polka dots that it had in its juvenile form, and its spines (hooks) no longer stand up.
Juvenile Emperor Angelfish 
Vertical striped angelfish
As they grow, the spiral pattern changes to stripes, and their color also changes to bright blue and yellow stripes. The reason for the different pattern is to prevent them from getting caught up in fights between adult fish.
