The Himeji City Aquarium in Hyogo Prefecture, Japan, features a specially designed transparent water tank that allows visitors to clearly observe small fish swimming "upstream" against a rapid current. This innovative exhibit has recently gone viral on Japanese social media platforms, captivating nearly 10 million viewers and drawing widespread admiration for its ingenious design.
A Japanese user named "T-98" shared an 11-second video on the social media platform X (formerly Twitter) on the 16th, filmed during a visit to the aquarium. The explanatory sign in front of the tank explains that the water level in part of the tank drops every half hour, enabling visitors to see how the fish leap and swim upstream against a small waterfall to reach another water area. This dynamic display vividly recreates the natural behavior of fish navigating challenging river currents.
The video sparked enthusiastic comments such as "I could watch them jump all day," "The person who came up with this exhibit is a genius," and "The fish actually seem to fly! It's amazing and adorable!" Viewers also noted the educational and entertainment value of the exhibit, with some suggesting it could inspire further research into fish behavior.
The viral phenomenon extended beyond Japan, catching the attention of Taiwanese netizens after being shared by Li Renyi, an administrator of a popular Taiwanese Facebook group focused on Japanese marketing. While some discussions touched on environmental construction concerns, many users humorously referenced historical figures in playful comments about the upstream swimming fish.
In an interview with Japanese media, the Himeji City Aquarium explained that the "viral" tank is deliberately designed to simulate a wild river environment. When the water level rises, fish can freely swim anywhere in the tank. However, when the water level changes, the flow path is restricted, forcing the fish to exhibit their natural instinct by leaping upstream over steps in the current.
The tank houses fish species such as Ayu sweetfish and Zacco platypus (also known as Oikawa), which naturally display upstream swimming behavior in the wild. This authentic simulation offers both an educational experience and an engaging spectacle for visitors.
この展示いいね pic.twitter.com/XXNLUtYFCq
— T-98 （@T98ver2） May 16, 2025
