Freshwater goby

The Freshwater Goby (ドンコ, Donko) is a rare fish that can be caught in the river in every game. It has a small shadow, and it appears all year round. It can be caught between 4 PM and 9 AM.

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After donation, the freshwater goby can be found in the middle-left tank.

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An information board in the aquarium will display this description of the freshwater goby after donation:

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Once donated to the museum, the Freshwater Goby can be found in the second level of the waterfall tank with the Yellow Perch and Pale Chub.

Real-world information
The freshwater goby is typically a native fish to tropical and temperate areas of Asia. There are numerous types of these so-called fish, known as haaze in Japan. All live in freshwater rivers where they scavenge the riverbed for prey.