Pale chub

The Pale Chub (オイカワ, Oikawa) is a common fish found in rivers. It can be found in all of the games in rivers between 9 AM – 4 PM all-year round. It is an inexpensive fish that sells for 200 Bells at Nook's Cranny.

Donating to the museum
When handing the Pale Chub Blathers in the museum, he will say the following before thanking the player for the donation:

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Upon donation to the museum, the information board in front of the tank says:

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Once donated to the museum, the Pale Chub can be found in the second layer of the waterfall tank with the Tilapia and Dace.

Real-world information
Zacco platypus, also known as the pale chub is a type of freshwater minnow. It is listed as harmless and not in any danger. It can be found in Korea, China, and northern Vietnam. In Japan, the pale chub is also called Oikawa. It lives in fast-flowing rivers and streams, and it feeds off of insect larvae and algae, and smaller fish. During mating season, the male Pirani changes color rapidly to impress a suitable female. They actively feed during the evening or when the weather is overcast.