find old arowana is required as part of the main story in The Legend of Zelda: Tears of the Kingdom.
You must offer one to Sidon’s betrothed, Lady Yona, in Zora’s Domain as part of the main quest “Sidon of the Zora”, to get the first piece of Zora Armor.
Ancient arowana locations in Zelda: Tears of the Kingdom
From the beginning of the game, we recommend two places to find ancient arowanas.
The easiest way is to go to the ponds on the Great Sky Island (where you started in the game). We found plenty in the small floating ponds north and east of the Nachoya Shrine.
Image: Jeffrey Parkin | Sources: Nintendo EDP/Nintendo via Polygon
You can also listen to Yona’s instructions, which is to search Dentothe blacksmith on the east side of Zora’s Domain, for a clue where to find one.
He points to you Mipha’s Court near the top of Ploymus Mountain. You can go to the Ihen-a-shrine to get close.
Image: Jeffrey Parkin | Sources: Nintendo EDP/Nintendo via Polygon
From there you climb the long staircase to the southwest. You will find at least one old arowana in the pool at the top.
Image: Nintendo EDP/Nintendo via Polygon
Wherever you collect the ancient arowana, return it to Yona in Misha’s Court, and she’ll give you the Zora Armor chest piece (which grants you the ability to swim up waterfalls) and allow you to continue with the Zora’s Domain story quest – which eventually ends at the Water Temple.