The Legend of Zelda: Tears of the Kingdom is filled with side quests that Link can take on to assist the people of Hyrule. Between monster hunting and tracking down the lost Princess Zelda, players can also take on some less critical issues. Helping out one of the Zora who has a taste for 
Bright-Eyed Crab is one such side quest.
Players can find Zora's Domain in the east section of Hyrule in The Legend of Zelda: Tears of the Kingdom, and it is initially suffering from a deluge of sludge falling from the sky. After this has been resolved, players can stick around and help out the Zora as they recover from the crisis in a bunch of smaller ways.
A Crabulous Deal
To start this quest, head to the Zora General Store as shown in the image above and speak to the proprietor. Cleff discovered a love for Bright-Eyed Crab after finding and eating one during the crisis, and now he desperately wants to acquire some more. If Link brings him 10 Bright-Eyed Crabs, he'll offer a reward, so it's time to get hunting.
Luckily, Bright-Eyed Crabs can be found all over Zora's Domain, and players won't need to travel far to track some down. They can be found on the rocks at the feet of the pillars holding up Zora's Domain, and atop various towers nearby as well. They can also be found scuttering about in the pool of water at the center of the Domain on the lower level.
Once a Bright-Eyed Crab has been found, players should take a photo of it and use the Purah Pad's Sensor+ to detect extra crabs. With help from Sensor+, Link shouldn't have any trouble tracking down nine more crabs without needing to leave Zora's Domain. Players should note that, according to their description, Bright-Eyed Crabs are more common in rainy weather. There's a ton of them around the Domain anyway though, so the weather is unlikely to be a huge issue.
After acquiring 10 crabs, players can head back to Cleff to hand them in and receive a 
Sapphire as a reward. This completes the quest, though players can always come to Cleff with any Bright-Eyed Crabs they find to trade for more rewards and likely turn a decent profit in the process.
The Legend of Zelda: Tears of the Kingdom is available for Nintendo Switch.