The Chub in Stardew Valley is one of the worst types of fish in the game. No one wants it as a gift, and it's only useful for the Field Research Bundle at the Community Center. After a certain point, they just take up space more than anything else, which means they can be very easy to find.
Where to find Chub in Stardew Valley
You can find chubs in Cindersap Forest River or Mountain Lake. This is one of the few fish you can catch at any time of year, which may be why they're so cheap. You can see where you should fish on the map below. We've marked it with blue and dark red circles.
If you don't want to shop for them, you can buy them from Krobus at his shop or the Traveling Cart. They cost 200g at Krobus' shop or 100 to 150g at the Traveling Cart. Additionally, you may find one in the trash, but this is mostly randomized, and if anyone catches you, they won't be happy. We recommend fishing for them since they're easy to catch, but also to move up to Sunfish or higher quality fish if you can.