Along with the Brick rod, the developers of Fisch have also added a new mutation to the game called Studded. Unlike other mutations, this is an extremely valuable mutation that can literally allow you to make money out of thin air if appropriately used. So, here is a detailed explanation of the Studded Mutation and how to unlock it.
Basically, anything you catch with the Brick Rod will provide you with the Studded Mutation that increases its value by twice. Yes, that's the feature of the Studded Mutation, which allows you to make money much more quickly, as you can sell even the simplest of fish for twice its value. Speaking about the appearance, all of the fish with the Studded Mutation will look like they are made out of brick and resemble a LEGO piece. To conclude, you need the Brick Rod in Fisch to get the Studded Mutation.
Acquiring the Brick Rod is a lengthy process in Fisch, but let me briefly explain it to you.
For more on Fisch, How to get all items in Roblox Fisch (Locations) or All 5 Secret Fishes in Fisch (Atlantis Update) – Roblox