This is now fixed :)
You need to catch a Goldfish (as seen in the achievement picture)
*Goldfish is the type of fish not just a gold star fish*
The Goldfish can be caught in the far right fishing spot by the lighthouse (the sea) Use the excellent rod and lure with gem and aim for the last area that says 2% (it will be 5% at night). Keep fishing until you catch the Goldfish.
To get the excellent rod and lure with gem:
You need to do tasks for the fish guy at the lighthouse until the point you can sell fish to him. After, sell him fish until you unlock his tier 3 items to buy. In his tier 3 items is the excellent rod and lure with gem.