At the last part of the game, there will be a giant Mullet. Use a yellow fish or a grey fish as bait for the Mullet to eat it. Then you will earn 100 coins for a reward of catching it.

And one more:

If you buy a Flashing Lure Fishing Rod from the Sport Shop's catalog Snow and Sport and then play Ice Fishing, you will see that you are catching grey fish in addition to yellow fish. Each grey fish will get you double the amount of coins than yellow fish will.


Cool?

very (cool)