The tuna money-making method in "Fishing Force" is a very effective way to earn cash. To use it, go to the shop first, store all your items there, then buy frisbees to fill your backpack. Next, head to the weapon shop and drop all the frisbees on the ground.
How to Make Money with Tuna in Fishing Force
Gambling is the fastest way to make money in this game. Sell the first few tuna normally, and once you have some margin for error, keep betting on green. You'll succeed eventually, and just one win will set you up for life. Consider previous losses as savings.