How to successfully fish

You should look for a stone on the ground to sharpen your knife. There is no type of interaction or specific button to press. Just "stabbing" the stone is enough. You'll know it's working if there are sparks.

If you are playing as Chris your knife will be a "Recurve" blade. Its wire is more precise in cuts. Sheva's one is a Clip Point.

Chris' Knife:
The recurve blade was initially developed to cut fish, but is widely used in the most diverse gastronomic areas. It is a very long and sharp tool, initially used as a melee weapon. It usually has a stainless steel blade with a smooth edge and a wooden handle fixed with aluminum rivets.

Sheva's Knife:
There is a cut or clip on its dorso that may have a false edge, complementing the cut. This false edge can be sharpened to further increase piercing capacity. It is used in the famous Bowie Knife, in Survival knives and some Tactical Knives.

The best lake I found was the one in Chapter 3, Subchapter 1, in the Marshlands Checkpoint. You can find a map of the area in the central-west dock. Use the airboat to get there.

You will need to clear the area as it will be infested with crocodiles. After that, stop and watch to see if any fish are jumping. You can see waves of water forming in the direction the fish swim. The fish might only appear after you get the Raptor Slate key item.

This step may seem a little difficult, but I guarantee the fish's hitbox is large. I recommend a maxed-up S75 Sniper Rifle to kill them, it's a weapon with a very high precision.

*The S75 Sniper Rifle can be picked up for free in Chapter 2 Subchapter 1,
or purchased for a small price of 2,000₦.

Go to the fish, (just walk, so as not to scare away the other fish nearby) when you get to it, take the money, (you can earn from 100₦ to 200₦) and press F to clean it. Cleaning it means removing the fish's organs and also its scales.

In this very same chapter you will find some hang lines where you can hang the fish. Approach them and press F. At this point Chris will use the "Charque" technique and hang the fish he caught. At the end of the chapter they will be moved to the Item Box and you can sell them for 1,200₦.

It was not so hard, huh?

This can be a good income to help you buy items and upgrade weapons, as well as being fun after you've already beaten the game several times on the most varied difficulties.

Very Special Thanks to Gabafonso - Helped me a lot to get the screenshots.