First of all, english is not my native language. I know english but not an expert, so I will use the help of an online translator. I decided to translate my original spanish guide because there are very few tutorials for this game. If you can't understand something, just let me know.

It's not as simple as it sounds, it's not just a matter of use the biggest thing we have.
The rod, reel, line and leader all have a stipulated maximum weight resistance. Can we lift fish heavier than the weight of the equipment? Yes, to a certain extent, but we can't expect to lift 60kg with an 18kg rig.

To maximize effectiveness and avoid to break anything, there is an ideal way to set it up.
In "theory" it is done in the following way:
Taking into account a weight from heaviest to lightest, we should set up the rig as the following example:
Rod: 7.5kg
Reel: 7kg
Line: 7kg
Leader: 6.4kg


Let's look at it as links, the first link that will break in case of an extremely strong pull, will be the weakest one. If the build is done as in the example given, the 6.4kg leader would break. In an ideal scenario, always but always the leader should be the weakest link in the rig, it is not the same to replace a hook and bait/lure, as it is to repair a broken rod or reel.
Does this mean that any big fish that bites will break the leader? Absolutely not. We could set a hook 5 and let a shark bite it, and if everything is set up right will just take the line all the way to the end and let loose. This is where one of the most important things comes into play, the reel brake.

In Fisher Online, unlike other fishing games such as Fishing Planet, all the reels have 20 braking points (friction), which we control with the mouse wheel. To brake effectively and especially safely, we will have to use mathematics.

When we start the game and are inexperienced, we adjust the brake randomly, taking a look at the bar and see the red does not reach the top. But there is a calculation that allows us to know how much brake we can apply without breaking something, in the worst case scenario, the fish will end up taking the whole line and escaping, but nothing will break and we will not lose hooks or bait.

So, do we put the brake directly on 19? Nooo, everything will depend on how the equipment and its components are assembled.

In the example given above, the reel is 7kg. If we divide those 7kg in 20 braking points that the reel has, it gives us a result of 0.35kg per point.
7/20= 0.35

Now we have how much brake applies per point, let's get to the interesting part. What is the weakest link in the rig? The 6.4kg leader.

In this example, if we want to brake safely, the maximum brake to use would be 18. Since 0.35kg of each braking point, multiplied by 18 gives us a total braking of 6.3kg. If we were to set the brake at 19, we would be using the brake at 6.65kg, greater than the resistance of the leader, which would cause the leader to break.

18x0.35= 6.3

With heavy fish, we will see the red bar at its maximum, but rest assured that if the brake is less than the weakest link of the rig, nothing will break.

To clear things up:
7kg (reel) / 20 braking points = 0.35kg
6.4kg (weakest link, leader) / 0.35kg = 18.29

VARIATIONS:
You can always have a rig of different weight strengths, for example, 12kg feeder rod, 35kg reel, 15kg line and 11.4kg leader. The example given at the beginning is an "ideal" case, the important thing is that ALWAYS the leader has to be the weakest link, and that the maximum brake applied is less than the leader.

In this last example, a 35kg reel, with a leader of 11.4kg.
35 (reel) /20 (braking points)= 1.75
11.4 (leader) / 1.75= 6.51


The maximum brake we could apply is 6, which is equivalent to 10.5kg.

Remember, the leader should always be the weakest link, and the braking point should apply less friction than the leader. Good fishing for everybody.