What's the exact file I'm looking for?
I assume you have a copy of RPG Maker MV and know how to extract the game using enigmaVBunpacker from lifeinhex.com, the latest version of which can be found on this blog entry as of the time of this post:
You must be registered to see the links
.
Once you open up the game and go to the beach map, there are 3 tiles that roll the dice for fish spawn, found at 24,5; 24,8; and 24,11. The first tab on each tile sets the FishRandomizer roll, the SizeRandomizer roll, the actual Fish roll (Fish1,2, and 3 for each tile) and then appends value to the Fish roll based on if you have the Crafted Clover. Then each subsequent tab has the fish you can roll depending on the value of the Fish roll achieved, and then assigns a weight based on a random range depending on the species and size of fish you rolled based on all the previous variables.
So the first roll that takes place is the FishRandomizer roll, which can roll from 0-100 up to 3 times depending on whether you have Find Rare Fish and Bought Bigger Fish book. Now those are actually misleading, because you would think it rolls 3 times and would keep the biggest roll, but in fact it does not. It merely rolls 3 times in an attempt to hit 100, so your odds of hitting 100 go from 1/101 to 3/101, and only stops rolling if it hits 100. So what I do is set the subsequent roll ranges to higher values like 50-100 and 70-100. That way even if you don't hit 100 you are actually rewarded for having the higher number of rolls even if it still doesn't store the highest roll and keep that one.
Once the FishRandomizer roll is chosen, it assigns a range of possible Fish variable values in nested increments. So if you hit 100, you can roll a fish size variable value of 16-18 based on a combination of the SizeRandomizer variable roll which is 0-10 by default and 5-10 with Bigger Fish, and then a 1 in 4 chance to increase the value to the max for the range if you don't hit 10 with the Crafted Clover. Each reducing increment of FishRandomizer lowers the maximum Fish variable value you can roll, limiting the size of fish you can roll based on that value. So 16-18 for 100, 13-15 for >=97, etc. I usually increase the Clover roll to a 1/2 chance and the Bigger Book range to 7-10.
Now once you've set the first tab variable to what you like, then you can set the tries, odds, and weight range for each individual fish. Smaller fish have 4 tries to be reeled in and larger fish have 1, with other fish being between those ranges. Odds determine the chance of you hitting a particular fish on hitting a Fish variable value. For example, let's say you hit Fish1 = 18 based on the initial rolls, which is roll you need to catch the largest Great White Shark and can only be achieved with a FishRandomizer roll of 100, and then a SizeRandomizer roll of 10 or a 1/4 Clover roll after not hitting the SizeRandomizer roll. Your chances of hitting the largest Great White Shark is still extremely low, because its fish odds value is 10, up againt a total of about 700-1000 between all other fish that can roll on the Fish1 tile (can't be assed to do the math, just a guesstimate) so somewhere in the neighborhood of 1%. Then once you do hit that roll, its weight ranges from 2000-3100, so your odds of hitting the highest end of the weight range are even lower. So you're talking about a less than 1/1000 chance of seeing a Great White that weights over 3000 lbs, and then 1 roll at capturing the fish once you see it.
I would adjust the fish odds of all the fish to meet whatever ranges I wanted to see based on the stage of the fish quest I was on, and then adjust the number of tries at catching it and the weight range so I can experience the "challenge" without just copping out and editing my save. Just reduce the randomness and still get to experience the gameplay as it was meant to be.