Wisteria Jellyfish Yields & Variable DH/TH Yields in General

tl;dr: More gathering won't make you stop getting 8 Wisteria Jellyfish or 5 Gugrusaurus from TH.

Gathering's impact on Double Hook/Triple Hook is on yield, but it is on increases from 3 to 4 or 5 to 7 or 2-3 to 3-4 or 3-5 to 5-7, etc. Gathering has never been demonstrated to impact what you can get from variable yields, and most fish in the game don't even scale with gathering in the known way either.

Double Hook/Triple Hook are unique in that they function in an easily observable way (when they scale, which is almost never) and have been very consistent in how they work, demonstrated and observed for years. The scaling is very simple, because there are two possible increased yields that can be reached. This means when a fish with a non-variable yield scales it will give at least 2 with Double Hook, then at or a above a certain gathering give 3, and when at or above an even higher gathering give 4. The gathering required to reach the maximum yield can be simplified as: gathering required for 4 = (gathering required for 3)×1.5

There is no difference with Triple Hook, meaning a fish that has increased Double Hook yields of 3 and 4 will have increased Triple Hook yields of 5 and 7 that are acquired at the same gathering ratings as the Double Hook yields. Triple Hook gives you more but has the same functionality the same as Double Hook.
There is also no difference with variable yields, meaning a fish that has increased yields of 2-3 and 3-4 on Double Hook will scale in the same way and at the same gathering ratings as other fish of its iLvl that have fixed yields.

The only places in the game where this scaling can be observed are on fish from ARR, HW and the Diadem and the gathering required is based on the iLvl of the fish. Elsewhere, fish either have fixed yields that never change with stats or the abilities do nothing and always yield 1.

Significant work has been done and continues to be done to understand how these work, but the answer from this work is almost always very boring. However, even with this ability being one of the least opaque things about FSH a lot of misconceptions remain around it, specifically around variable yields.

You'll Keep That Yield

Variable yields are a type of yield. When scaling is a factor, they are specifically an increased yield. This means that when a fishes yields do scale with gathering a fish can lose its variable yield if your gathering decreases enough.

As an example, if you DH Ice Faerie at
- ≥456 gathering you will catch 3-4
- 304-455 gathering you will catch 2-3
- ≤303 gathering you will catch 2

This means that variable yields can be circumvented, to gain the minimum. They cannot be circumvented while maintaining the maximum yield.

When a fish yields 2/3 on Double Hook/Triple Hook, there will never be a gathering at which it will yield 1. Similarly, if a fishes increased maximum yields are 3-4/5-7 or any other variable yield, there is likely no gathering at which one of the variable yields is not attainable.
Using Ice Faerie as the example again: it has the lowest gathering breakpoints for a fish with a variable yield but still yields 3-4 at 5000 gathering.

Most of this is not particularly relevant to any player when using these abilities because, other than six fish from the Diadem, by the time you reach the level to be able to get Double Hook you should be in gear that already provides you the maximum yield. 897 is the highest gathering breakpoint for Double Hook/Triple Hook on fish from Heavensward, and afterwards they do not scale in the overworld anywhere.

On fish that do not scale, the variable yields still cannot be circumvented. If a fish has a fixed yield of 3-4 that is its yield, forever, as far as we can tell.

Can You Change the Odds?

That increased or fixed variable yields cannot be lost is easily observed. Push Double Hook and Triple Hook a few times on something with variable yields at high gathering and you will see this.

A question that has existed since Double Hook was implemented has been can you make it more likely that you will get the higher yield?
The answer to this also appears to be "No."

An example with Sky Faerie. 542 gathering is the DH3-4 breakpoint for Sky Faerie.

On this fish Double Hook, with 2 yields, is a simple 50:50, while Triple Hook, with 3 yields, provides a different but seemingly consistent ratio.

The most interesting thing about variable yields is that, based on work done, there is some suggestion that the ratio when there is 3 yields is potentially not fixed to the above ratio, but better datasets need to be collected on this. This means that current data suggests that on some fish with variable yields you may be more likely to get the maximum (or minimum), but if that is the case it is because that is a fixture of the fishes variable yields, not related to gathering.
Collecting data on this hasn't been urgent (sitting on multiple small data for 4+ years) given where these yields have been (most relevant is for intuitions where TH always provides the minimum needed to trigger) and the tedium given its required using Triple Hook.

Wisteria Jellyfish

Cosmic Exploration has finally provided a contemporary fish with a variable yield where gathering matters for it at all.

Outside of Heavensward and Gigant Clam, the other variable yields we have had accessible are in Ocean Fishing on fish where stats don't practically matter. The impact of gathering on the variable yields has still been passively tested on these—since yield directly impacts points which impacts score—and it still appears that variable yields have fixed ratios.

Since Wisteria Jellyfish is the first fish implemented since Double Hook was implemented that has a variable yield and an observable relationship with gathering (the typical soft breakpoint to provide the lowest escape rate observed on most white rarity fish/other fish in Cosmic Exploration) it is a great curiosity. It is also unique in that it is the only fish with a variable yield that has three yields available on Double Hook.
It also, conveniently, is by far the easiest fish to test on thanks to GP resetting if you finish a mission and its mission being extremely quick to complete.

From these datasets a gathering differential of 1000 does not appear to provide a meaningful adjustment to acquired yield. We also observe a different ratio than observed from the 3 yields for Sky Faerie, not unexpected as explained previously, and it appears the maximum yield is the least common one.

A problem, while Wisteria Jellyfish is contemporary, is that testing a wide range of gathering is difficult because, due to Cosmic Exploration fish having the typical soft gathering breakpoint behaviour, it and Riotus Dianthus quickly gain very high escape rate rates. At 4000 the escape rate was high enough to significantly slow down testing since the easiest way to do the mission quickly is with the limited bait, which you lose (in addition to the GP) when it escapes, requiring waiting on GP regen.

This will be revisited in Evercold instead of suffering through 3000 gathering while we have no evidence to support the behaviour we are searching for existing anywhere else.

Is it reasonable to expect it to be possible for Double Hook/Triple Hook to yield only 7/10 in the future? In my opinion, no.

Cosmic Exploration provides different yields not observed anywhere else but all other observable behaviour Sinus Ardorum - Oizys and on every other fish in Auxesia has been consistent with previously observed Double Hook/Triple Hook behaviour. Ocean Fishing did exactly this too.
Diadem used the scaling Double Hook/Triple Hook have in in something contemporary for the first time ever, and while it took until an expansion later for the highest tier of scaling to be achievable, that the scaling existed was still apparent during Shadowbringers. I think if there was some kind of scaling, novel or not, in Cosmic Exploration it would be observable already.
Cosmic Exploration yields as we understand them are not impacted by gathering, like Ocean Fishing's, and I do not consider it reasonable to expect there to be a new heretofore unseen type of gathering scaling added. This lack of impact with gathering generally has been reasonably proven on every planet. Low-EW level gathering provides the same yields as 5000 gathering on every planet on Lv. 100 mission fish. As with the above, despite my skepticism, this will be revisited in Evercold because it is both easier and more practical to go significantly higher than lower from the soft breakpoints.

Confidence

The language used here is uncharacteristically confident. This is partially due to the length of this text and it being easier to write what is going to follow from this point than to qualify something every other sentence. It is also due to the amount of time I have spent looking into Double Hook and its functionality, or lack thereof.

Is it possible Wisteria Jellyfish does something new with its variable yields? Yes.
Is it possible for fish with variable yields to gain scaling with gathering or perception or a secret third thing that makes you more likely to get the maximum yield? Yes.
There is almost no 'rule' FSH has that does not have some sort of exception and it is, in my opinion, extremely stupid for someone who claims to be knowledgeable about FSH to say anything definitively about almost anything.

While I think all of the conclusions presented here are extremely reasonable, I still test every fishes yields at the start and end of the expansion for a reason. I've continued to test Sky Faerie's variable yields periodically for the same reason. Although I think that Double Hook/Triple Hook's unique consistency for something FSH has is important to consider, there still do exist some exceptions in places with some of its functions; how variable yields work is just not one of those, but it doesn't mean they can't make an exception for those too.

As previously stated, Cosmic Exploration provides new yields and so did Ocean Fishing. When yields scale with gathering, it is by iLvl and it is almost entirely increasing by iLvl but, for some reason fish that are iLvl 23 have lower breakpoints than fish that are iLvl 21 and 22. That some (most) fish just don't scale at all can be considered an exception, especially since they have shown they can just assign a yield to be, probably, whatever they want it to be.

I just think that since all of the [meaningful] exceptions have been new yields and ignoring that the ability interacts with gathering at all, new yields and ignoring scaling are the most reasonable exceptions to expect.

I am of the opinion that most breakpoints are assigned manually (the exception being the increased yield DH/TH have that has observable scaling) and that at least some things about FSH are basically arbitrary. The people responsible for designing FSH can do whatever they want—and it seems to me, at least, they do—and if it is technically possible for them to make variable yields able to be adjusted by something, I would never be confident saying it will never be done.