How the catch is decided
Every fish carries a set of conditions: which seasons it appears in, which water it lives in, and what weather it needs. Cast where the conditions match and it becomes a possible catch. There is one condition the game notably does not use — no fish in Fields of Mistria is restricted to a time of day, so 3am and midday offer exactly the same list.
What happens next is a draw in two stages. The spot first decides a shadow size — small, medium, large or giant — and only then picks a catch from the fish that can appear at that shadow. Nothing outside the drawn shadow competes. So a giant fish is not competing against a river full of minnows; it is competing against the other giants, and there are usually very few.
Inside a shadow the draw is weighted. Each rarity tier is worth a fixed number of "votes" — 300 for the most common down to 40 for rare — and a fish's chance is its votes over the votes of everything else in that shadow. Junk and treasure boxes sit in the same draw, which is why roughly one bite in six is not a fish at all. The counter-intuitive part: a fish gets rarer as more fish unlock in its shadow, even though nothing about the fish itself changed.
Weather and legendary fish
Weather comes in four kinds: clear, rain or snow, storm or blizzard, and windy. Windy days only occur in spring and autumn — 4 to 6 of them per season — and never in summer or winter, so anything needing wind has a narrow yearly window.
The legendary fish each need a specific weather event in a specific season and water — and, before any of that, the Legendary fishing perk. Without the perk they never appear at all, which is why they are listed on their own here rather than folded into the odds. There is no way to force the weather, so the practical approach is to take the perk early, keep the right rod and bait ready, and go the moment the forecast turns.
Using the planner
The planner answers in one of two ways, and the difference matters. Leave the place set to Anywhere and it groups the catch by shadow and gives a share within that shadow — read it as "when a shadow this size appears, how often is it this fish". It says nothing about how often each shadow appears, because that belongs to the individual fishing spot.
Name the place you are standing and it can say more. Each spot carries its own weighting for the shadows, so once the planner knows where you are it multiplies the two stages together and gives a real chance of pulling that fish out of that water. Where a location holds several spots — the Beach has thirteen — you get a range instead of a single figure.
That range is not an error bar. Both ends are the actual figure at an actual spot, and where you stand decides which one you get. A low end of 0% is the most useful thing it can tell you: at least one spot in that water never produces that fish at all. Four of Mistria's eight river spots put no weight on giant shadows, which is why Paddlefish there reads 0%–2.7%.
So use Anywhere to learn which shadow a fish lives in and decide what to cast for, and pick a place once you know where you are fishing and want the real odds — or want to find out whether the spot you have been standing at can produce your target at all.
Mine water is a separate system. Each layer of the mines has its own fixed list of fish with its own weights, and season, weather and the shape of the pool make no difference underground, so the planner drops those controls when you pick mine water.
Catching any fish costs 12 stamina regardless of size, so plan around food if you intend a long session. Fish are also museum donations and gifts — check the museum sets before you sell a first catch, and the gift finder before you sell a rare one.
Where the fish actually are
Only some water is stocked. Thirty-four fishing spots are placed across the eight outdoor areas, and eleven more boxes exist that seed nothing at all — water you can stand beside and never get a bite in. The Beach has by far the most at thirteen, then town with nine and the Eastern Road with five.
Two of them are on your own farm, in the river, and one more is the ocean at Sweetwater Farm. Neither is signposted, and plenty of players never try a cast at home.
Every spot weights the shadow sizes itself, and giant is the rarest everywhere it is possible at all — typically one vote against ten or more for the others. There is no spot where giants are common, so the way to catch one is repetition, not location.
One more thing that explains a frustrating morning: if the spot rolls a shadow and nothing legal fits it — the season is wrong for every fish of that size — the spawn simply fails. That share is not handed to another size, so an out-of-season spot does not fish slower, it sits there half dead.
