Overview

There are several possible groups to obtain fish from when you catch a fish

Name: General
Typically contains (with exceptions): Green grade fish / Plump Coelacanth / Glass Bottles

Name: High-Quality
Typically contains (with exceptions): Blue grade fish

Name: Rare
Typically contains (with exceptions): Yellow grade fish

Name: Prize
Typically contains (with exceptions): Red grade fish / Relic Shards / Troll 1% Mudskipper

Name: Trash
Typically contains (with exceptions): Silver & Gold Keys / Relics / Laila’s Petal

High-Quality

High-Quality fish are typically blue grade fish.

With the fishing size tournament, this fish group was renamed from “Big Fish” to avoid confusion. The group has no influence over the actual size of fish.

You can affect their rate with the following methods:

Item: Ash Tree Float (https://bdolytics.com/en/NA/db/item/16167)
Group Bonus: +11%

Item: Whaling Lightstone Set (https://bdolytics.com/en/NA/db/lightstoneset/161)
Group Bonus: +6%

Item: Calpheon Fishing Rod (https://bdolytics.com/en/NA/db/item/16164)
Group Bonus: +11%

Rare Fish

Rare fish are typically yellow grade fish.

You can affect their rate with the following methods:

Item: Maple Float (https://bdolytics.com/en/NA/db/item/16168)
Group Bonus: +5%

Item: Sharp-Eyed Seagull Lightstone Set (https://bdolytics.com/en/NA/db/lightstoneset/162)
Group Bonus: +5%

Item: Mediah Fishing Rod (https://bdolytics.com/en/NA/db/item/16164)
Group Bonus: +5%

Item: Palm Tree Float 🌴 (https://bdolytics.com/en/NA/db/item/16170)
Group Bonus: +5%

Item: [Event] Wise Housekeeper (https://bdolytics.com/en/NA/db/item/760966)
Group Bonus: +5%

Item: [Event] Crispy Goldfish Delight
Group Bonus: +5%

Prize Fish

Prize fish are typically red grade fish, but unfortunately often also Ancient Relic Shards.

Prize fish can only be obtained through Fishing Mastery.

How does the game determine which fish is caught?

Theory

Personally I believe there are essentially two rolls:

1. First it rolls for the fish group (% determined as seen in the image always normalized to 100% )
2. Then it rolls within that group for the actual fish itself

Diagram normalizing fish-group weights from 105% to 100%, resulting in a 4.76% Prize-group rate

I believe the game does NOT roll prize fish first, or use a “Roll-Down” Method from all we can tell.

Data

Empirical data for this was collected by

- shrddr (https://discord.com/channels/371035077037129729/371698180405985301/1229359808780566571) Sheet (https://docs.google.com/spreadsheets/d/14Q3nAzy-hYxVIkrEYoWe_wwO1pPMZ3gIVwa43_ONHJY/edit?usp=sharing)
- myself Sheet (https://docs.google.com/spreadsheets/d/1RXWi6l2-7I0AVz42udP_OzjTvGqHF-leODWfnN9Jkwk/edit?gid=147899036#gid=147899036)
- Mikatto (https://discord.com/channels/371035077037129729/371698180405985301/1229382865201004595) (confirming, not published)

For my own testing i used a consistent setup of 1600 mastery = 4% expected prize rate with +10% chance to catch rare fish. The actual observed prize rate was only 3.55% in 33.6k samples. At 99.9% confidence this means the actual rate lies in between +- 0.33% of the observed 3.55%. (So at best 3.88% which is below 4%).

Another ~9.4k samples were collected by shrddr with +11% High-Quality float at 1900 mastery which resulted in 4.07% vs. 4.75% expected.

Negative samples (no fish modifiers) were collected by shrddr which resulted in

- 4.55% vs. 4.75% expected at 1900 mastery (17576 samples)
- 4.72% vs. 4.625% expected at 1850 mastery (10901 samples)

Confirmation

According to one Korean player who presented this theory and asked for clarification, they received a response from Korean customer support confirming that increasing one group’s rate means decreasing the rate of another group.

Korean customer support response explaining that increasing one fish group probability lowers another group probability

Arguably the translation and or response aren’t 100% clear but it at the very least confirms that prize fish rate is impacted by increases in other group rates.