How to play

Your first spring

1. Open the breeding pond. Your two founders, a female and a male Kohaku, are already set as dam and sire.
2. Keep their feeder full. Spring warmth and food bring them into spawning condition. Both need condition 80, which takes about ten days.
3. Put in spawning brushes. They spawn overnight and the brushes are covered in eggs. The eggs hatch three days later.
4. Move the fry to the mud pond. It holds 10 fry to begin with, and you always get a full pond. Keep its feeder topped up: fry only grow while there’s food.
5. Let the season run. The clock stops at every netting day and at the end of each season, so you can step away and come back.

A game day is 16 seconds at normal speed, so a season of 30 days takes about eight minutes. Use the 2× and 4× buttons to speed up, or pause whenever you like. The ⏭ button skips to the next season (see below).

You won’t miss a spawn by accident

• Spring day 23: if there’s still no female and male in the breeding pond, the clock stops and asks you to choose a pair. Any fish of 29 cm or more can be chosen, and they swap places with whoever is in the breeding pond.
• Spring day 24 is the last spawning day. If a pair is in the breeding pond and hasn’t spawned, they’re set on the brushes automatically, whatever their condition.
• If you have no fish big enough, you can choose to skip spawning for the year.

Skipping to the next season

The ⏭ button next to the speeds races through the rest of the season (about three seconds). The days still happen: fish eat, grow and foul the water, and events still turn up. Before it starts, it warns you about any feeder that will run dry. It pauses for netting days, the spawn deadline and any fish that dies, then carries on afterwards and lands you on day 1 of the next season.

The farming year

Each year has four seasons of 30 days. Tap the date at the top of the game to open the calendar.

Ponds

• Breeding pond. Only your breeders live here. It starts with room for 2 and upgrades to 4 and then 6. A koi can join it at 29 cm and can spawn at 35 cm. If a pond is full or a fish is too small, the Move to list says why.
• Mud pond (grow-out). Fry grow on here from spring to the autumn harvest. It starts at 10 fry and upgrades in steps of five to 40 (¥90 to ¥1,500 per step). Bigger broods mean more chances of a great fish.
• Show ponds. Where your kept koi live and grow on, year after year. Name them as you like, for example “Tancho pond”. Each starts with room for 4 and upgrades up to 15. You can build one more show pond for every variety you’ve researched; each new pond costs more than the last, starting at ¥300.
• Each pond has its own care and upgrades. Filtration (three levels), an aerator, a net cover, water lilies, iris and lotus. Choose the pond in the tabs over the water, then use the Care and Upgrades tabs.

Water, food and health

• Water quality falls with stocking, fouling food and warm weather. Filters, plants and water changes bring it back up. Poor water slows growth, dulls colour and makes fish sick.
• Oxygen drops on hot nights and in crowded ponds. An aerator keeps it up, and a water change gives a quick boost because fresh water carries more oxygen.
• The feeder lasts roughly 12 days in summer and much longer in winter. If it runs dry, fish stop growing. After three hungry days they weaken, and only after that can they die.
• Food has properties: growth, health, colour, how much it fouls the water, and cold-weather value. Basic pellets are cheap and dirty. Wheatgerm (farm level 2) is gentle in the cold. Growth food (level 3) grows fish faster. Colour food (level 4) deepens hi over a season.
• Rearing. Every fish slowly takes on how well it’s kept. Good water and good food let its genes show fully; neglect makes it look and judge up to 20% worse.
• Sickness (fin rot, flukes, white spot, ulcers) comes with poor conditions. A salt treatment helps sick fish recover. Sick fish sell for less.
• Dead fish. When a koi dies of sickness or hunger in a show pond or the breeding pond, its pale body stays in the water and fouls it every day until you remove it. Tap the body in the pond, or press Remove in the side panel. Fry that die in the mud pond turn up in the net on the next netting day, where one tap disposes of them all. Fish taken by a heron or eaten by a sibling are simply gone.
• Herons take small fish unless the pond has a net cover; lilies give some shelter.
• Events are gentle and rare, about one per pond per season: spring rain, algae blooms, hot nights, falling leaves, dragonflies, a thin skin of ice.

Growth, tobi and runts

Koi grow when the water is warm and the feeder has food. Below about 10°C they barely grow at all, so winter is a rest. The side panel tells you how fast a koi is growing right now and why.

• Two genes decide growth. Size potential sets how big a koi can get (about 60 cm for an average fish, up to 88 cm). Growth rate sets how fast it gets there, from ×0.4 to ×1.6. Both are inherited, so a line of fast growers stays fast.
• In the mud pond every fry grows at its own rate, and bigger fry win more of the food, so the gap widens through the summer.
• A tobi (“jumper”) is a fry far bigger than its siblings. It’s a fast grower, and it eats small fry, especially when food is short or the pond is crowded. You might keep it to breed fast growers, net it out to protect the rest, or cull it if its pattern is poor. Real breeders face the same choice.
• A runt is well behind its siblings. Slow growers usually stay small; at each netting a button culls all the runts in one go.
• The grading sieve (mud pond upgrade, ¥160) sorts fry by size between nettings: it shows tobi and runts at any time and lets you net a tobi out to a show pond before it does any damage.
• Size tags (tobi, big for its age, runt) are plain observation, so you see them from the first selection. The growth gene itself shows at mastery Lv 4.

Netting days

Instead of inspecting fry one by one, you net the whole mud pond three times a year and sort it on cards. Swipe right or press → to keep, swipe left or press ← to cull. At the harvest, press ↓ to sell.

• First selection (summer day 6). Colour is only just showing. Cull the bent, the weak and the off-colour (Shiro Muji, Aka Muji and unnamed mixes). New varieties are discovered here.
• Second selection (summer day 26). The pattern is set and Gin Rin shows. With mastery level 2 you get a score estimate.
• Harvest (autumn day 15). Every fry is now a tosai. Pick a destination pond for keepers, or sell. Most tosai are worth ¥1–5; a good one is worth around ¥10. The real value comes from growing them on.
• Size tags on every card show tobi, fry that are big for their age, and runts.
• Dead fry found in the net are shown first, with one button to dispose of them all.
• Bulk buttons cull every sick, deformed or off-type fish in one go, or keep or sell all the rest. The apprentice upgrade flags the obvious culls for you.

Mastery and research

Each variety has its own mastery level. You earn it by raising, harvesting, keeping and selling that variety, plus a little each year for every fish of it you own.

Your farm level rises with everything you do and unlocks better food. Research costs ¥30 plus a little more for rarer varieties.

Dealers and the winter market

• Variety dealers open when you research a variety. They sell young tosai of that variety, mostly pond grade; Kohaku tosai cost about ¥27. Selling pays 70% of a fish’s value at mastery 0, rising 6% per level.
• The winter market sells one bagged mystery tosai each winter for ¥30. Common varieties are most likely, but anything can turn up. It’s your first way out of a Kohaku-only farm.
• Dealer koi can carry hidden alleles. About one in seven carries a hidden allele, which can surprise you a generation later. About 6% carry Gin Rin.

The progress track

A rough guide to how a farm develops. It’s meant to be slow.

1. Year 1The first spawn

   Spawn your founders, learn the three netting days, keep a couple of the best tosai and sell the rest for a few yen. Keep feeders full; that’s most of your spending.

2. Years 2–3Growing on

   Your first tosai become nisai, then sansai. An average nisai reaches 35 cm by its second autumn, so it can spawn the spring after. Fast growers get there sooner. Spend on a filter and a bigger mud pond. Kohaku mastery reaches level 2, and estimates start to appear at netting.

3. Years 2–4The first new variety

   Buy a mystery tosai each winter. When something new turns up, research it to unlock its dealer and a second show pond. Crossing it with Kohaku is where new varieties begin.

4. Years 4–10Crossing and lines

   Use the breeding calculator to plan crosses. Many varieties appear in the first cross; others only when you breed those offspring together. Build show ponds for your favourite lines and follow them in the family tree.

5. Years 10–25Chasing perfection

   Keep the best female and male of every spawn, run the biggest mud pond, and raise everything in clean water on colour food. Scores climb slowly into Show and Champion grades. The last few points take patience and luck.

6. Any yearThe rare rolls

   Tancho shows on 0.3% of red-and-white fry (more from Tancho parents). The Golden Seal is one in two thousand. Either can turn up in any spawn.

Tips

• Cull deformed and off-type fry at the first selection: every mouth costs food, and crowding slows the rest.
• Keep a pure Kohaku line going. It’s the base for most crosses, and hard to get back once mixed.
• Two koi that look identical can carry different hidden alleles. If a pair throws a surprise, both parents carry it.
• A net cover is the cheapest upgrade that saves fish. An aerator pays for itself in the first hot summer.
• Growth slows a lot as koi near full size. Big, high-grade adults are where the money is.
• Keep a breeder in reserve. If one of your pair dies, a young fish takes a year or two to reach breeding size.
• Fill the feeders before you skip a season. A dry feeder halfway through a skip means hungry fish.

Saving

• The farm saves itself in your browser every few seconds and when you close the tab.
• In the Farm tab you can download a save file, load one, or copy a save code to move your farm to another device or browser.
• Clearing your browser’s site data, or playing in a private window, loses the browser save, so download a save file now and then.