How Long to Quarantine New Koi?

By KoiQuanta Editorial Team|Updated Mar 2026

The direct answer: Minimum 21 days for domestic koi from a reputable dealer with documented quarantine history. Minimum 42 days for Japanese imports, show fish, unknown sources, or any fish going into a pond with high-value established fish.

Most professional koi dealers and serious collectors use 42 days as their standard, full stop. The 21-day minimum is the floor, not the recommendation.

TL;DR

The short answer is 21-42 days - here's how to choose the right window.
Minimum 42 days for Japanese imports, show fish, unknown sources, or any fish going into a pond with high-value established fish.
Most professional koi dealers and serious collectors use 42 days as their standard, full stop.
The 21-day minimum is the floor, not the recommendation.
Anchor worm and koi lice take 3-4 weeks to reach a visible stage.
A 21-day quarantine at 50°F is essentially meaningless for KHV observation - you're just holding fish in cold water.
Summer quarantine at outdoor temperatures (80°F+) should still be done, but watch more closely and be prepared to act faster.

Why 21 Days Is the Floor, Not the Target

Twenty-one days at 65-68°F covers:

Most external parasite lifecycle windows (Gyrodactylus at 3-5 days, Dactylogyrus at 7-10 days, ich at 10-14 days)
The most common KHV incubation period (7-14 days at peak expression temperature)
Initial bacterial infection observation window

But "most" and "common" aren't "all." KHV can have an extended incubation. Anchor worm and koi lice take 3-4 weeks to reach a visible stage. And fish that have been through import stress, show stress, or have unknown health history need more observation time, not less.

Source Determines Duration

| Source | Minimum Duration |

|--------|-----------------|

| Reputable domestic dealer with documented 42-day quarantine | 21 days (you're extending their protocol) |

| Domestic dealer with unknown quarantine history | 28-35 days |

| Online purchase, shipped fish | 35-42 days (shipping adds stress and disease risk) |

| Japanese import | 42 days minimum |

| Fish show or auction | 42 days |

| Unknown source (rescue, rehome, trade) | 42-60 days |

Temperature Determines Accuracy

Quarantine duration only means something if the temperature is right.

65-68°F (18-20°C) is the target. At this temperature:

KHV expresses clinically if present (the virus is in its active replication window)
Parasite lifecycles are slow enough to observe but complete within the quarantine window
Fish immune function is good - the fish can actually fight disease and show you signs

Below 55°F: KHV will not express. Parasites reproduce much slower. A 21-day quarantine at 50°F is essentially meaningless for KHV observation - you're just holding fish in cold water.

If your quarantine tank is unheated and you're doing winter quarantine, add a heater or recognize that your "quarantine" is incomplete.

Above 75°F: Parasite reproduction speeds up, bacterial infections progress faster. Summer quarantine at outdoor temperatures (80°F+) should still be done, but watch more closely and be prepared to act faster.

Discharge Criteria - Duration Alone Isn't Enough

The clock running to 21 or 42 days doesn't automatically mean the fish are ready. All of these must be true before releasing fish to a display pond:

No mortality in the past 14 days
All fish eating normally
No signs of disease, parasites, or behavioral abnormality
Ammonia and nitrite at zero
Any antibiotic courses completed
14 clean days post any treatment

If a fish was sick and treated on day 15, the clock restarts. You don't count from the original arrival date to day 21 and call it done.

The Real Cost of Shortening Quarantine

One disease introduction to an established pond:

Can kill fish worth thousands of dollars
Takes months to resolve (treatment, QT of display fish, system sanitization)
Damages your reputation as a dealer if it happens post-sale
In KHV outbreaks: may require full depopulation

A 21-day quarantine that becomes a 42-day quarantine costs you three extra weeks. That math should be easy.

FAQ

How long is the minimum koi quarantine?

Twenty-one days at 65-68°F with all discharge criteria met is the absolute minimum for low-risk domestic fish. Most professional dealers use 42 days. For imports, show fish, or unknown-source fish, 42 days is the floor.

Does water temperature affect how long I need to quarantine koi?

Significantly. Below 55°F, KHV won't express in infected fish, making cold-temperature quarantine unreliable. Parasite lifecycles also slow dramatically, meaning you need more time to observe through a complete cycle. Heat your quarantine tank to 65-68°F year-round for a reliable, consistent observation window.

When is it safe to add koi to a pond after quarantine?

When all discharge criteria are met and the minimum duration has passed. The fish should be eating normally, showing no signs of disease, and have had clean water parameters throughout the final two weeks. Gradual temperature acclimation to the display pond temperature is good practice, especially if the pond and quarantine tank are at different temperatures.