How to Know If Koi Will Lay Eggs

Koi are egg-laying cold-water fish, which were bred from carp. Koi have long lives and only reach sexual maturity after a number of years. Koi that are four to five years old and 20 to 24 inches long are the best candidates for a successful breeding program. The fish typically prepare to breed as the weather gets warmer. Dr. Bertrelle Caswell, former chairperson of the Associated Koi Clubs of America, believes these fish may synchronize their breeding with the full moon.

Things You'll Need

  • Koi pond with clear water
  • Adult male and female koi
  • Spawning mop
  • Koi keeping manual (optional)
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Instructions

    • 1

      Observe your koi closely during the winter months so you have a clear picture of what each adult looks like during the non-breeding season. This will help you see the physical differences that appear during early spring when the koi prepare to spawn.

    • 2

      Observe your koi at the beginning of spring for signs of breeding behavior and physical changes to their bodies. Male koi will develop slightly raised, cream-colored bumps on and around the hard gill plates and along the ridge of his side fins. Place a spawning mop in your pond.

    • 3

      Continue to watch the koi closely every day. Female koi begin to fill out and take on a rounded appearance as the roe develop within their bodies.

    • 4

      Look for the appearance of a rounded section on the egg-carrying female, which will be noticeable around her center. In most cases, the female appears to be rounder on one side, when viewed from above.

    • 5

      Watch for spawning behavior. When a female is ready to release eggs she will swim into and around the spawning mop.

    • 6

      Male fish will be encouraged by this behavior and will swim toward the mop and the female. One or more of the males will swim repeatedly into the side of the female to force her to release eggs. Apart from ramming the female, males will also try to drive her against the side of the pool. The male fish will also be releasing sperm into the water.

    • 7

      Continue to observe the mating behavior. In all cases, the fish that is being rammed is the female, and she is about to release her eggs.