Breeding Koi Basics

You've tried your hand at keeping kois and now, you want to breed them. Whatever your reason in propagating them, here's the lowdown on koi procreation.

Choosing parents

A lemon tree won't produce apples, so it is with kois. Excellent quality parents will deliver excellent quality fingerlings. In fact, if you have a good stock of koi parents, you may want to keep them around for a while.

Breed the healthy ones, in the variety, colorings and markings you want. The kois should be at least 10 inches (25 cm) long, about 3 to 5 years old for males and around 4 to 6 years old for females.

The age of the female at spawning time is crucial as it determines eggshell quality. A koi that's too young delivers eggs with thinner shells, negatively affecting survival. On the other hand, a female that's too old will have thicker shells; the male's sperm will have difficulty getting through it.

Spawning

Condition your kois a year before they are bred. The most ideal season for breeding kois are from spring (in April) until midsummer (about July), when they're at a feeding frenzy.

Kois must be isolated from each other for a month and kept unfed for a few days before mating for optimal spawning. This decorative carp spawn best during a full moon, and can release eggs in the early hours of the morning (around 2 a.m.) until 9 a.m. a day or so after the male has been introduced to the female. Make sure there's a ratio of 2 males to 1 female in your spawning tank as a large female koi can lay about 300,000 eggs at a time.

How will you know when the kois ready to mate? For the male, all you have to do is feel their pectoral fins and their gills. You'll feel rough spots around these areas, like a day's growth of beard. For females, it's more difficult.

Females are more rounded, especially when they're in season. The males, on the other hand, are slender throughout. If you need to be sure, press the koi's abdomen gently. If it's a female, eggs will come out. But be very careful so as not to hurt the koi.

When it's spawning time, the males nudge the females with their spotty pecs and gills—sometimes a bit roughly—to expel the eggs. Once the eggs are out, the males fertilize them with their sperms. The fertile eggs are clearer; the infertile ones are usually opaque.

Eggs are quite sticky so you'd need spawning spots where they can adhere to. These 'nests' could be any media like a frayed rope, evergreen, or pond grass. What's important is that the eggs are immediately separated from the parents as they can end up as fodder for the hungry mates. Also, cover the spawning tank with a net to protect the eggs from predators.