Doitsu Koi Breeding Guide

How to breed Doitsu koi (Cyprinus carpio), a scaleless pond egg-scattering line from German carp that spawns in spring; scalelessness comes from selective breeding.

Overview

Doitsu refers to scaleless koi (Cyprinus carpio) derived from the German carp lineage; the colour patterns can vary. Koi are large pond fish, so breeding is an outdoor pond project rather than an aquarium one. All koi varieties result from selective breeding, and the scaleless Doitsu trait is maintained only by systematically culling offspring that do not show it during development.

Conditioning

Koi benefit from being kept in the 15–25 °C (59–77 °F) range, and their immune systems are very weak below 10 °C (50 °F), so conditioning mature breeders in stable, warm-season water supports a healthy spawn.

Breeding Setup

Spawning is set up in a pond with a target for the sticky eggs to attach to. A sticky outer shell around each egg helps keep it in place so it does not float around, so spawning ropes, brushes or fine plants are provided as a receiving surface.

Spawning Behavior & Trigger

When koi naturally breed on their own they tend to spawn in the spring and summer seasons. The male starts following the female, swimming right behind her and nudging her. After the female releases her eggs they sink to the bottom of the pond and stay there, held in place by the sticky shell.

Egg & Fry Care

Koi produce thousands of eggs per spawning, though many of the fry do not survive due to being eaten by others. Because of the high losses, separating eggs or fry from the adults improves survival.

Common Challenges

Even from the best champion-grade koi, most offspring are not acceptable as nishikigoi — they may have no interesting colors or even be genetically defective — so expert culling is required. For Doitsu the goal is a clean scaleless skin (apart from the orderly dorsal and lateral scale rows of the German-carp line) carrying the intended colour.