Koi Mud Ponds in Japan
- Kevin Warren
- 1 minute ago
- 3 min read
1. What a Mud Pond Really Is
A mud pond (dochi-ike) is an earthen growth pond shaped by geography and tradition:
Clay bottom rich in minerals
Snowmelt or mountain runoff supplying soft, clean water
Natural food web of plankton, insects, crustaceans
Large space with low stocking density
Minimal disturbance from June to autumn
Koi Mud ponds in Japan are not ornamental. They are working agricultural ponds designed to grow koi the way rice fields grow crops: slowly, naturally, and with deep knowledge of the land.
Breeders use them because the results cannot be replicated in concrete or fiberglass systems. The clay supports skin luster, the natural diet builds body mass, and the seasonal rhythm shapes the future quality of the fish.
Key benefits and risks of mud pond growth
Benefits
• Enhanced growth & body development: More space, natural feeding, less stress = better body shape and potential.
• Improved skin & colour quality: The interaction of soft water, clay minerals and natural diet supports deep red (beni) pigment and good white (shiroji) ground in koi.
• Stronger immune resilience: It’s argued that koi raised in more natural ponds (with microbial and faunal activity) are more robust against parasites and environmental stress.
Risks /Challenges
• Water-quality variation: Because mud ponds rely on natural processes, they can be subject to pH swings, acid rain, temperature variation, and unexpected turbidity changes.
• Predation and environmental exposure: Larger ponds in rural settings may expose fish to predators (birds, mammals) or loss of feed/nutrient control.
• Harvest timing and commercial pressure: The period of harvest is intense; if koi are left too long or harvested too early, body and colour may not reach full potential.
• Not all mud ponds are equal: Soil composition (clay type and mineral content), water source, bottom depth, and prior use matter greatly. Hobbyists trying to replicate the effect often find variable results.
2. The Annual Cycle of a Niigata Mud Pond
Understanding ikeage begins with understanding the year leading up to it.
Spring — Spawning & First Culls
Parent koi (oyagoi) are selected, spawned, and watched closely. Fry are culled repeatedly until only a few percent remain. For more on this topic visit The Art of Sorting Fry elsewhere in Koi Waters Online Magazine
Summer — Stocking the Mud Ponds
Mid-May and June are usual times Koi enter ponds. By this time breeders have filled ponds, tested water, and established a natural plankton bloom. An important factor for the timing of koi entering the mud ponds is temperature. Ideal water temerature is between 24–28°C. Once stocked, ponds are monitored, nurtured and closely watched. Concern for the breeder is water temperature.
At 30°C and above, dissolved oxygen becomes a limiting factor, and feeding must be cut back. Past 32°C, feeding is usually halted entirely. Fry can tolerate higher temperatures thanks to their shallow, heat-absorbing ponds. Larger
Koi, however, demand far more oxygen and absorb it more slowly. And while high August temperatures might sound beneficial for growth, they often coincide with water sources drying up. When inflow is limited, breeders become especially cautious, reducing food to safeguard water quality.
July–September — Natural Summer Growth
Koi grow under soft mountain water, sunlight, and natural food. Breeders monitor oxygen, temperature, rainfall, and the supplemental feed their automated feeders provide — but the ponds themselves stay quiet.
October — November Harvest Season (Ikeage)
As temperatures cool, ponds are drained and seined. This is when the year’s work becomes visible. Japan's main ikeage season runs from late September to November dependent upon weather, overall development or outside circumstances.
Winter — Rest & Selection
Koi Breeders evaluate each koi, plan future pairings, and prepare selected fish for the spring market or shows.
The Tradition Endures
Despite modern filtration systems and indoor technology, Japanese Koi Breeders continue to trust mud ponds because the land itself shapes the koi. Snowmelt water, mountain minerals, and quiet summer months cannot be engineered. They must be lived.
Koi Waters Online Magazine would like to thank the following Koi Breeders for allowing me to photograph at their facilities. 本当にありがとうございます。敬意を込めて。
