Koi Disappearing: Predators or Hiding?

Six Koi Reduced to Two: Solving the Mystery

A pond loses 4 koi with zero traces. A "Koi Dome" (underwater shelter) was added, but two more vanished. Likely predators: herons (swallow whole, no trace) or raccoons (usually leave evidence).

Diagnostic Questions

• Pond size, depth, and koi size?
• Is water frozen? (Herons hunt in open water.)
• Could koi be hiding in the dome or plants?
• Any heron sightings? (Dawn/dusk.)

Predator Profiles

• Great Blue Heron: Swallows fish up to 12–14" whole. Leaves no scales, no disturbance. Most likely if koi are 8"+ and pond is open.
• Raccoon: Messy eater—leaves heads, scales, carcasses. If no mess, less likely.
• Otter/Mink: Rare but possible; eat entire fish.
• Cat: Takes small fish; leaves remains.

Effective Deterrents

1. Pond netting: 100% exclusion. Use rigid frame or taut net over entire pond.
2. Electric fence: Low-voltage around perimeter (heron/raccoon).
3. Motion-activated sprinkler: "Scarecrow" type.
4. Heron decoy: Move daily; limited effectiveness.
5. Deep refuges: 4+ ft depth with caves/PVC pipes.

Net the pond now. If koi are small (<6"), bring indoors temporarily. See Why Fish Disappear.