10 Large Koi Vanish From Netted 7,000-Gallon Pond: The Mystery Deepens

A pond owner in NW Massachusetts discovers all 10 remaining koi (18–20 inches) gone from a 7,000-gallon, 4-foot-deep pond. The net cover had one 18-inch gap. No bodies, no disturbed sediment, no net damage. Three koi died naturally over winter and were found floating. The rest? Vanished.

Predator Profiles: Who Could Do This?

• River otter: Efficient, takes multiple large fish, leaves little evidence. Can slip through small gaps. But owner says no otters locally.
• Fisher (fisher cat): Agile, semi-aquatic, takes large prey. Could exploit the 18" gap. Rarely seen, but present in MA.
• Great blue heron: Spears fish through netting, but bodies remain under the net. Doesn't remove 10 large koi cleanly.
• Raccoon: Makes a mess—scales, parts, torn liner. Unlikely to enter 4-ft water.
• Human: "Koi-napping" happens. Expensive koi are targets. The net was "put back"—by whom?

Critical Questions

1. Did fish disappear all at once (under ice) or gradually?
2. Was the pond checked daily, or only after thaw?
3. Any tracks, scat, or disturbed vegetation around the gap?
4. Security cameras? Motion-activated trail cams are cheap and revealing.

Immediate Actions

• Secure the net completely—no gaps >2 inches.
• Install a night-vision trail cam ($50–100) aimed at the gap and pond edges.
• Consider electric fencing (low-voltage, pet-safe) around the perimeter if predators persist.
• Don't restock until the culprit is identified.

The Uncomfortable Truth

If the net was secure except for one gap, and 10 large koi vanished without a trace, human theft is a real possibility. Koi that size are worth hundreds each. A motivated thief with waders and a net clears a pond in minutes.

For now, net it tight, camera it up, and hope the camera solves the mystery. Some pond enigmas remain unsolved—but most have a terrestrial explanation.