An aquatic invasive species forced Montana officials to destroy fish in a state hatchery.

Montana Fish, Wildlife and Parks reports that New Zealand mud snails were recently discovered at FWP's Bluewater State Fish Hatchery south of Laurel. Unfortunately, to eliminate the threat of further spread, nearly all of the rainbow trout and largemouth bass at the facility have to be destroyed.

The tiny nuisances are not new to Montana. New Zealand mud snails are found in a number of bodies of water across the state. They can grow in population and spread very rapidly.

New Zealand mud snails have the potential to change the ecology of water bodies they infest. And, like most AIS, once established they are hard, if not impossible to eradicate. That threat is what forced Montana FWP to be proactive about destroying the fish.

But how did the snails invade a hatchery?

It turns out this is not their first visit to Bluewater. Two years ago, the hatchery went into quarantine and was decontaminated when the snails were discovered. While uncertain, officials think  the new infestation is due to cracks in older concrete tanks. This might have allowed mud snails from the previous infestation to survive decontamination.

The largemouth bass that will be destroyed include brood stock. Some rainbow trout at the facility will be stocked as planned, because they were in an interior part of the hatchery not connected with the area where the mud snails were found. No mud snails were found in the interior part of the hatchery.

This will not be a cheap mitigation. The loss of investment in the hatchery stock, the value of the fish and the cost of decontamination is estimated at $225,000. Montana FWP say they hope the effect on their stocking program will be lessened as much as possible by stock from other hatcheries.

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