Marine Harvest, which operates in Mulroy Bay, lost the fish in a kill off the Co Mayo coast.
The firm opted for an accelerated harvest at its Donegal aquaculture farm in order to minimize losses on its farmed stock, it said.
Scientists connect the the jellyfish invasion to warmer sea waters. The mauve stinger (Pelagia noctiluca) has killed salmon before off our coasts.
It is a phenomenon that has also been observed in other parts of the world.
Marine Harvest has been taking preventive measures such as giving its salmon less fish feed to keep them less active with gills covers closed as it worries about strandings of this jellyfish species from Donegal to Kerry.
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