The discovery was made by local people two days ago on Sandy Bay in the Maherees, an island near Castlegregory on the Dingle Peninsula.
The phenomenon has never been seen in the area before, at least not in such huge numbers, but experts believe it is a natural occurrence that may be related to the fine weather over the past few weeks.
The fish are mainly sprat but there are also mackerel among the decaying bodies on the shore that will now have to be disposed of by Kerry County Council.
Peculiarly, no birds or scavengers have eaten the bodies that have been just lying on the shore, rotting, since Thursday.
Locals contacted fisheries expert, Kevin Flannery, the director of Dingle’s Oceanworld Aquarium and the go-to man for all matters marine.
He believes one of two things happened; either the fish were chased ashore by something in the water or else it was caused by a tidal bloom.
“Either they were being chased by bigger fish like blue fin tuna or a shoal of mackerel and got trapped in the corner of the bay and got washed ashore,” he said.
“The other possibility is that because of the fine weather there are a lot of tidal blooms and Noctiluca or night light occurs where the plankton in the water lights up by night.
The phenomena of Noctiluca scintillans is also known as sea sparkle. It causes fluorescent blue patches that glimmer in the water and although it can look magnificent, it can also be potentially toxic.
Sea sparkle can also be triggered by pollution from sources like farm waste where an increase in nitrogen and phosphorus cause the plankton to bloom.
“It’s a beautiful thing to see and not something that occurs too often,” Mr Flannery added.
“With the prevailing southeasterly winds the plankton would have accumulated in the harbour but it would also deplete the oxygen in the water.”
And if the oxygen is depleted in the water, the fish are also starved of air and die.
READ MORE: http://www.independent.ie/irish-news/millions-of-fish-washed-ashore-on-west-kerry-beach-in-strange-phenomenon-31579375.html