Very fishy tales, but true ones

THE fact that our lakes and rivers still contain many biological surprises was emphasised recently when it was announced that freshwater jellyfish had been discovered in Lough Derg and Lough Erne.

Tese small jellyfish, the cap is about the size of a euro coin, are natives of the Yangtze River in China but were accidentally introduced into Europe over a century ago.

This is the first time they’ve been found in Ireland, though it’s quite likely they’ve been here for some time. Jellyfish have a life-cycle that involves them living for long periods in something akin to a larval form, called a polyp. In order for this species to develop into a free-swimming jellyfish it needs water temperatures in excess of 25 degrees over a considerable period of time. It was the warm summer that made this happen, and it may not happen again for some years. They’re too small to sting humans and the biologists don’t believe they pose any significant threat to the ecology of our waterways.