Scientists plan to release 70,000 young wild eels into the River Lagan system in a bid to reverse a massive decline in the species.
Some 6,000 glass eels (young eels) sourced from the River Severn have already been released into Hillsborough Lake by scientists from the Agri-Food and Biosciences Institute with the help of the Lough Neagh Fisherman's Cooperative Society Ltd, which owns the largest eel fishery in Europe.
AFBI said the release is a long-term experiment to see how the eels will eventually contribute to the European spawning stock in years to come.
Some eels have been marked so that their progress can be tracked, potentially over the next 20 years.
Eels had dwindled to very low numbers in the River Lagan system, mirroring a Europe-wide decline that has seen eel fishing banned in many countries.