Redesigned eel traps have been put in at a hydro-electric dam on the River Erne to prevent a repeat of last year's massive kill of the critically-endangered fish.
Eleven months since 300,000 of the creatures died in traps supposed to aid migration past Cathleen's Falls in Ballyshannon, a redesigned system will be used from St Patrick's Day.
Three new traps will be operated by the ESB at the dam and in the Erne estuary with increased water supply, oxygenation and a new material used inside the traps to make it easier for baby eels to climb in.
The European eel is critically endangered and commercial fishing on the Erne system stopped five years ago under European Union rules to reverse the 90% decline in stocks since the 1970s.
No prosecution has been ordered following the massive kill last April and Inland Fisheries Ireland (IFI) declined to say if one is planned.
"IFI referred the matter to its legal advisers. In view of the fact that the matter is under consideration as regards the possibility of legal proceedings/ prosecution in relation to the fish kill, it would be inappropriate to comment further," it said.
An investigation following the incident last Easter found an exceptional number of juvenile eels entered one trap overnight at the very start of the migration season, exceeding the tank storage capacity.
Hundreds of thousands of the elvers died, weighing a total of 112kg and representing almost 17% of the total run of baby eels into the Erne system.
The creatures take on a mysterious migration when no longer than 20mm.
They travel 4,000 miles on Atlantic currents from breeding spots in the Sargasso Sea to European shores where they live in freshwater for up to 20 years before returning to the same seas to spawn.
The ESB said: "ESB have been very successfully trapping Erne elvers for many decades, since the 1960s, and whilst we are disappointed to have an elver mortality event occur in 2014, ESB will endeavour to continue to facilitate the natural recruitment of juvenile eel.
"The inward migrating elver will continue to be trapped and will complement the ongoing outward migrating silver eel trap and transport system which is being run to facilitate the future conservation of European eel stocks."
Among the changes to the migration system on the Erne are a new trap on the northern shore of the estuary along with an improved inspection regime for ESB staff and changes to checking schedules and local recording and reporting procedures.