Preliminary results from the investigation into the major fish kill at Inver Bay, Co Donegal, indicate a "combination of causes", some of which may be naturally occurring.
Results of several key scientific tests are still outstanding, and it may be some days before the Department of Communications, Marine and Natural Resources can draw any final conclusions. However, it is understood that an algal bloom has been ruled out.
Some 345,000 fish on three fish farms perished over a seven-day period, but the remaining stock on site are now recovering.
The Irish Salmon Growers' Association (ISGA) maintains that trawling for prawns was the main cause of the kill, when mud or silt was disturbed and released hydrogen sulphide.
This, in turn, suffocated fish, which showed substantial damage to their gills. Some 560 tonnes of fish had to be removed and disposed of, supervised by the Marine Institute.
The ISGA says it had raised the issue of trawling close to the fish-farm cages on numerous occasions in recent years, and says the Minister for the Marine has a duty to protect fish farms under 1997 legislation.
"The Minister's Department was very slow to respond to this latest crisis, and its main concern now seems to be how the dead fish are being disposed of," Mr Richie Flynn, chief executive of the ISGA, said.
"It doesn't seem to have any concern for the three fish farms, and the 50 people directly employed on these farms.
"Either the Government supports fish farming or it doesn't - and I'd like to see what industry it would put in these areas in its place," Mr Flynn added.
The scientific results so far include chemical and other data. Trawling in Inver Bay is also being examined as part of the investigations, led by the Marine Institute.
Possible sabotage was ruled out early on in the investigation due to the location of the fish farm sites across Inver Bay. The Lough Swilly Preservation Group has called for an independent inquiry into the fish kill, one of the largest ever on an aquaculture site in Irish waters.