THE disease affecting fish in Gladstone Harbour has been identified, but its cause remains unknown.
Red-spot disease and another parasite have been identified as the two conditions striking fish around Gladstone Harbour and leading to its closure for fishing.
But the community will have to endure further confusion as the cause remains unidentified.
Fisheries Queensland general manager of habitat and assessment Dr John Robertson said red-spot disease was endemic and seen in Queensland waters occasionally.
"In Queensland, red-spot disease usually occurs either during winter months when the immunity of the fish is lower, or following the first heavy rainfall of the wet season," Dr Robertson said.
"It is typically caused by a fungus and often occurs in fish when they are under stress."
He said there was still no clear answer as to what was causing the current outbreak of red-spot disease.
The separate parasite remains unexplained.
"We now know that this parasite is what has been causing the cloudy eyes in some barramundi in the area," he said.
"We still have more to learn about this condition and how it is affecting fish within the area."
Testing is being done on new samples of other fish species, pawns and mud crabs.
Those results are not expected for several weeks.
The Observer understands some 15 people have had side effects apparently caused by contact with diseased fish.
Queensland Health could not confirm the number of people but said it had not established a link between handling diseased fish and any adverse effects on humans.