THE commercial fishermen who blew the whistle on what they call an environmental disaster in Gladstone Harbour say dead fish will soon wash up on its shores.

They insist sick, blind and ulcerated fish were being pulled out of the harbour for months ahead of last week's official ban by the State Government.

Operators say they were working alongside Queensland Fisheries officers, who were monitoring possible turtle kills, when they dragged sick and slime-covered fish from waters around Gladstone Harbour.

The fishermen say the Government acted only after it was presented with an ultimatum a fortnight ago that they would go public with their concerns. The ban was slapped on 24 hours later.

A dozen fishermen have reported being ill from handling the fish, along with the pregnant wife of a deckhand and their two young children exposed when they met their dad when his boat was pulled ashore.

At least two of the fishermen have spent time in hospital, including Tannum Sands operator Trevor Falzon, who spent five days on a drip.

Mr Falzon said fishermen had no option but to act, fearing children would be exposed to the toxins during the school holidays.

"I couldn't walk," Mr Falzon said. "I spent five nights in the Mater Hospital in Gladstone. It cost $5800. My foot was flaming red. I had a temperature of 39C."

On Friday, Fisheries Queensland released findings that the dead fish had been attacked by a mystery parasitic fluke that was sending them blind.

They were also suffering from red spot, a disease usually found in Queensland waters after the first heavy rains of summer or during lean winter times.

But the cause of the outbreak was yet to be confirmed.

Fisheries Queensland's Dr John Robertson said red spot disease could develop into burn-like marks, or ulcers with red centres.

He said more research was needed into the parasite, which affected the eye of the fish.

"We now know that this parasite is what has been causing the cloudy eyes in some barramundi in the area," he said.

Additional testing is being conducted on new samples of other fish species, prawns and mud crabs but results are not expected for several weeks.

Until then, the fishing ban remains.

Fourth-generation fisherman Chris Sipp believed dredging was to blame.

He said the fish were fine in clear reef water but became stressed as they approached Gladstone harbour. Once in the port, they "roll" - die and go belly-up.

"We are devastated at the situation here in Gladstone but we know that we have done all the right things to advise all government authorities to keep people safe," he said.

Queensland Seafood Industry Association president Michael Gardner said the dead turtles, dugongs and fish found in the Gladstone area were "an environmental disaster".

He said the sick and dead animals coincided with dredging by Gladstone Port Corporation working on the massive LNG plant and pipeline being built in the harbour.

But the port corporation says they are not to blame.

Chief executive officer Leo Zussino said dredging was tightly controlled. He said the sick seafood had been fished out of the harbour before dredging began.

The corporation says the harbour has been dredged in the past without any impact on fish. Instead, it blames fresh water from the floods earlier this year hurting marine life.

Mr Zussino said the dredging had not stirred up contaminants because testing showed there were none on the harbour floor.

"A lot of people say there's been contamination in Gladstone harbour for a century. That's simply not true," he said.

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Originally published as Toxic harbour catch makes fishermen ill