An introduced species of barnacle and poor maintenance have been blamed for the mass escape of 20,000 farmed kingfish at Port Stephens in New South Wales early this year.

The founder and majority owner of the Huon Aquaculture Company, Peter Bender, has spoken for the first time about the January 18 storm which damaged one of the sea pens in a farm trial 6 kilometres offshore at Providence Bay.

Huon is conducting a five-year kingfish trial at the mid-north coast site with the NSW Department of Primary Industries.

Mr Bender said a 6-metre swell and some individual waves up to 11 metres were monitored in the storm but the company's sea pens were built to withstand worse.

"Basically the cages themselves were fine, what actually happened was really we were probably not aware of some of the maintenance issues we had to do here," Mr Bender said.

"In Tasmania, we have different sorts of fouling on the nets, what we found up here, we got a lot of barnacles as well as mussels on the nets and particularly on the predator nets and that weighed it down a lot."

The unexpected barnacle growth was an introduced species which most likely came from ballast water in ships using Newcastle harbour, he said.

"The barnacles were cutting through the ropes that held the net in place particularly in that rough weather, it's one of those things, we learn as we go along and that's why were doing a trial here, we only wanted to have a few pens up here, we only had three pens of fish and we've learned a lot from that, so now it's a matter of getting some equipment that'll take that fouling off the nets," he said.

Mr Bender said the company recovered more than 5,000 fish and the remaining survivors provided a bonanza for local anglers and commercial fishers.

"I don't think there'd be too many issues, the kingfish were native to here, the brood stock we're using are from this area so they're a native fish, it's not like we've let go an exotic species of fish or anything," he said.

"So, these fish are readily available in this area, we tend to find that fish that have been fed on pellets don't really forage much for other sorts of live fish, so I think we'd find most of the fish would probably have been caught anyway."

The executive director of NSW DPI Fisheries, Dr Geoff Allan, said he was confident that new net cleaning equipment bought by Huon would greatly improve the integrity of the sea pens in rough weather.

"This is what a trial is for, to try and find the weaknesses in the project and when you find the weaknesses to readjust in our case the strategy for the long-term future to make sure it doesn't happen again," Dr Allan said.

"So it's very unfortunate the fish escaped, certainly for Huon, who no longer have those fish to sell but we have learned from that lesson and have adjusted the strategy going forward."

Huon's sea pens are built to withstand storms. ( ABC News: Sean Murphy )

Lack of independent scrutiny

According to one of the key critics of the joint venture, there has not been enough independent scrutiny of the fish escape or of the ongoing management of the project.

Frank Future is a tour boat operator at Port Stephens and chairman of the local marine park association, which supports the biggest protected reserve in NSW.

"The problem with DPI Fisheries being involved as a proponent with Huon is that there's no independent arbiter and when something like this happens you're appealing to Caesar, you know, the Government themselves are driving the project so there's no-one over the top of it," Mr Future said.

While there were only a couple of pens operating now, he was concerned about the impact of an expanded industry on Port Stephens' $500-million tourism industry.

Dr Allan said the fish escape was being investigated by the Department of Planning and Environment, which approved the trial farm.

The University of Newcastle was providing independent analysis of water quality and environmental impacts on the sea floor. Conditions had also been set by the Commonwealth Department for Environment and Energy.

The DPI was providing the scientific support for the project to find solutions for the state's over-reliance on imported seafood, which had grown to 85 per cent of the market, he said.

"We've learned a lot, we've learned we can produce the fingerlings and supply them in cages, they've had no issues there," Dr Allan said.

"We've had no issues to date with pathogens or disease, the fish grow very rapidly, in fact more rapidly than our initial models suggested. Their feed conversion ratios and their feeding is quite effective in the cages."

Feeding frenzy in a sea pen — the kingfish have grown faster than expected. ( ABC News: Sean Murphy )

Kingfish industry expected to grow

Both the DPI and Huon were acutely aware that any future kingfish industry would have to earn a social license, he said.

"In general we've tried to be very transparent in the consultation phase and now during the results phase," Dr Allan said.

"This all hinges on social license. We really want the public to know we are trying to address a key concern in this state, which is lack of seafood production.

"We're trying to do that in an environmentally sustainable and economically viable way and that's the whole purpose of this venture. If we fail those tests then ultimately the strategy shouldn't go ahead."

Mr Bender said his company was keen to diversify into a white flesh species to complement its Tasmanian salmon production and he was confident it could develop a sustainable, environmentally-sound kingfish industry in NSW.

"The market potential is certainly there, there's huge demand for a white fish that can be in the market every day of the year," Mr Bender said.

"The problem with wild-caught fish is it can be there some days and then not others, whereas this can be a reliable, good-quality white flesh fish that's very versatile from sashimi to various ways of cooking it you know, like we've done with salmon.

"People weren't used to eating salmon when we first started, the first year we produced salmon the whole industry only grew 50 tonnes and struggled to sell it but now the whole industry grows about 60,000 tonnes and we can't grow it quick enough now, the demand is increasing every year, and we see the same sort of thing happening with kingfish once it's more available."