Barramundi farmers are appealing to consumers to eat more Australian-grown barramundi, with some facing a shortage of space as demand dries up and fish keep growing.

Like many industries, the country's barramundi farmers took a hit when the restaurant and cafe trade closed in March due to coronavirus restrictions.

At Coral Coast Barramundi at Bowen in north Queensland, about 1 million barramundi fingerlings are grown every year by a team of staff and marine biologists, to stock dams for anglers and supply the food service industry.

Farm manager Justin Forrester said while the cooler winter conditions did slow the growth of barramundi, there was still a looming deadline.

"We can try to slow them down so they fit in the ponds, but eventually they keep growing and the ponds have only got so much space, so much electricity, and so much room, to keep the fish healthy and in good condition," Mr Forrester said.

The aquaculture operation usually harvests about 25 tonnes of fish from the ponds every week but, when the food service industry closed under coronavirus restrictions, demand dropped to about 8 tonnes per week.

The drop in demand also meant a drop in available work for staff, some of whom have worked at the site for years.

At Australia's largest barramundi farm, at Humpty Doo near Darwin, farm manager Dan Richards said they were not short on space but the pandemic had had a big impact on their bottom line.

Free fish to those in need

Even at the height of the coronavirus crisis, there has been generosity and kindness from people and businesses.

Mr Richards said when their team saw the impacts of the virus on the community, they were looking for ways to help.

Humpty Doo Barramundi donated about 10,000 kilograms of fish, which was used in food hampers and prepared meals for people in need in major cities.

"[We chose to donate] where people were looking to support the people in the food service industry who were out of jobs and the like," he said.

"We've really seen that as an area that's part of our core business and people who we can really support at this time."

Coral Coast Barramundi also donated fish, working locally to donate to healthcare workers at hospitals in the region.

Now, they're hoping consumers will return the favour, as Mr Forrester says he hopes to never see a crash in the market like this again.

"We're going to hopefully come out the other side," he said.

"If Aussies get behind us, buy a little more farmed barramundi, we'll definitely, hopefully, get across the line."

'Get out and buy barramundi'

Owner of Coral Coast Barramundi and president of the Australian Barramundi Farmers Association Ken Chapman believes the best thing to help right now would be for more Australians to buy Aussie-grown barramundi.

While there is a roadmap for the gradual reopening of restaurants as restrictions ease around the country, it's not enough for an immediate increase in demand.

"We haven't seen any change as yet, we're hopeful that [we'll] come back with strength as the year progresses," Mr Chapman said.

While barramundi is a recognised Australian species, most of the fish available in Australia is foreign.

Mr Chapman hopes consumers will look at where the barramundi comes from and support Australian-grown.

Woolworths said since 2018, it had doubled the volume of fresh Australian barramundi it sold and was the largest retail seller of the fresh fish.

Coles did not respond to the ABC.