• 15 fresh and healthy sashimi-grade tuna recipes

Heidi and Pavo Walker supply fish to many of Australia's best restaurants including Stokehouse, MoVida and Rockpool Bar & Grill. For more than a decade, people have been asking the Queensland-based husband-and-wife team how to buy their tuna to eat at home. The last thing Heidi Walker ever expected to tell them was "visit Coles".

"The coronavirus has turned everything on its head," she says. "Normally, around 80 per cent of our sashimi-grade tuna is exported to the United States and Japan, with the remainder sold exclusively to Australian chefs.

"When the international market collapsed due to COVID-19, and local restaurants were ordered to close, we needed a way to keep our boats fishing and 50 staff employed. Two weeks ago I contacted Coles to see if they could help put our tuna in their supermarkets and they jumped at the chance."

The retail giant will stock the Walkers' fresh yellowfin tuna steaks in 150 stores across NSW, Victoria and Queensland from Wednesday. Processed in Mooloolaba and certified sustainable by the Marine Stewardship Council (MSC), the tuna is priced at $35 a kilogram - about half the cost of sashimi-grade yellowfin before the coronavirus pandemic.

"We know many businesses have been impacted by recent events forcing restaurants to close and we're delighted to partner with Walker Seafoods to support them during this time," says Coles general manager Charlotte Gilbert.

"We've also recently begun stocking Western Australian crayfish in selected Coles delis, and partnered with Far West Scallops for the supply of premium Shark Bay scallops."

Walker says she hopes to continue working with Coles after "everything returns to normal".

"We want the tuna to be accessible to all Australians, while also being ready to support chefs when restaurants reopen. It's likely we'll export less."

Members of the Melbourne public can also buy Mooloolaba yellowfin from The Fish Shoppe in South Melbourne Market, Collingwood's Ocean Made Seafood, and Red Coral wholesalers in Bayswater. All vendors are providing home delivery during the pandemic with a bounty of other premium seafood usually exclusive to restaurants.

"We've just listed MSC-certified Glacier 51 toothfish for retail sale, plus marbled Ora King salmon from New Zealand," says Red Coral sales manager James Marinopoulos. "The salmon has been going especially gangbusters with customers."

Through its Melbourne Food Squad online marketplace, Red Coral is also selling scarlet prawns sourced from waters off Queensland. The foot-long prawns have the delicate taste of sweet lobster and are best eaten raw.

"A sashimi platter of scarlet prawns, Mooloolaba yellowfin and Ora King salmon is for all time," says Marinopoulos. "Only a month ago it would have been almost impossible to create at home. Now people can have all that premium seafood delivered to their door."

In Sydney, hatted chef Josh Niland used Mooloolaba yellowfin to make a version of chilli con carne on Thursday, available as a take-home dinner from his Fish Butchery shop in Paddington. Joto Fresh Fish also sells Walker tuna to the public through its online store, as does MooFish and Martin's Seafood.

"It's a world-class product," says Costa Nemitsas, general manager of Martin's Seafood, which is now opening its Botany warehouse to the public every Saturday morning. "People can buy our seafood for exactly the same price restaurants were paying."

The "baller fridge" at Martin's contains premium seafood such as Yarra Valley salmon caviar, Pambula rock oysters, Clarence River baby octopus, Pilu bottarga and Cape Moreton scarlet prawns.

"I've sold more scarlet prawns to punters over the past three weeks than what I sold to chefs in the two months before all the restaurants were forced to close," says Nemitsas.

Cooking yellowfin tuna at home

Sashimi-grade yellowfin tuna is a versatile fish, delicious raw and lightly seasoned, or cooked and enhanced by bold flavours such as wasabi, olives, turmeric and ginger.

"At Rockpool Bar and Grill, we buy whole yellowfin from the Walkers and break it down into different parts," says the restaurant's head chef Corey Costelloe. "The belly might be sliced and slightly blow-torched to bring out its fat, while the collar is used for tartare and the loin is turned into steaks."

Costelloe says the key to cooking a perfect tuna steak is to only pan-fry one side..

"You want to bring the tuna to room temperature first and season it with salt. Meanwhile, have a plate warming in the oven. Get a pan really hot and sear one side of the tuna until it has little bit of colour. Remove it from the pan and place the other side on the warmed plate. Heat from the plate should warm the tuna just enough that one side is rare and the other is nicely flavoured from the pan."

Spice rubs and marinades are encouraged too, says Costelloe, but should not contain too much sugar. "Unless you're cooking over a charcoal grill, the sugar will burn when it hits a high heat."