A Tasmanian oyster as long as a ruler and weighing up to one kilogram is one of the more unusual pieces of seafood chef Stephen Nairn has handled in his 19-year career. The XXXL Pacific oyster on the menu at upscale Yugen in South Yarra has presented him with many challenges, the least of which is getting it in and out of the oven.

The identity of the diver who collects the oysters is a mystery, and Nairn doesn't know when he'll get his next delivery. Then there was figuring out how to cook the jumbo shellfish, which sometimes sell for $75, a price tag befitting their size. But prices are also rising on more common oysters due to a drop in supply.

Nairn says when he saw the "comical looking" XXXL oyster at D&K Live Seafood in Footscray, he knew he had to put it on the menu at Yugen, where he's culinary director. It's the only Melbourne restaurant that serves them.

"I love things like that: things that seem like hard work so people overlook it," Nairn says.

Several uncommon oyster varieties are appearing around Melbourne as the industry charts new waters and chefs navigate reduced supply of popular varieties, such as Sydney rocks, due to rains, fires and disease.

CBD cocktail and oyster bar Pearl Diver always tries to have four different oysters on its menu. Right now, though, it's restricted to just two, including a rock oyster from Albany, Western Australia, a region not often represented on menus this side of the Nullarbor.

"It's the first time we've really had rock oysters in decent quantity from somewhere outside New South Wales," says co-owner Pez Collier.

Historically, NSW has been the engine room of Sydney rock oyster production, but in the past three years it's battled everything from heavy rains, which inhibit oyster growth, to diseases wiping out approximately 15 per cent of production.

A Sydney rock oyster takes three years to grow, meaning supply will be restricted until at least 2025.

Fewer Sydney rocks creates an opening for other oysters on menus, including the angasi, another native variety which is being revived in Victoria and served at Montalto in Red Hill during the oyster's May to November season.

"It's a bit much raw," says culinary creative director Matt Wilkinson of the larger, more earthy oyster, which he serves warm.

Akoya, a byproduct of the pearling industry, is slowly becoming more common, too. But because these species are less familiar than Pacifics and rocks, consumers are not yet jumping at them.

"You're less likely to sell half a dozen akoyas than half a dozen oysters," says MoVida chef-founder Frank Camorra. "[Traditional] oysters are a really wonderful way to start a meal before you even look at a menu."

That ritual is becoming more expensive. Federal government forecasts for 2021-22 included a 3 per cent increase on farmgate oyster prices, but every venue interviewed for this story spoke of increased wholesale prices in recent months.

Collier says prices were up 20 to 25 per cent due to three years of La Nina weather and higher freight and transportation costs.

The average price for a single natural oyster in Melbourne restaurants is now hovering around $6. More unusual oysters such as angasis fetch more like $7 at Montalto, while the super-sized oyster at Yugen is sold by weight, with prices varying from $37 to $75.

Oyster farmer Brad Verdich says there's a price correction now taking place for Sydney rocks.

"Consumers have to understand that Sydney rock oysters take three years to grow. That comes with a cost. It's a change in mindset from [seeing] Sydney rock oysters as a loss-leading commodity to a rarity only found in 42 locations on the east coast."

Chefs including Wilkinson say they're happy to pay for quality because oysters are a labour-intensive product to produce.

"It's not a quick turnaround. They're not tomatoes in a greenhouse, or hens in a shed laying eggs each day. They go into the water and problems can happen."

Where to eat oysters in Melbourne

THE DEALS

Bar Romanee
Clear your diary from 3pm-6pm and make your way to this mod bistro for half-price oysters ($3 ea) and $10 spritzes. Available Thursday to Monday.
25 Anderson Street, Yarraville, barromanee.com

Fitzroy Town Hall Hotel
Half a dozen oysters and a glass of something cold are all yours for $20, 3pm-6pm Wednesday to Friday.
166 Johnston Street, Fitzroy, fitzroytownhallhotel.com.au

Arbory Bar and Eatery
Every Thursday at 6pm, the oyster cart rolls around the venue shucking $2 Pacifics to get your weekend off to an early start. Available until sold out.
1 Flinders Walk, Melbourne, arbory.com.au

Philippe
Get $2 oysters in the bar from Tuesday to Saturday, an unlikely bargain in a setting this refined. The French restaurant reopens March 7 following renovations.
115 Collins Street, Melbourne, philipperestaurant.com.au

THE UNUSUAL

Montalto
Try Victorian angasis either in a light tempura batter, poached with bacon vinaigrette or crumbed and crowning a Caesar-inspired salad.
33 Shoreham Road, Red Hill South, montalto.com.au

Yugen Dining
Highly seasonal, the XXXL (market price), warmed and dressed with ginger, spring onion and soy, has to be seen to be believed. Or there are Pacifics with yuzu granita.
605 Chapel Street, South Yarra, yugendining.com.au

Flower Drum
Akoya (pearl meat) is a signature entree, paired with spring onion, garlic chives, asparagus and oyster sauce.
17 Market Lane, Melbourne, flowerdrum.melbourne

Aru
Aru dials up its oyster offering by warming them and adding paperbark oil, finger lime, shallots and perilla.
268 Little Collins Street, Melbourne, aru.net.au

Pearl Diver
Choose from raw or cooked, dressed or natural, and even which region you prefer your oysters from at this temple to the bivalve. A daily deal (5pm-6pm) offers a tower of 18 mixed oysters with two glasses of sparkling for $100.
56 Little Bourke Street, Melbourne, pearldiver.com.au

Society
Akoya shows up two ways: on the seafood platter alongside tiny crab tarts and other treats, or riding shotgun with coral trout, one of the main courses.
80 Collins Street, Melbourne, societyrestaurant.com