A rival to the Bluff oyster being farmed in the Marlborough Sounds is proving popular but the Bluff industry says it is no real threat to its iconic product.

The harvest of the Tio Point oyster is beginning this week for supply to local markets, while exports to the likes of Singapore and Hong Kong are being lined up by marine farmer Bruce Hearn.

Mr Hearn said his Tio Point oysters, although "basically the same product" as the Bluff oyster, had a point of difference in that they were being supplied in the shell, still alive.

Invercargill Mayor Tim Shadbolt had already warned against using the Bluff name to market their oysters "or he would come down on me like a tonne of bricks", Mr Hearn said.

"They're touchy about it, and who can blame them? They have had the market to themselves pretty much for a long time. And they suddenly see an interloper coming in and selling pretty much what they are harvesting.

"You have got people like their enterprise board saying 'no one can grow anything as good as a Bluff oyster'. But until they try them, how would they know?"

Graeme Wright, of the Bluff Oyster Management Company, said he had not tried the Tio Point oysters himself, but had heard from others that they were of a different flavour and texture.

"I don't see them as a threat at all, really. I see it as quite complementary if someone is putting a good product out. It will never be a Bluff oyster as such ... it is a farmed oyster."

The Bluff oyster harvested from its natural environment held a special attraction, Mr Wright said.

Mr Hearn said his company was trying to keep away from the traditional Bluff oyster markets.

"We'll have an effect around the edges by supplying some of the top restaurants which they may have supplied in the past. But mostly their market seems to be fish and chip shops and supermarkets and those people."

Leading chef Simon Gault has served both oysters in his restaurant and says they compare well. Some people preferred the farmed oyster over the iconic brand, and many could not tell the difference, he said.

Asked if the Bluff oyster industry should feel threatened, Mr Gault said: "People are always going to go for the Bluff oyster. They can relax."