Enjoy the flathead fillets dished up last night? Chances are the "flathead" was an unrelated species, bottom-trawled in Argentinian waters.

Australia's lax labelling laws for seafood mean restaurants and retailers can withhold information on the origins and species of popular seafood, depriving consumers of the ability to make informed choices.

On Thursday, Greenpeace and the Australian Marine Conservation Society launched the Label My Fish campaign, demanding Australian laws match the European Union standards that require the origin, species and method used to catch or farm be declared on seafood labels.

"The Aussie 'flathead' we think we are eating may well be an imported, cheaper South American fish, of a completely different family," said David Ritter, chief executive of Greenpeace Australia. "But there is often no labelling on your pub or fast food menu, or packet of frozen 'flathead', to reveal the truth."

The Label My Fish alliance, backed by celebrity chefs, academics, and Taronga Zoo and Zoos Victoria, says clearer labelling will encourage the use of sustainable fishing methods, boost the local fishing industry and lift public health protections.

Greenpeace research shows basa, native to the Mekong Delta and not a member of the dory family, is often marketed as "pacific dory". Two-thirds of barramundi is imported from Asia.

Pregnant women and children under six are warned by health experts to limit their consumption of certain species, such as shark (sold as flake), catfish and orange roughy, because of mercury content.

"But the labelling laws make it impossible for pregnant women to follow the warnings and that's a big shock," said Mr Ritter.

Restaurant and Catering Australia opposes the calls, saying the industry will lose $300 million a year to comply with such laws. The "onerous" task will require updating menus, reconfiguring back-end systems and maintaining compliance.

Its chief executive John Hart said with 70 per cent of seafood coming from overseas through "fragmented", "irregular", and regularly disrupted supply chains, even suppliers will struggle to offer detailed information about the product.

"There's a long way to go before we're even half way close to being able to meet such labelling requirements at the back door of restaurants," he said. "Most of the suppliers don't have anywhere near that level of information. If we don't know, we can't put it on the menu."

Frank Camorra, executive chef of the hatted MoVida restaurants, changes his nuevo-Spanish menus daily and has thrown his support behind the campaign.

He says his suppliers, Joto in Sydney and Clamms Seafood in Melbourne, "know exactly who's caught the seafood, how it's been caught and where", allowing him to share information readily with patrons via menus and wait staff.

"It seems common sense to me. People want to know not only which state it comes from, but almost which regions," he said, referring to items such as surf clams, prawns and scallops.

Greenpeace says new labelling laws will also benefit local and overseas fishermen who have invested in fishing sustainably but struggle to compete with cheaper imports.

Louis Hatzimihalis, a fisherman from Port Phillip Bay in Victoria, has stopped catching arrow squid and scallops because of imports from South America and China. "We can't afford to catch it at that price. But you just can't compare the quality."

Consumer advocate Matthew Evans interviewed chefs, retailers, suppliers and fishermen here and abroad to examine the impact of weak labelling laws for a three-part series called What's the Catch?, to be screened on SBS from October 30.

"Some [fishing methods of] seafood we eat damage our marine environment, are produced by people under unfair conditions and may carry risks to our health," he said. "What we really need is to know just what's on our plates."

Chefs Peter Gilmore of three-hated Quay and Tom Kime of Fish & Co have also joined the demand for labelling reforms. Academics from the Australian National University, Sydney University and the University of NSW have also given their support.

A Senate inquiry into seafood labelling is underway and will deliver a report on December 4.