Tasmania's largest salmon producer has announced it will soon use natural pigment supplements in its fish feed, three days after a Four Corners report on the state's industry showed the use of a synthetic version to colour the flesh, but the company says the move has been considered "for some time".

A salmon pigment chart, as seen on the Four Corners Big Fish report. ( ABC Four Corners )

Tassal said it would use naturally derived astaxanthin in its fish feed, ending its use of a "nature-identical" synthetic version which is added to the farmed salmon's feed to colour the flesh from white or grey to the pink colour common in salmon which feed on krill and other foods containing naturally occurring astaxanthin.

The announcement came three days after ABC's Four Corners report on the Tasmanian salmon farming industry highlighted the use of synthetic astaxanthin in feed by salmon farming operations, including Tassal.

In a statement, Tassal CEO Mark Ryan said the company "had been investigating the viability of using a natural astaxanthin for some time".

"We started this work because of the growing consumer preference for natural and organic products," he said.

"Sourcing a sustainable and reliable source of natural astaxanthin has been a complex task, but we are confident that by 2017 the first diets containing natural astaxanthin will be delivered to our farms.

After being contacted by the ABC, Tassal's rival company Huon Aquaculture said they were "transitioning to a naturally sourced astaxanthin" as part of its new feed agreement with its major feed supplier.

"Whilst we would have preferred not to say anything until we were assured of reliable supply of 100 per cent of our salmon feed product containing the naturally sourced astaxanthin, we understand that the recent Four Corners story and Tassal's announcement today has increased interest in the use of astaxanthin," Peter Bender, managing director and CEO of Huon Aquaculture, said in a statement.

"I commend Tassal for their move to the naturally sourced product as we are and I don't think it matters who gets there first.

I think it is another example of our industry taking regular steps to improve and respond to consumer and community feedback."

Petuna, Tasmania's other major salmon farmer, declined to comment.

'Simply replicating' wild salmon diet

Mr Ryan said Tassal would "work through existing stocks" of feed which contain the synthetic version of astaxanthin, and "work with feed supplier Skretting to phase in the new natural stockfeed pigment over the next 12 months".

Four days before the ABC report aired, the Tasmanian Salmonid Growers Association (TSGA), which represents salmon growers throughout Tasmania, uploaded a page on their website titled "Why is salmon pink?"

"The pink colour of salmon flesh, wild or farmed, results from the retention of carotenoids in the fish flesh. Carotenoids are a naturally occurring group of pigments, imparting colour to the tissues of a variety of organisms. More than 600 naturally occurring carotenoids have been identified in plants and animals. They are responsible for the colours of many fungi, fruits (tomatoes, paprika, citrus fruits), flowers (marigold), insects (ladybirds), birds (flamingos), fish (salmon, goldfish) and they produce the colours of the autumn leaves."

In his statement, Mr Ryan said said "while the current synthetic astaxanthin was completely food safe, Tassal understood that the use of natural pigment for salmon was more attractive to consumers".

"Wild salmon are naturally pink from their diet and we are simply replicating a natural diet for our salmon."

Natural pigment will risk profits, expert says

An investment expert said Tassal had escaped shareholder wrath over being highlighted in the ABC report.

A move away from fish feed with artificial astaxanthin could prove costly, an expert has said. ( Supplied: TSGA )

Roger Montgomery from Montgomery Investment Management said Tassal would face more scrutiny if it chose to use naturally derived astaxanthin, because of the increased cost to do so.

"If the company decides to adopt a natural colouring process rather than the synthetic, it's likely that will be more expensive, that will affect margins," Mr Montgomery said on November 2.

"The majority of consumers are buying many, many other foods that are artificially flavoured and artificially coloured.

"The fact that salmon has a synthetic colouring is not going to move the dial all that much."

On Thursday night, Environment Tasmania issued a statement calling on Tassal to confirm the replacement pigment will not be genetically modified.

"We commend Tassal for responding to consumer concerns. Environment Tasmania would like further information on the source of this colouring, so that we can assure consumers that the astaxanthin companies will now use to colour the flesh of their salmon is not produced using genetic modification," Laura Kelly, strategy director at Environment Tasmania, said.