Tassal and Petuna Seafoods are both ASC-certified and Huon Aquaculture is in the process of winning the prized label, which is regarded as one of the most stringent assessments on world’s best practice fish farming.

ASC national representative Duncan Leadbitter, who was in the state on Friday, said there were 150 points of compliance for the certification under ​seven principles, covering key areas such as environmental standards, habitat protection and social policy.

The ​certification lasts for three years and each year there is an annual surveillance audit.

Mr Leadbitter said one of the key principles of ASC was a concept of “continuous improvement.”

“It is not designed to be a binary pass or fail; it is designed to look at how companies commit themselves to making improvements,” he said.

Environment Tasmania released an open letter signed by 17 state environmental groups, calling for an end of conflicts of interest with the ASC.

It said the World Wildlife Fund, a founder and council member of the ASC, received $250,000 annually from Tassal, which created questions over the certification’s independent process.

“Tassal has retained this so-called best-practice certification regardless of breaching key ASC standards on sustainability and fish welfare for three years now,” Environment Tasmania strategy director Laura Kelly said.

“The only way we can explain this is the large sums of money changing hands between Tassal, the ASC and WWF.

“The ASC needs to cut financial ties to the companies it oversees.”

But WWF's Australian fisheries and seafood manager, Jo-anne McCrea, denied there was a conflict of interest as certification assessments, approvals, and audits were done by third parties

She said the $250,000 annual payments to WWF were for technical support and to support conservation projects.

Ms McCrea said the partnership was developed between Tassal and WWF in 2012 after the organisation was looking for a body in the Tasmanian industry to “lead the way”.

“WWF work with some of the world’s biggest producers that have the potential to cause significant environmental impacts and help them transform to sustainable practices,” Ms McCrea said.

“We hope that encourages others in the industry to follow and that’s no truer anywhere else in the world as it is in Tasmania.”

Petuna Seafoods acting-chief executive David Wood said the company achieved ASC certification 12 months ago.

“The benefits to the business are two-fold: one is from a sales perspective but the real benefit is that it impacts the culture of the company and the way our workers perform,” he said.

He said 85 per cent of salmon sold in Tasmania was not branded, however, so most consumers did not know whose product they were buying.