Cooke Inc. became a substantial shareholder in Tassal in late June, having acquired a 5.4 per cent stake in the company.

Tassal on June 28 said it had received a "non-binding, indicative, incomplete and conditional" proposal from Cooke Inc. to acquire all Tassal shares via a scheme of arrangement for $4.85 per share.

That followed confidential proposals to buy shares at $4.67 and then $4.80.

Shares traded between roughly $3.40 and $3.80 in the weeks leading up to the most recent proposal

Despite the price premium on offer, Tassal said its board had determined the proposal did not reflect the business' fundamental value and was not in shareholders' best interests.

"The company's board of directors believes Tassal has an attractive independent future and is well positioned to deliver growth in shareholder value," Tassal said.

The share price shot up as details of Cooke's stake and its takeover offer emerged.

It was at $4.85 early on Wednesday morning, having remained around that mark since late June, and was at $4.95 at the time of writing.

Cooke's stake in Tassal had grown to 10.49 per cent by Wednesday, with the previous week's acquisitions ranging between 500 shares for $2410 and 1.336 million shares for $6.48 million.

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It spent $16.67 million on Tassal shares between July 13 and Wednesday, having earlier built its holding through late June and early July.

"Cooke believes its proposed cash consideration of $4.85 per Tassal share is an attractive premium considering Tassal's salmon volumes have been maximised given restrictions on new marine farming leases," it said on June 27.

Tassal has told the market it is well placed to profit from its big capital spending program of recent years.

Cooke operates in North America, South America and Europe.

It has about 10,000 employees in 10 countries.

It said Tassal employed more than 1700 people in Tasmania and on the mainland.