(Adds dropped "billion" to headline)
* Bid upsets Marine Harvest's plans to buy up all of Cermaq
* Plans one off dividend to 43-54 crowns a share
OSLO, June 17 (Reuters) - Private equity firms Bain Capital and Altor offered $1.1 billion for salmon farmer Cermaq's fish feed arm on Monday, complicating Marine Harvest's plans to take over the whole firm in a $1.7 billion hostile bid.
Oslo-listed Cermaq said it considered the bid for EWOS, its biggest unit "sufficiently interesting" to initiate talks and planned a huge one-off payout to shareholders if the deal proceeds.
"Cermaq assesses this offer to be substantially higher than the implicit value of EWOS in the historical valuation of the Cermaq share as well as in the offer from Marine Harvest," it said in a statement.
Cermaq would use some of the money to pay down debt and also planned to pay out 4 to 5 billion crowns to shareholders, or between 43 and 54 crowns per share, it said. Marine Harvest itself had offered 107 crowns for all of Cermaq.
Salmon farmers have been among the hottest stocks recently as global demand is rising sharply at a time when supply growth is limited and Chile, a top global supplier, is facing renewed signs of disease.
The battle over Cermaq heated up last month when Marine Harvest, the world's biggest fish farmer, offered to buy the company but failed to convince the board, or the Norwegian government, which owns 43.5 percent of the firm.
Marine Harvest, controlled by shipping tycoon John Fredriksen, said it would push ahead with the deal anyway, saying it was willing to take as little as one third of the company and could even raise the offer if the government would agreed to the deal.
Cermaq shares have traded just above the offer price for the past several weeks and last closed at 109 crowns, indicating shareholders still expected a higher offer.
$1 = 5.8121 Norwegian krones Reporting by Balazs Koranyi; editing by Patrick Graham