Operational earnings before tax and interest were around £6.6 million in the fourth quarter of last year, compared with £44.3m a year earlier, way below analysts' expectations of £18m.
The Norwegian group had warned in October about the possible scale of the earnings slide, after reporting third quarter earnings down from £46m to £7m. It has forecast a 10% fall in volumes in 2013, but says it expects prices to rise to offset the decline.
The company, controlled by shipping tycoon John Fredriksen, has also said it is ready to take advantage of financial difficulties its rivals are likely to face at current salmon price levels.
Its Scottish facilities include four freshwater loch sites, five hatcheries and 25 sea farms, and it supports over 450 jobs.
Marine Harvest said its deal to buy Polish smoked salmon specialist Morpol was now under investigation by the competition authorities, and pending its consolidation into group accounts there would be a temporary easing of the group's banking covenant.
Its net debt at the year end was just less than £600m. The deal increases Marine Harvest's share of Scottish salmon production from 23% to 36%.
In the last quarter, Scottish output fell to 7000 tonnes, partly due to biological issues, behind the 11,000 produced in both Chile and Canada, and the 70,000 in Norway. Its Scottish arm was highlighted as its best-performing in 2011, with high production of more than 60,000 tonnes, and the group last year announced a five-year £80m investment programme in Scotland.
Marine Harvest's total volume in the final quarter was 103,000 tonnes of fish compared to its guidance for 101,000 tonnes.
"The result from Norway was positively impacted by the strongly improved market conditions from the end of the fourth quarter, which has continued into 2013," the group said.
Profitability, as measured in earnings per kilogramme through the value chain, was highest in Norway, followed by Scotland, Canada and Chile. Scotland is the largest producer of farmed salmon in the EU and third-largest globally.
The results from Chile and Canada were impacted by the continued very weak market conditions in the Americas, while Chile also suffered a listeria finding at the smoked salmon producer Delifish.
Associated costs including those of product recall pushed the group to a £2.75m loss in the quarter.