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Top fish farmer Mowi's Q1 earnings lag forecast

* Preliminary Q1 EBIT 194 mln euros vs poll 199 mln

* Output 104,000 tonnes vs forecast 102,000

* Norway unit's earnings margin lower than expected (Adds margins, background, bullets)

By Terje Solsvik

OSLO, April 15 (Reuters) - Mowi, the world's largest salmon farmer, reported a smaller-than-expected rise in first-quarter earnings on Monday as margins at its largest unit missed forecasts.

The firm's preliminary operational earnings before interest and tax rose 23 percent year-on-year to 194 million euros ($219.4 million) for the January-March quarter, while analysts in a Reuters poll on average predicted 199 million euros.

Formerly known as Marine Harvest, Mowi is controlled by Norwegian-born billionaire John Fredriksen, who also holds stakes in shipping and oil service firms Frontline, Golden Ocean and Seadrill among others.

Mowi's salmon output stood at 104,000 tonnes in the quarter, beating its own estimate, as well as that of analysts, which had both been for an output of 102,000 tonnes.

More than half its output, or 56,000 tonnes, came from the company's Norwegian unit, which recorded an earnings margin of 2.05 euros per kilo, lagging the 2.28 euros expected by analysts.

Mowi did not say why production had been higher than its own forecast, or why the margin in Norway was lower. A full earnings report is due on May 7.

While demand for farmed salmon has risen in recent years, global output has been largely stagnant as some producers struggled to contain outbreaks of disease and parasites, resulting in higher prices.

Mowi's Scottish and Irish units saw higher earnings margins than analysts had expected, but operations in Canada and the Faroe Islands lagged. In Chile, margins were in line with forecasts, the report showed.

Mowi's shares have risen 6.6 percent in the last 12 months to a close on Friday of 186.6 Norwegian crowns, making it the country's sixth-largest listed firm with a market value of 96.3 billion crowns ($11.35 billion).

Among firms that do not have the Norwegian government as the largest shareholder, Mowi's size is exceeded only by oil firm Aker BP. ($1 = 0.8842 euros) ($1 = 8.4869 Norwegian crowns) (Editing by Shreejay Sinha)