* 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