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TROUT are troublesome for fish farmers because harvesting their eggs is laborious and expensive. So a team of European researchers has developed a hormone-laced food that makes the fish spawn predictably.

Trout commonly spawn over a two-month period, during which they must be inspected regularly to decide whether their eggs are ripe and can be manually harvested. But because farms can stock thousands of fish, the inspection process is laborious.

Now, however, researchers believe they can get around the problem by feeding trout microspheres laced with gonadotrophin-releasing hormone (GnRH), which encourages the fish to produce eggs. The hormone is combined…

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