When Storm Amy battered the Scottish Highlands in early October, it tore through a salmon farm’s sea pens, releasing around 75,000 fish into open water in Loch Linnhe. The scale of the escape is alarming. It comes at a time when wild Atlantic salmon – already classified as “endangered” in Great Britain – are in decline.

For an animal so central to the UK’s ecology, culture and economy, the incident has serious implications.

At first glance, it might sound like a rare bit of good news: thousands of fish freed from captivity, perhaps even helping to bolster wild populations. But the reality is far less heartwarming.

These fish are not wild salmon in any meaningful sense. They are highly domesticated animals, selectively bred over decades for traits that make them profitable in captivity but poorly equipped for survival in the wild.

Aquaculture – the farming of fish and other aquatic species – has become one of the fastest-growing forms of food production in the world. The most valuable of all farmed marine species is the Atlantic salmon, which accounted for 18% of global marine aquaculture production value in 2022. The UK is the third largest producer, with almost all production centred around Scotland’s coast.

Modern salmon farming typically involves rearing young fish in........

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