Raising salmon in large farms on Scotland’s west coast is a multi-million pound industry that means everyone in the UK can enjoy salmon at a reasonable price. However, it has its problems. In just 45 years, the amount of farmed salmon reared in Scottish waters alone has risen from zero to around 150,000 tonnes and with this increased number of fish goes an enormous rise in the numbers of fish lice. Salmon are reared in cages in sea lochs. Thousands of fish grow and fatten in these inshore waters. No surprise, perhaps that they can fall prey to parasites – among them, the sea louse. Sea lice can latch on to salmon, eat their skin and blood, and cause infections. Anglers and conservation groups highlight the deadly menace these sea lice can pose to wild salmon stocks as they move to and from their spawning grounds. Sea lice are tough, and they’ve been resistant to many of the new treatments devised to defeat them. Scientists around the world have developed environmentally-friendly disinfectants, in-feed treatments, growth regulators, bath treatments, and research is well underway on possible vaccines. But none, so far, has been perfect. “We were concerned that they might not adapt to a sea lice diet, but we found that when they have a choice, they prefer the sea lice every time” said Alastair Barge from Otter Ferry Seafish. On the shores of Loch Fyne, a natural approach is being pioneered. The long sheds of Otter Ferry Seafish contain dozens of large green fish tanks, each bathed in electric light. The scene is rather like any other breeding operation, but on an enormous scale. In each tank, there’s a shoal of Ballan Wrasse – some so small, they’re almost transparent. The two year olds are golden-red and about the size of a goldfish and will be used as cleaners. The director of Otter Ferry Seafish, Alastair Barge, has been rearing Ballan wrasse on a commercial scale for four years now. It is a complex process – the water temperature, artificial weed, feed and light levels all have to be right. But he has worked it out, and he now has 50,000 of the fish maturing. He said: “It is quite an old idea. At the beginning of salmon farming, people seemed to realise that wrasse were a potential cleaner fish. But they are quite tricky to rear, so that’s why the idea went on the back-burner at that stage.… More:
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