Worth the effort
vital that they are given the right nutrients and stable conditions in order to get them produc- ing healthy eggs year after year. ‘Broodstock nutrition is where it starts’, says Barge. ‘If we don’t get that right there’s no hope later on. We feed them once a day on a fi sh ‘sausage’ made from a Biomar premix, and extra attractants and vitamins.’ They also grow live feed – artemia, a microalgae, on site. Spawning occurs in February, and is encouraged by chilling the water to around fi ve degrees – two degrees below ambient. The females are then stripped and the males ‘squeezed’, and the eggs are then transferred to the hatchery. The initial hatchery stage is the most crucial in the whole halibut farming process. ‘The eggs are in-
cubated for two months’, explains Barge. ‘That is why halibut is so diffi cult; in every other species the larval stage is only a few days before they begin to feed, it’s 40 days for halibut.’ ‘And not only do we have to
protect the larvae for forty days, we have to do it in saltwater, which is a lot more diffi cult than freshwater. As such the water is kept as stable as possible, with fi ltering, UV fi ltering and ozonisa- tion. With halibut, water stability is the key, so running a marine hatchery for 365 days a year is a real challenge, he continues. ‘A slight temperature fl uctuation in the yolk sac, for example, would deform the fi sh. It’s a real engi- neering challenge, so we have back up systems and alarms.’
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Around 100,000 juveniles are
produced, which are then kept in nursery ranks – some at Otter Ferry and some on Gigha – until they are around 100g, when they are transferred to the large tanks on Gigha. It takes about a year for the juvenile halibut to reach 100g. ‘Gigha is unique, because the
only place in Britain that has less rise and fall than Gigha Sound is somewhere on the Norfolk Broads’, explains site manager Rob Wilkieson, a native of Gigha who’s worked at the farm for eight and a half years. ‘The rise between high and low tide is less than a metre, which allows us to have a fl ow-through system straight from the sea with no pipes; as such our pumps are always in the water.’ These pumps transfer seawa-
Previous page: Alastair Barge (right) and Rob Wilkieson.
Clockwise from top left: Automated feeders in the nursery tanks; juvenile halibut; checking the water; the production of artemia; counting the juveniles; pumping water into the tanks on Gigha
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