[PETERHEAD, Scotland] "One, two, two. One, three, four. One, three, six," the auctioneer bellows in a rich Doric accent native to Aberdeenshire in north-east Scotland.

This is Europe's biggest wholesale market for freshly-landed fish, where the looming Scottish independence referendum on Sept 18 is putting many traders on edge.

More than 130,000 tonnes of white fish, herring, mackerel and shellfish pass every year through Peterhead, 254 km north-east of Edinburgh. The town's port authority is so confident about the future that it plans to build a bigger market hall to accommodate a higher volume of fish. But there is a cloud on the horizon.