What do you do as the owner of a sushi bar when you realise that worldwide fish stocks are in crisis? I was presented with this problem when one day in 1998 I walked into my restaurant, Moshi Moshi to find that there was no bluefin tuna on the belt because it had become so scarce it was on the road to extinction.

After much soul searching, and many discussions with Greenpeace and WWF, I embarked on a strategy that would make Moshi Moshi's fish procurement as sustainable as possible. The first thing I did was to take blue fin tuna off the menu. The second thing I did was to go down to Cornwall to speak to the local fishermen.

What I came away with was a deal: Moshi Moshi would buy the fish directly from the boats, offering a higher price than the middlemen, if the fishermen guaranteed to use the most sustainable fishing practices.

Back in 1998, when I opened the Duke of Cambridge, I was acutely aware of the impact the fishing industry was having on marine life. Clearly we needed a policy that was attempting to demonstrate that you could source fish in a way that was sustainable. With guidance from the Marine Conservation Society we created the first fish purchasing policy for restaurants that the MCS was willing to put public approval to.

Offering fish that is supporting an industry that is contributing to environmental stability rather plundering our oceans also happens to be excellent marketing! Lets not be shy about it, marketing good news is crucial, it spreads positive change.

Tom Aikens has been an established force on the British cuisine scene since he launched his first, eponymous restaurant in 2003. Only a year later Tom Aikens received its first Michelin star. The restaurant went on to receive a host of prestigious awards including three stars in the Egon Ronay guide. In November 2006 he opened his second site, Tom's Kitchen, followed in February 2008 by Tom's Place, a fish and chip shop with a focus on sustainability.

Fish is a legitimate part of our diet – indeed, many argue that it was the nutritional value of fish that kick-started the evolution of human intelligence. Now we have to apply that intelligence to managing our fish stocks for future generations. A fish shopper who cares about that will go out of their way to find fish from a sustainable source. That generally means knowing where it comes from, and how it was caught.