Fish Populations Out of Their Depth

Nearly half of the fish that we eat today haven't been caught from seas, rivers or lakes but began life in a farm, just like the beef, pork and chicken that we eat, according to the latest report from the UN Food and Agriculture Organisation (FAO).

There has been a massive boom in the amount of fish that are farmed, a process known as aquaculture: in 2004 we were growing 45 million tonnes of fish compared to 60 million tonnes which were being taken from the wild.

With the number of people in the world climbing ever higher, there will be more and more demand for fish to eat, but the problem is that we are already maxing out the amount of fish we can catch from the sea - even with more fishing boats with bigger and better fishing gear we are still catching about the same about of fish from the seas that we have for the last few decades.

So, maybe the only way we're really going to be able to meet this increasing demand for fish is to grow them ourselves.

This week at the BA Festival of Science in Norwich I went to a session all about "Should we eat fish" - and it's unclear whether this increase in farmed fish is a good or a bad thing for the world.

On the negative side, there worries that farmed fish had spread diseases and parasites to wild fish, and that escapees from fish farms which can genetically contaminate the local wild gene pool. And some farms can generate lots of water pollution from leftover feed and excrement from the fish. And then there's a problem that many of the farmed fish are fed on other fish, which are still being caught from the seas.

But, on the positive side, farmed fish does help to feed people in the developing world and could provide a very important, more secure source of food. And there are some species that are becoming endangered in our seas that maybe we can grow and so leave alone the wild stocks.

And did you know that cod, that favourite ingredient for fish and chips and fish fingers, are now being sustainably grown for the first time in the Shetland Islands? It's early days, but if it takes off, this could help reduce pressure on those wild stocks: maybe one day the Japanese will be farming blue finned tuna for their sushi!