Cows have been overtaken by fish. For the first time in modern history, the world has been producing more farmed fish than farmed beef. But instead of being a boon for the environment, many fish farms are damaging it because of the types of fish they breed.

 

A report by the Earth Policy Institute in Washington DC has found that farmed fish production is rising rapidly, reaching a record 66 million tonnes in 2012. Cattle farm output, by contrast, has leveled off, with just 63 million tonnes of beef produced in the same year.

 

If current trends continue, humans are set to consume more farmed fish than wild-caught fish by 2015, says the Organisation for Economic Co-operation and Development.

 

Some farmed fish are good for the environment. Chinese aquaculture, which accounts for 62 per cent of the world's farmed fish, relies heavily on species such as silver carp. These can be grown on rice paddies and feed on grass, plankton and detritus. This relatively sustainable way of farming fish boosts rice yields and produces little pollution.

 

However, other popular farmed species such as salmon are carnivorous. They must be fed on smaller fish like anchovies, caught from the wild. As a result, salmon can only be farmed by further depleting wild fish stocks. "It would be preferable to shift the balance back in favor of farmed fish raised without feeds based on protein from other animals," the report concludes.