(De Nederlandse versie van dit artikel staat hier)

We call our planet “Earth” but really it’s more sea than earth. Biologists keep warning us that we are depleting our seas. The total number of marine animals caught in the wild is still rising, but we have already caught the most we will ever catch of some species – especially the tasty ones – and there are increasingly fewer of them. Besides, many other creatures are victims of our fishing too: bycatch, or animals like turtles and dolphins caught in the webs or lines left behind. Trawling nets sweep across the bottom of the sea like a saturation bombing, leaving a desert bereft of life.

In last week’s issue of Science, American ecologists stressed the urgency of intervention to avoid a “defaunation disaster”.

Nonetheless, if all humanity suddenly decided to stop eating wild fish tomorrow, we would face other problems. In 2012, fishermen all over the world caught 91.3 million tonnes of fish and other marine animals, according to the Food and Agriculture Organisation (FOA). If we were to replace that fish and those shrimps and molluscs, we would need to plough up vast tracts of natural areas for agriculture of for growing fodder for the animals we would eat instead of fish.

To protect nature, both on land and in the sea, we urgently need alternative ways for supplying protein to the global population. Consequently, the eyes of the world have turned to Asia, where industrial-scale fish farms are popping up at a fast rate. Of the 70 million tonnes of farmed aquatic creatures produced globally in 2012, 90 per cent came from Asia – half came from China. The shrimps, pangas fillets and tilapia in your freezer probably all came from an Asian aquafarm.

“How ethical and sustainable is it to eat it?” asks Patrik Henriksson at Leiden’s environmental institute, CML. In recent years, the Swede has done many calculations concerning the fish farms in an attempt to answer this question. The sums involved are called life-cycle analyses and eventually produce a “foot print”: the amount of land use, CO2 emitted, clean water used, etc. Recently, in the trade journal Aquaculture, Henriksson revealed the foot prints produced by various shrimp farms. “We always try to show several categories because it’s very easy to stare blindly at one factor and make a serious mistake. Take biofuels, for instance, which are better for the climate than mineral oil. However, rain forests are being cut down to make space for oil palm plantations, and food prices went up. We need to include all the effects in our calculations.”

Aquafarming is not without disadvantages either. “There have been some huge problems, especially back in the eighties and nineties. Use of antibiotics was rife, for one thing. Mangrove forests were destroyed to make room for farms and the farms allowed their waste water to leak into nearby coral reefs. The 2004 tsunami demonstrated the importance of mangroves as coastal protection and as breeding grounds for marine fish. Many countries now protect the mangroves more carefully and in many places the farms are now situated behind the mangrove forests.”

Another problem is feeding the fish. One of the most important sources is fish meal. Sea creatures we don’t like to eat are finely ground and used as feed. It is not very efficient, as Hendriksson reveals: “For example, the salmon farming breeding industry consumes more fish protein than it produces.”

However, he observes that the industry is improving in this respect too. “We must encourage good methods. Pangas and tilapia are omnivores and only need a very small percentage of fish meal in their food. The remainder of their diet consists of plants: soy, cassava, maize and rice bran – the brown stuff left after milling rice. If you can use that kind of waste, the kind that people don’t, or hardly, eat, you can produce more food.”

In a recent article in Science, Henriksson and his colleagues from various countries assessed the Chinese demand for fish meal. Figures are hard to obtain, but the Chinese demand appears to be huge. The best estimation Henriksson and his colleagues can make is that aquafarming in China requires 1.4 million tonnes of fish meal annually – the equivalent of 6.7 tonnes of fish. A quarter of fish caught in the wild is used in fish meal factories.

This leaves plenty of room for improvement, not only by choosing fish that also eat plants, but also by processing the fish we eat more efficiently. “It’s too expensive to fillet fish in the West. Cod caught in the Atlantic is frozen on board and usually sent to China for filleting while the heads and other parts stay here. Only one third of a tilapia is fillet, the rest of the fish could ground to fish meal, which happens in some places, but not always very efficiently and not it’s not done everywhere yet. The whole industry should be encouraged to do it.”

The research says that any worries about weird diseases arising from cannibalism could be avoided by feeding shrimp meal to fish and fish meal to shrimps, while technical solutions have been found for the gradual accumulation of heavy metals and other toxins.

Though a vegetarian himself, Henriksson claims that nobody should feel guilty about eating farmed fish or shrimps. “It’s a good way of producing animal protein. Because they are cold-blooded, they need far less energy than mammals and their environmental impact is much lower. The fish are farmed in water so there is less competition for land use. And eating fish is quite healthy, which is another advantage. You often hear that aquafarming must be quite dirty because it’s in China, but those prejudices are not always founded. The process could be made a lot more sustainable, but in the meantime, the Chinese are feeding millions of people.”

Top three

The Asian aquaculture industry uses more than over a hundred kinds of freshwater fish, sixty saltwater species and an unknown quantity of molluscs and shellfish, although we eat little of them in the Netherlands, as we prefer:

Pangas

Not so very long ago, you could buy “cat fish” in Dutch supermarkets, but you don’t see that name any more. You can still get cat fish but now it’s called “pangasius” or “pangas”, which could designate any one of a number of related species.

However, Pangasius bocourti and Pangasiodon hypophthalmus are the most popular. An adult of the latter species can grow to be 130 centimetres in length and weigh as much as 44 kilograms. Most pangas comes from fish farms in South (East) Asia, where production increased twelvefold between 2008 and 2012.

Tilapia

A tasteless but firm-fleshed fish, which makes it very suitable for selling – covered in far too salty marinade – to people who don’t like cooking or fish.While there are dozens of tilapia species, the production of Oreochromis niloticus amounts t 3. 2 million tonnes, according to the Food and Agriculture Organisation (FAO). Its surname niloticus does indeed mean that the species originally hails from the Nile, but they are farmed practically everywhere nowadays. They do not require much in the way of water quality but it should be warm, 20 degrees in fact, which is why tilapia are farmed in power plants’ waste water in colder climes.

Penaeidae

A generic name for approximately twenty species of shrimp, of which the most well known (Penaeus monodon) are sold here as tiger prawns. 4 million tonnes of tiger prawns and a related species, P. vannamei (a.k.a.: whiteleg shrimp), are produced globally.

Compared to fish, shrimps and prawns need relatively large amounts of fish meal or fish oil in their diet, about a quarter of their total consumption.