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Aquaculture: (Not) Half the Fish We Eat

Editor's Note:
The Sea Around Us Project, a scientific collaboration between the University of British Columbia and the Pew Environment Group, was started in 1999 to ensure the social and economic benefits of sustainable fisheries, analyze fisheries impacts on marine ecosystems and devise policies that mitigate and reverse harmful trends. The Sea Around Us maintains global databases of catches, distribution of commercial marine species, fishing access agreements, ex-vessel prices, marine protected areas, global mariculture and other data —all available online to encourage collaboration. Further information is provided at www.seaaroundus.org.

The Sea Around Us Project provided key data and expertise on global fisheries and mariculture for the Ocean Health Index’s Food Provision goal.

Dr. Daniel Pauly

These days, anyone interested in ocean affairs will have heard the notion that “half of the fish we eat come from aquaculture.”

Aquaculture, it seems, will save us from ourselves, and save the oceans from our depredations. But is this notion valid? One might ask: is the growth of aquaculture really providing half of the fish we now eat? Also--can we really assume that aquaculture is going to provide us with enough fish to maintain present per capita consumption even while our population increases to 9 or 10 billion? And is it true that the growth of aquaculture lessens the pressure on wild fish stocks?

The United Nations Food and Agriculture Organization (FAO) provides the closest there is to a definition of aquaculture as:

“the farming of individually or corporately-owned aquatic organisms such as fish, molluscs, crustaceans, and aquatic plants with intervention in the rearing process so as to enhance production”  [1].

Aquaculture production has indeed increased rapidly – even exponentially -  in the last three to four decades, and by now, the joint production of  freshwater aquaculture, combined with the production from mariculture, the brackish and marine counterpart to freshwater aquaculture, does indeed represent about half of the nominal catch of the world marine and freshwater capture fisheries, as reported by FAO.

So at first glance, the notion that “half of the fish we eat come from aquaculture” appears sound. But let’s examine this assertion is some details.

Nearly two-thirds of aquaculture production originates in China, as freshwater fish with low trophic levels (especially carps) and mariculture production of bivalves (such as cockles). There are uncertainties over the accuracy of Chinese aquaculture statistics, and therefore the status of global aquaculture trends; thus, FAO [2] writes:

“There are continued indications that capture fisheries and aquaculture production statistics for China may be too high, as noted in previous issues of The State of World Fisheries and Aquaculture, and that this problem has existed since the early 1990s. Because of the importance of China and the uncertainty about its production statistics, as in previous issues of this report, China is generally discussed separately from the rest of the world.”

However, a recent study of mariculture production data [3], which analysed China (and other large countries) at the sub-national level failed to identify discrepancies between Chinese provincial and national data as submitted to FAO. So the problem lies elsewhere, with the averaging that is (implicitly) performed between China’s contribution of nearly 2/3 of global aquaculture production and the production of the rest by …the rest of the world. You get a number, obviously, but the question is then: who is the “we” in “half of the fish we eat come from aquaculture?" 

If for example you average the income of a multibillionaire and of a poor person, what you get as a mean is not a ‘middle class’ income, but that of another multibillionaire! This example is extreme, but perhaps suffices to highlight the problem resulting from postulating the existence of a world average person, with a consumption of aquaculture products at a rate intermediate between that of China and the rest of the globe.  

Since China produces two-thirds of the world's aquaculture and since most of it is eaten in China, the Chinese people have a higher per capita consumption than the rest of the world. Approximately 1 billion Chinese share two-thirds of the world’s production, and the other 6 billion share the remaining third.  It’s all good for global supply, but we can’t say that per capita consumption of aquaculture is equal all over the world.

This second issue pertains to the word ‘fish’ in the sentence “half of the fish we eat come from aquaculture.” There are two basic types of aquaculture, let’s call them A and B. Aquaculture A is devoted to the farming of bivalves such as oysters and mussels, or freshwater fish such as carp and tilapia. It relies on plants (plankton sometimes supplemented by agricultural by-products in the case of freshwater fish) to generate a net addition to the fish food supply available to consumers.  Moreover, because this type of aquaculture is based predominantly in developing countries (mainly China, but also for example in the Philippines and Bangladesh), it supplies cheap animal protein exactly in the places where it is needed.

In Timor-Leste, girls sell a batch of fish like this for one U.S. dollar.

Aquaculture B entails the farming of carnivorous fish such as salmon or sea bass, and increasingly, the fattening of wild tuna in captivity. Salmon, sea bass, or tuna, eat flesh--albeit fish flesh; in zoological terms, they are dragons feeding on the wolves and lions of the sea. When fed only vegetable matter, such as soy meal, salmon do not grow well, and end up looking and tasting like tofu. Unless substantially better plant-based substitutes are developed--and we don't know whether that will be possible--there is no point even trying to feed tuna anything but fish.

The more of Aquaculture B there is, the less cheap fish, such as sardines, herring, mackerel, and anchovies there will be for humans to buy and eat.  Farming carnivorous fish increases rather than reduces pressure on wild stocks.  It has led to massive imports by developed countries -- where this type of aquaculture predominates -- of fishmeal made from fish caught and ground up in developing countries. Aquaculture B is indeed ‘farming up the food web’[3,4,5], which supposed to compensate for widespread "fishing down."  

One reason why the aquaculture industry and its spokespeople can get away with this is that the public at large assumes that the operations in A and B are similar, and that both types add to the global fish and/or seafood supply.  In the case of Aquaculture B, it is not true that “aquaculture reduces the pressure on wild stocks.” The opposite is the case.  Indeed, there is a perverse, additional effect:  in order for aquaculture B to sell an increasing amount of products (since it must grow, like any other commercial enterprise), the firms must widen their customer base, which they do through advertising that emphasizes the desirability of seafood, not least because of its putative health benefits. This however, increases demand for all kinds of seafood, and not only that which is farmed.  Aquaculture, or at least Aquaculture B, cannot at present “reduce the pressure on wild stocks.” This is another false notion connected with aquaculture, at least in Western countries.  Only if Aquaculture B drastically reduced its reliance on wild fish could that be contemplated.

We looked at the words "we" and "fish" in the sentence “half of the fish we eat come from aquaculture.” Now, finally, we may look at the word "half," at the head of the sentence. The actual value of a fraction such as ½ is determined both by its numerator (aquaculture production) and its denominator (catch for human consumption from capture fisheries + aquaculture production). As it so happen, the nominal catch used by FAO strongly underestimates the actual catch of capture fisheries, by approximately by 30-50 % in developed countries [6], and 100 – 300 % in developing countries [7]. This is because it does not include by-catch and discards, illegal, unregulated or unreported catches (IUU), or, generally subsistence and recreational catches, which may be substantial in some places. Taking this into consideration, the ‘half’ is reduced to about 20% or less.

Thus, of the sentence “half of the fish we eat come from aquaculture” the words "half," "fish" and "aquaculture" are either misleading, or must be viewed with caution. There is thus no need to dwell on the many environmental, disease and associated problems with Aquaculture B to be weary of this form of intensive food production. It is a pity, however, that by association, Aquaculture B has tarnished Aquaculture A, which is a true solution to some of our food security problem. What's more, the misleading statement that we have dissected here could make producers more complacent than they should be about the contributions of Aquaculture B and less focused on replacing fishmeal with sustainable alternatives. Without that change, Aquaculture B will continue to be a drain on wild stocks.


[1] FAO. 2009. FAO Fisheries Glossary. url: www.fao.org/fi/glossary/default.asp. Accessed: April 28, 2009.

[2] FAO. 2009. The state of world fisheries and aquaculture 2008. Rome: FAO Fisheries and Aquaculture Department, 196 p.

[3] Campbell, B and D. Pauly.  2013. Mariculture: a global analysis of production trends since 1950. Marine Policy 39: 94-100.

[4] Stergiou, K.I., A.C. Tsikliras and D. Pauly. 2009. Farming up the Mediterranean food webs. Conservation Biology 23(1): 230-232.

[5] Pullin, R.S.V., R. Froese, and D. Pauly. 2007. Indicators for the sustainability of aquaculture. p. 53-72 In: T.M. Bert (ed.), Ecological and Genetic Implications of Aquaculture Activities. Kluwer Academic Publishers, Dordrecht, The Netherlands.

[6] Zeller, D., Rossing, P., Harper, S., Persson, L., Booth, S. and Pauly, D. 2011. The Baltic Sea: estimates of total fisheries removals 1950-2007. Fisheries Research 108: 356-363.

[7] Zeller, D., S. Booth, G. Davis and D. Pauly. 2007. Re-estimation of small-scale for U.S. flag-associated islands in the western Pacific: the last 50 years. U.S. Fisheries Bulletin 105: 266-277.