As we have seen, the continued growth in production of aquatic organisms since the mid-1990s is due to aquaculture. Figure 3.1 shows the development of aquaculture production since 1970. The product mix of aquaculture is quite different, however, from capture fisheries. Fish, in the strict sense of the word, is barely one-half of the biomass produced by aquaculture (47 per cent in 2018). The largest category by weight is freshwater fish (40 per cent in 2018). Aquatic plants, mostly seaweed but also some microalgae, are the second largest category by weight: almost 30 per cent of the total production in 2018. Molluscs – that is, shellfish of various kinds (mussels, oysters, scallops, etc.) – rank as third, with 15 per cent in 2018. Then there are crustaceans, mainly shrimps, prawns, crawfish and crabs (8 per cent in 2018); diadromous fish, which include salmon (about 5 per cent in 2018); and marine fish (less than 3 per cent in 2018). In the capture fisheries (in a wide sense of the word), marine fish account for more than 70 per cent, freshwater fish for 11 per cent and aquatic plants for less than 1 per cent (numbers from 2018).

A rather different picture emerges if we look at value instead of quantity (Figure 3.2). Freshwater fish, crustaceans, molluscs and diadromous fish all have a higher value than aquatic plants, which have low value per unit weight; in 2018 they accounted for almost 30 per cent by weight but only 5 per cent by value, about the same as marine fish.

What are the species making up these broad categories? This is shown in Figure 3.3. Almost all cultivation of aquatic plants (not shown in the figure) takes place in four Asian countries: China, Indonesia, the Philippines and South Korea. Most of this is brown and red seaweed. Some is used for direct human consumption while the rest is a source of carrageenan, used by the food industry as thickener and stabilizer. Freshwater fish consist of carps, tilapias and miscellaneous fish; the last category includes catfish, which some developing countries (Vietnam, for example) export to Europe and the United States. Catfish are also cultivated in the southern states of the United States.