26 JUNE 2013 • WORLD AQUACULTURE • WWW.WAS.ORG Greenwater Aquaculture: the Largest Aquaculture Sector in the World Amir Neori Over half of global aquaculture production of 80 million t (all values are in live weight, unless specified otherwise) in 2010, as reported by the Food and Agriculture Organization of the United Nations (FAO) — Fisheries and Aquaculture Department, was non-fed organisms (FAO 2012). A similar fraction has been estimated for Chinese aquaculture (Tacon et al. 2011). Non-fed organisms feed on natural foods (see sidebar, page 30) and receive no aquafeeds (NACA 1989, Xie 1999). Non-fed production included 20 million t of aquatic plants (seaweeds), 14 million t of bivalve mollusks and 7 million t of planktivorous carps. About 10 million t of additional fish production was based on feed added only as a supplement (i.e. natural food and aquafeed in different proportions) (Rahman et al. 2008, 2010, FAO 2012; Table 1). Shrimp (5 million t) often consume natural food, most of it algae, as a major fraction of their diet, even when aquafeed is available (Bombeo Tuburan et al. 1993, Moriarty 1997, Tacon et al. 2002, Amaya et al. 2007, Tacon and Lemos 2013). Macroalgae are photosynthetic organisms that use sunlight and inorganic nutrients present naturally in coastal marine and brackish waters. Marine bivalves eat natural plankton, mainly microalgae. Both of these extractive species groups are produced in huge coastal farms, mainly in China (Fig. 1), but also in Korea, Japan, other Indo-Pacific nations and Chile. The natural food of planktivorous fish species is the plankton in green water (see sidebar, page 30). Greenwater microalgae, which sustains perhaps half of the world’s production of fish, shrimp and mollusks, are not merely natural food but a production sector, in fact the largest one, in aquaculture. Why is Greenwater Polyculture so Widespread? Greenwater plankton (Fig. 2) feeds fish, shrimp and shellfish in the world’s most widespread and generally sustainable aquaculture approach, polyculture (see sidebar, page 30). The profitability of polyculture farms is a natural outcome of the low cost of growing greenwater plankton and the additional value of environmental biomitigation services that the polyculture ecosystem provides to the farm (NACA 1989, Edwards 2003, 2004). These environmental biomitigation services can be as valuable to the farm as revenues from fish sales (Pillay and Kutty 2005). Thus, the costly waste treatment in industrial monoculture of fed fish, such as salmon, seabass and more recently tuna, is replaced in greenwater polyculture by extractive waste recycling, which is integral to the production process and generates income. This is how polyculture produces cheap (~US$1/kg) fish. The populations of different categories of plankton and fish in a polyculture pond are fine-tuned to complement each other with respect to feeding. Balanced feeding by planktivores of different plankton categories, controlled waste loading and pond water exchange are used to manage greenwater polyculture production. In extensive and semiintensive polyculture systems, certain combinations of ecologically different species at adequate densities use available resources efficiently, maximize the synergistic fish-fish and fish-environment relationships and minimize the antagonistic ones. Synergistic interactions among fish species are based on two interrelated processes: increased food resources and improved environmental conditions (Milstein 1992). In coastal seawater bivalve culture, the main marine greenwater aquaculture, the main management tool is selection of farm location. A suitable plankton-rich current and the proper choice of technology, placement and density determine the supply of plankton and oxygen to bivalves and the dispersal of wastes. Climate, local species, resources, regional traditions and markets influence the combinations of cultured species that are practiced in fish polyculture and bivalve culture systems. Types and Production of Algae that Form Green Water Algae are primary producers of organic matter from sunlight. Like other photosynthetic organisms, algae remove carbon dioxide from the atmosphere, produce oxygen as a byproduct and use nutrients to grow and produce algal biomass. Algae, most of them microscopic, supply about half of the oxygen in the atmosphere, do half of the global CO2 uptake, and are daily on the tables of millions of people in China, Japan and Korea in the form of fish produced in greenwater aquaculture. Recently algae have received much interest and have attracted large R&D resources because of their potential productivity and the high content of oil in some species (Chisti 2007, Huntley and Redalje 2007). Scientists believe that most of the oil pumped out of the ground comes from algae that lived millions of years ago. Algae are a good source of oil, but perhaps more crucially, algae are an excellent source of food, produce many useful biochemicals and effectively filter nutrients. The modern algae industry is diverse. Among the macroalgae, Greenwater plankton feeds fish, shrimp and shellfish in the world’s most widespread and generally sustainable aquaculture approach, polyculture. The rising global demand for fish protein can be satisfied sustainably and cheaply without further taxing the shrinking supply of fresh water and arable land by improving traditional greenwater aquaculture.
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