28 JUNE 2013 • WORLD AQUACULTURE • WWW.WAS.ORG Sidebar 1: NATURALFOOD Natural food in greenwater pond aquaculture and polyculture is in fact cultured food. The ponds are prepared, filled with water, fertilized, stocked with young planktivorous fish and shrimp, water quality is managed and fish are eventually harvested by farmers. If this is natural, then growing tomatoes is also natural. Sidebar 2: GREENWATER Greenwater microalgae are cultured in water impoundments that are often fertilized with wastes (manure, night soil and agriculture waste) plus supplementary feeds. Bivalve mariculture consumes green water that develops naturally in coastal water (which is often enriched by nutrients from anthropogenic sources). The development of chlorophyll-rich microalgae gives water a green color. The precise species composition in green water changes in place and time and is not sufficiently defined, as opposed to the high degree of control of the cultured organisms necessary in mass monoculture (Benemann 1992, Moriarty 1997). Typical greenwater studies document species from most major algal classes (e.g., Chlorophyceae, Cyanophyceae, Bacillariophyceae, Euglenophyceae, Cryptophyceae, Dinophyceae, Prasinophyceae, Prymnesiophyceae, and Raphidiophyceae- Cremen et al 2007). Green water also contains bacteria, fungi, phytoplanktivorous/bacteriovorous protozoa, small zooplankton, larvae etc. The greenwater aquaculture farms around the world that culture fish in fertilized ponds and other water impoundments (Schroeder et al. 1990, Pekar and Olah 1992) grow hundreds of million t of microalgae. This very low-cost algal biomass is evidently useful (in composition and concentration) for the feeding of millions t fish and shrimp. Moreover, greenwater aquaculture can be profitable when growing even the cheapest of fish. In fact, extensive culture costs less than more intensive forms of culture. Sidebar 3: POLYCULTURE Polyculture in aquaculture is the association of fish species with different food habits for the effective use of available fish foods in the pond and where wastes produced by one species may be inputs for other species (Milstein 2005). In a more comprehensive way polyculture may also refer to aquaculture integrated with other agricultural activities, where wastes produced by one activity may be inputs for another activity. Polyculture is the main fish culture system in Asia, the continent generating over 90 percent of the world aquaculture production. Traditional greenwater aquaculture systems that involve the integrated polyculture of mostly carps and more recently tilapias, are widespread in Asian countries (Edwards 2004), as well as in East Europe and the Middle East (Billard 1980). In the Asian practice, four or more of the following are often raised together: silver carp Hypophthalmichthys molitrix (a phytoplankton filter feeder), grass carp Ctenopharyngodon idella (a macrophyte feeder), bighead carp Hypophthalmichthys nobilis (a zooplanktivore), common carp Cyprinus carpio (a bottom feeder-omnivore), mud carp Cirrhina molitorella (a bottom feeding detritivore), tilapia, mullets, etc. The traditional Chinese system of carp polyculture has several on-farm linkages. Fertilizers include human manure or nightsoil for crops and pond; livestock manure, mainly pig, for crops and pond; vegetation or green manure for crops and pond; and pond mud for crops. Wild grass from around the farm and waste from vegetables grown for humans and pigs provide supplementary feed for the fish. Similar traditional integrated systems occur in other parts of Asia and the Indo-Pacific region, especially in West Java, Indonesia and the Red River Delta, Vietnam (Edwards 2004), and in Europe. In the main aquaculture nations there, carp polyculture is prevalent and over two-thirds of fish production depends on greenwater plankton (Adámek et al. 2012). TABLE 1. Production of the top planktivorous food fish in aquaculture in 2010 (FAO 2012) and the greenwater microalgae that feed them (million tons live weight/y). Species Production Plankton Fed Microalgae Consumption (%) Phytoplanktivory Zooplanktivory Total Silver carp 4.1 100 29 20 49 Bighead carp 2.6 100 10 64 74 Gibelion catla 3.9 100 15 96 111 Rohu carp 1.2 100 5 29 34 Nile tilapia 2.5 17 3 19 22 TOTAL 14.3 62 228 290
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