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Pond culture in the Red River Delta, Vietnam.

Abstract
 The Red River Delta (RRD) in north Vietnam, one of the most densely populated areas in the world with over 1000 people per km2, has a traditional small-scale integrated farming system known locally as VAC in which a polyculture of carps is raised in household-level ponds in association with livestock and crops. VAC is an acronym for the Vietnamese words for garden (vuon), pond (ao) and livestock quarters (chuong). There are diverse linkages between VAC subsystems which vary with agroecological zone. The importance of VAC has long been recognized for household food security and increasingly as a source of income as the rice-based economy is diversified. Research with farmers has improved the efficiency of use of on-farm and locally available resources in VAC with extrapolated fish yields of 3-4 t ha-1 in the 700-1000 m2 ponds, giving cost:benefit ratios of 1:2.7-2.8.