Tilapia–shrimp polyculture has played an important role in current efforts to control luminous bacterial disease caused by Vibrio harveyi. At present, green water technology is most extensively used by shrimp farmers in Negros Island in the central Philippines. While the contribution of tilapia as a biomanipulator is highlighted in the literature, the mechanism of action is not well understood. Data were gathered from shrimp ponds practicing two production systems: (a) green water system (probiotics + tilapia) and (b) closed/semiclosed system (probiotics alone). There was no difference between luminous Vibrio count (P < 0.05) in both systems, and water quality was found to be similar (P < 0.05). Because the green water system uses a bigger reservoir to raise the tilapia biomass, the net shrimp production was lower. In terms of direct cost of production, however, the green water system was 10–15% lower than the closed/semiclosed system because of significantly less aeration required. The polyculture maintained a more stable plankton environment during the early months of culture, which increased survival of shrimps. Various pathways are presented for the control of luminous bacterial growth in polyculture ponds: (a) fish feeding on organic wastes and conversion to feces; (b) selective fish foraging to increase the dominance of beneficial phytoplankton; (c) bioturbation of pond sediments; and (d) release in the water column of antimicrobials, fungi, or competing bacteria from the skin and gut mucus of tilapia.

In the Philippines, conflicts between fishing, aquaculture, tourism and other uses of the coastal waters are common because they are not clearly integrated into the management of the coastal zone. Resource use allocation then remains a challenging task for decision makers. Development activities that proceed without proper planning lead to more resource use conflicts and environmental degradation. This chapter presents the findings of a study to identify a strategy for incorporating aquaculture into coastal planning to reduce conflicts in the use of the coastal and river waters of Dagupan City, Philippines. Recommendations to improve coastal planning requirements are discussed. Based on environmental, social, economic and institutional considerations, the river system was subdivided into ten management zones. The zones were further reclassified into priority use zones as 'regulated zone' (Zone 1), 'mariculture and fishing priority zone' (Zones 2-7), 'non-fishery zone' (Zone 8) and 'fishpond priority zone' (Zones 9 and 10). Since unregulated fishpen development was a major concern of the local government, fishpen size and layout were standardized. The output of this study forms part of the legislation, Dagupan City Coastal Fisheries Resources Management Ordinance of Year 2003, Executive Order No 71, Series of 2003. It is intended to promote sustainable aquaculture development, generate livelihood and revenues, institutionalize the production and marketing of milkfish for the domestic and export markets and rationalize the use of coastal resources to ensure social equity and long-term environmental stability.