Fish and crustaceans that are not weakened by poor environmental conditions, or by other causes, such as parasitic infestation, nutritional deficiency, handling stress, or chemical intoxication, are more resistant to bacterial infections. This is due to the presence of a large amount of bactericidal substances in the blood, which helps overcome infections. So, the best precaution against the occurrence of bacterial infections is to provide the fish with optimum environmental conditions, adequate amounts of the right kinds of food and avoidance of stress, including overcrowding. Vaccination/ immunization and genetic manipulation (i.e., the development of specific pathogen resistant fry) are also some ways of preventing bacterial diseases. The use of antibiotics should always be an option of the last resort.

Outbreaks of viral infections can cause massive mortalities among cultured fishes or shrimps. Water temperature and age of the fish or shrimps are significant factors that influence the development of viral infections. Most fish viral infections occur at low water temperatures, hence, very few viral infections among fishes in warm water culture systems are reported. In addition, most viral infections occur among fry or fingerlings often causing severe mortalities, while older fish or shrimp develop resistance or are hardly affected. Stress from handling, poor water quality, high stocking density and poor nutrition also affect the severity of viral infections. Finally, aquaculturists should beware in importing non-indigenous fish or shrimps into the country as these are potential carriers of viral pathogens.

Filipinos whose main daily diet consists of fish and rice, are highly dependent on the coastal resources. The development of coastal resources in the Philippines has been traditionally exploitative in nature. Government policies, which dictated development in both the uplands and coastal areas, have been based mainly on abundant available resources without due consideration for sustainability. In the 1950s, vast tracts of mangroves were awarded to concessionaires and logged over for firewood and tanbarks. Mangrove woods were the preferred fuel source in coastal villages and most bakeries because of its high heating value, but a greater volume was exported to Japan as firewood but reportedly became the source of rayon. In the 1960s, the government adopted a policy aimed at increasing fish production by converting large areas of mangroves into fishponds for the culture of milkfish (Chanos chanos) and shrimps. Such policy was promoted by a government program, which classified mangrove timberland for fishpond development and opened loan windows in most government banks to finance fishpond development. It was only towards the end of the 1970s when the government realized the fishery value of mangroves. A National Mangrove Committee was formed in the then Ministry of Natural Resources, and a Mangrove Forest Research Center was created under the Forest Research Institute of the Philippines. The former was charged with the formulation of policies/recommendations for the conservation and sustainable management of the remaining mangrove forests in the country, while the latter worked for the generation of technology for the rehabilitation, production and sustainable management of mangroves. Not surprisingly, this “decade of awakening” was also significantly marked with an alarming decline in fish catch. The government then opened loans to fisherfolk for the purchase of motorized boats and improved fishing gear. The program ended with most fishers unable to payback their loans as their fish harvests and income continued to decline. The 1980s and 1990s were marked with significant efforts to rehabilitate destroyed mangroves and related coastal resources. In 1981, small islands indented by mangroves containing an aggregate area of 4,326 hectares were declared Wilderness Areas under Presidential Proclamation No. 2151. Also in the same year, Presidential Proclamation No. 2152 was issued declaring the entire island of Palawan and some parcels of mangroves in the country containing an aggregate area of 74,267 hectares as Mangrove Swamp Forest Reserves. In 1987, the Mangrove Forest Research Center was expanded to become nationwide in scope under the Freshwater and Coastal Ecosystems Section of the Ecosystems Research and Development Service of every regional office of the present Department of Environment and Natural Resources. Not long after, the Coastal Environment Program (CEP) and the Coastal Resource Management Project (CRMP) were launched in the regional offices of DENR in 1993 and in 1996, respectively. These programs promote community-based approaches to coastal resource management, making direct stakeholders partners of government in the sustainable development and management of mangroves, seagrass beds, coral reefs, and other coastal resources.

Under the Memorandum of Understanding (MOU) between SEAFDEC (Southeast Asian Fisheries Development Center) and JIRCAS (Japan International Research Center for Agriculture Sciences) an agreement was forged to collaborate on a research study on the growth, prevention and control of diseases of aquaculture fishes. Several studies are now being conducted at SEAFDEC AQD in Iloilo, Philippines. Under the same project, JIRCAS also implemented a research study on sustainable aquaculture in Thailand, “Sustainable Production System of Aquatic Animals in Brackish Mangrove Areas.” Implemented from September 2003 to February 2004, the study aimed to determine the role of benthic organisms as food of marine resources, the shrimp farming areas and the number of shrimp farms. Using six shrimp ponds with an area of 40 m x 20 m where the potentials of closed and circulating systems to purify shrimp farm wastewater were compared. The shrimp culture in Thailand started in the mid 1970s and subsequently increased in mid 1980s with the intensification of production systems. The high inputs of intensification inversely resulted to the decrease of mangrove areas. In Samut Songharm Province which is situated in the Gulf of Thailand, mangrove areas decreased to almost 0 for the last 15-20 years (Fig. 1). Due to the concerted efforts of the residents in the community and in support of the Royal Princes of Thailand, mangrove tree planting was started in the coastal areas in 1999. Fig 1 shows the areas covered by mangroves in the Province of Samut Songharm that mark the decrease and increase of mangrove areas.

The history of brackishwater pond culture in the Philippines and elsewhere in Southeast Asia has been associated with mangrove loss because in earlier times, the larger society has viewed mangroves and other wetlands as wastelands to be developed. In a proactive move to address environmental concerns over shrimp aquaculture, the SEAFDEC Council in 1999 mandated the development of environment-friendly shrimp culture and the build-up of expertise in mangroves. This paper reviews the status of mangroves and their conversion to culture ponds in Southeast Asia, and the environmental impacts of aquaculture, aside from habitat loss. To improve the sustainability of brackishwater aquaculture, recommendations include an inventory of mangrove and pond culture areas in the region, zonation of mangrove areas within the context of integrated coastal zone management, aqua-silviculture and environmentfriendly aquaculture, rehabilitation of degraded mangroves, and enforcement of existing laws including the buffer zone/mangrove greenbelt requirement.