A review of cage aquaculture: Asia (excluding China)

Cage farming in Asia is practiced in fresh, brackish and inshore coastal waters. Freshwater cage farming is a very old tradition that is thought to have originated in some of the Mekong Basin countries. It currently occurs in all freshwater habitats and is extremely diverse in nature, varying in cage design, intensity of practice, husbandry methods and the species farmed. In general, freshwater cage farming is practiced on a small scale, but in some instances clustering of cage operations can contribute a significant level of production, as in the case of pangasiid catfish culture in the Mekong Delta and the combination of common carp (Cyprinus carpio carpio) and tilapia (Oreochromis spp.) farming in some Indonesian reservoirs. Overall, although clear-cut statistics are not available, cage farming is thought to be the most predominant form of freshwater aquaculture in Asia. In this paper, freshwater cage farming is only briefly considered; it has recently been reviewed by the authors (see Phillips and De Silva, 2006). Cage farming in brackish and inshore waters in Asia is relatively recent, being started in Japan. It is estimated that over 95 percent of marine finfish aquaculture is in cages. Open sea-cage farming in Asia is not common. Marine and brackishwater cage farming in Asia is also diverse, with a variety of species being cultured at varying intensities. In most nations the individual operations are not large, and often a clustering of farming activities is seen. This clustering is primarily a result of the limited site availability in coastal waters. Cage farming is most dominant in East and Southeast Asia, but not in South Asian nations. The main species farmed in brackishwaters are the barramundi or Asian seabass (Lates calcarifer) and the milkfish (Chanos chanos). Almost all cage farming of these species is based on hatchery-produced fry and the use of pelleted feed. In inshore marine cage farming, apart from traditionally farmed species such as amberjacks (Seriola spp.) and snappers (Lutjanus spp.), in Southeast Asia the cage farming of groupers (Epinephalus spp.) and cobia (Rachycentron canadum) is gaining ground, the former particularly to cater to the live-fish restaurant trade. Some cage farming in Asia is still dependent on wild-caught seed stock, particularly for grouper species. One of the main constraints to further expansion of marine-cage farming in inshore areas is the extensive dependence on trash fish, directly or indirectly, as a main feed ingredient. In the synthesis, a number of factors that would impact on the“way foreward” in cage aquaculture in Asia is dealt with. Overall, the future prospects for all forms of cage farming look relatively bright for Asia. However, it is suggested that the large-scale, capital-intensive, vertically integrated marine cage-farming practices seen in northern Europe (e.g. Norway) and South America (e.g. Chile) are unlikely to occur in Asia. Instead of large-scale farms, clusters of small farms generating synergies, acting in unison and thereby attaining a high level of efficacy are likely to be the norm, well into the foreseeable future. Off-shore cage farming is unlikely to become widespread in Asia, as its development is likely to be hampered by availability of capital and the hydrography of the surrounding seas, which does not allow the technology available elsewhere to be easily transferred. Despite these limitations and constraints, cage farming in Asia will continue to contribute significantly to global aquaculture production and Asia will also continue to lead the world in total produc-