Finfish cage culture in Asia: an overview of status, lessons learned and future developments

摘要

The paper provides an overview of cage culture in Asia, with an emphasis on farming of finfish in freshwater cages. Cage culture in all probability originated in Asia, with earliest records going back over 2000 years in China. "Traditional" systems, distinguished by reliance on natural construction materials such as wood and bamboo, collection of fish from the wild, and feeding on locally available resources, are still found in several countries in Asia. In the past few decades such traditional systems of holding have evolved into more "modern" cage farming, involving specially constructed cages, better designs and synthetic net materials, use of hatchery reared fry and fingerlings, various types of feeds, including formulated feeds and better organized management practices. Even though such modern systems are increasingly common, there is a diversity of cage farming systems found in Asia, covering a spectrum of traditional to modern systems, small to large-scale, with farming involving a very widevariety of species and environments, levels of input and risk. Small-scale farming enterprises still dominate the sector in many Asian countries though. Cage culture has expanded in Asia because of a number of advantages, including the fact that cages make use of existing water bodies, and no land is required for farming (although land may be required for access to water bodies where cages are located). In many Asian countries, major inputs required for cage farming - feed, seed, materials, suitable water bodies, as well as technical support and markets — are available. Cages also provide opportunities for non-land owning sectors of the community to start fish farming, important in countries where fisheries are in decline, capitalizing on skills andsupplementing income of fishers and people without easy access to land. In newly created water bodies, such as reservoirs, they have shown potential to provide an important means of fish production, and sometimes opportunities for alternative livelihoodsfor people displaced due to impounding. In economic terms, there may also be advantages over land-based farms, although capital costs of investment in cages and inputs (seed and feed) may be a constraint to involvement of poor people. Marketing and economic aspects are key sustainability issues. There are several examples in the region where cage farming was promoted without due attention to economics and marketing, leading to poor sustainability of projects. There are a number of disadvantages that need to be recognized as constraints to the development of cage farming. The key word is "vulnerability". Cages are "open systems", and therefore highly vulnerable to changes in the surrounding environment. They are vulnerable to water quality changes, forexample resulting from water quality degradation (that in some cases may be caused by the cage farms themselves, or external events such as red tides), fish disease, damage from storms (particularly in coastal waters) and security problems such as poaching. Environmental constraints are therefore also key issues in the success and failure of cage farming. The paper describes in detail the design and construction of cages, farming systems and practices, types of water bodies used for cage culture, majorconstraints, with an emphasis on environmental aspects, and provides recommendations concerning policy and legislation. Two detailed case studies involving common carp and tilapia farming from Indonesia and Malaysia, and one describing the recent history of river catfish farming in Viet Nam, are provided.