Aquaculture may have originated at least twice in separate geographical areas, in North Africa and in China. There is considerable documentary evidence of long and continuous evolution of inland aquaculture in China. Polyculture of common carp and Chinese carps in ponds involving fertilisation and feeding is centuries-old. China introduced fish culture to Japan. There is also evidence of polyculture of major carps without use of pond nutritional inputs in India, dating back 1,000 years.
Inland aquaculture in the rest of the world, including most of Asia, is relatively recent. In most Asian countries aquaculture is only 20-50 years old and developed significantly only over the last 10-30 years (Pillay, 1979). This is probably because the supply of wild fish could satisfy the needs of fairly low human population densities in comparison to those of today. Aquaculture appears to have developed in relation to declining per caput availability of wild fish through overfishing and environmental degradation as population densities rose.
Wild fish is the major source of fish in most of Southeast Asia today as in the past, in contrast to the erroneous belief of widespread small-scale aquaculture. Most of Southeast Asia was sparsely populated until about a century ago except for the Red River delta in Northern Vietnam and Java in Indonesia. Aquaculture in both areas may be centuries-old and possibly have spread from China. Small-scale aquaculture is also traditional in terraced ricefields in the mountains of Northern Lao PDR and Northern Vietnam where limited land for rice and wild fish led to the early evolution of fish culture. Chinese traders appear to have introduced inland aquaculture, pond-based carp culture, to Malaysia, Philippines, Singapore and Thailand about a century ago. Small-scale cage culture probably evolved directly from capture fisheries a century ago in Cambodia through fishermen holding Pangasid catfish and snakehead in bamboo and wooden cages.
The oldest coastal aquaculture system in the world may be the Egyptian brackishwater pond system with a history of two to three millennia. The brackishwater culture of milkfish in ponds which is centuries-old in Indonesia, the Philippines and Taiwan reportedly originated in Java 600-800 years ago but there is also evidence of ancient fish culture by Polynesians in coastal lagoons. Culture of seaweeds began about 400 years ago in Japan; mollusc culture about 600 years ago in France and 300 years ago in Japan. While traditional, extensive culture of crustaceans is associated with that of milkfish, hatchery-based shrimp culture began only two decades ago. Most other coastal aquaculture is relatively recent, evolving from a few decades to less than a decade back
Global aquaculture production in terms of both volume and value has recently been reviewed in depth from 1984 to 1992, for which period aquaculture statistics separate from those of capture fisheries were submitted to FAO (1995) by Governments. These statistics indicate that aquaculture expanded from 8% to 14% of global fisheries production from 1984 to 1992. Total aquaculture production in 1992 was 19.3 million tonnes valued at US$32.5 thousand million. Developing countries accounted for most of this production, with Asia producing 84.0% and Africa 0.5% and Latin America 2.3%.
In terms of production of major commodity groups in developing countries, about 48% was finfish, 31% seaweeds, 16% molluscs and 5% crustaceans in 1992 (Csavas, 1994) with Asia dominating production in all groups. The distribution of production between inland and coastal aquaculture was almost equal at 44% and 56%, respectively, although their commodity distributions vary. More than 99% of inland aquacultural production was finfish although freshwater macrophytes are excluded from the statistics. In coastal aquaculture seaweed production was 56%, molluscs 28%, crustaceans 8% and finfish 7%.
As the statistics do not differentiate between culture systems, either by culture facilities or intensity of production, rural aquaculture production cannot be estimated. Although global finfish production is mostly freshwater carps, much of this is produced in China where intensified production has risen dramatically over the past decade, taking much of it beyond the realm of rural aquaculture. In fact such statistics may not include production from rural aquaculture since many small-scale farmers do not practice aquaculture in the conventional sense of regular stocking, harvesting and pond draining. They may be unable to culture fish throughout the year because ponds either dry up or become increasingly flooded due to unstable rainfall. Farmers usually harvest small amounts of fish at irregular intervals for household consumption and culture fish for longer than a year without draining the pond to conserve water for other purposes if they perceive that the pond holds sufficient numbers of fish. The multifarious factors relating to rural aquaculture preclude collection of statistics on production levels in the conventional terms of kg or tonnes/unit area/year as required for annual summaries of data.
The rural fish farmer is frequently invisible to the fisheries research and seed production centres. He purchases a few hundred to a few thousand fry, usually from middlemen in Asia. If he sells fish, it is within the equally invisible market of the village or local micro-market. His pond or fish-farming enterprise may be equally invisible, consisting of a paddy field, or backyard pond measured in only tens or hundreds of m2. Even satellite image interpretation cannot pick up such resources, let alone field surveys by understaffed departments of fisheries, but resources they are and crucially important to the farm family livelihood. By standard definitions, some of these micro-ponds in Asia should not be included in a discussion of rural aquaculture. Many such ponds are in fact traps, ranging from depressions to pits in and alongside paddy fields, acting as a sump into which water and fish are drained at the end of the rice planting season. While this practice has often been termed rice-fish culture it is the basis upon which several writers have claimed aquaculture to be an age-old practice in the region - in its original form, the practice is simple rice-field capture fishery, as much capture as setting a trap at a gap in the bund or dangling a line.
Rural fish production may well be grossly underestimated in Asia due to inadequate data. One example suffices to indicate the weak database: Fish production for Northeast Thailand estimated from actual fish consumption data was six times higher than official Department of Fisheries estimates (Mekong Committee, 1992).
Aquaculture has considerable growth potential based on recent trends. Global aquaculture production almost doubled from 5.2 to 10.1 million tonnes in the decade from 1975-1984 and again to 19.3 million tonnes from 1984-1992. This is a rate of almost 10% per year, much faster than the rate of growth of any other food commodity and even that of the human population. Most of these increases, however, have been in Asia, which dominates global production with about 50% of the total coming from China alone.
An important question in relation to the potential of small-scale aquaculture is the reason for Asian domination in production. The major reasons (Csavas, 1990) are the following:
The soaring human population in Asia is thus likely to lead to ever increasing interest in aquaculture in future. A similar trend is likely in Africa and Latin America, in particular where societies traditionally consume fish. However, aquaculture should be promoted in non-fish-eating societies to overcome social reluctance to grow and consume an unfamiliar food.
Aquaculture growth can be accelerated in two ways: increasing the area devoted to aquaculture; and intensifying production in existing aquaculture areas.
While there is now limited potential for agriculture to expand into new areas, in particular in Asia, in contrast there is considerable potential to increase the area allocated to aquaculture. Aquaculture may use swamps, saline soils and mangroves which are unsuitable for agriculture. It may also use inland aquatic resources such as natural and man-made lakes, reservoirs and rivers; it may use coastal areas. Aquaculture may also be introduced into irrigation systems and essentially only borrow the water. Perhaps the greatest potential for increasing the area of aquaculture is to integrate it with agriculture on good agricultural land and, through synergism, increase land productivity and profitability.
Increasing the area devoted to aquaculture may be carried out by a farming household already engaged in aquaculture but the major increase in production is likely to come from new entrants. Relatively few small-scale farming households practice aquaculture, even in Asia. Millions of small-scale farming households globally are potential new entrants to aquaculture, although there will obviously be market limitations to their entry.
Aquaculture production can also be increased by intensified production from existing production areas. Farm production may be low using only on-farm nutritional inputs because most small-scale farms are resource-poor. Increased production may require the use of off-farm inputs to satisfy growing farmer aspirations if the farmer intends aquaculture to contribute significantly to household welfare. Relatively low-cost technologies affordable to small-scale farmers have been developed. If extended widely, they could have a major impact on global aquaculture production.