‘Tambak’ is the common Indonesian name for a brackish water fish pond, classically supporting a polyculture of milkfish (Chanos chanos) and brackish water shrimp. There is historical evidence of 400-year-old tambak in South Sulawesi, naturally constructed in the lower meanders of river estuaries. Not until 1964, in response to increasing demand from Japan for shrimp (a result of post-World War II affluence) did large-scale expansion and intensification of culture occur in tambak. In 1984/85, the Indonesian central government developed policies to ramp up expansion and intensification, through the INTAM program, which targeted twelve provinces in Indonesia. Much of the increase in tambak coverage took place in mangrove forests, as both mangroves and tambak require tidal flooding and adequate drainage.
Tambak can be a massive feature in the coastal landscape, understood by anyone flying into a major deltaic city in Indonesia such as Jakarta, Surabaya, Lampung or Makassar. The 16,000+ hectare tambak complex owned by PTCP Prima Genjot (a subsidiary of the Thai conglomerate Charoen Pokphand) in Lampung is the largest contiguous aquaculture complex in the world, having displaced a mangrove system itself worth an estimated USD 436 – 574 million when one considers the value of mangrove goods and services (Sathirathai and Barbier, 2001).
As mangroves were replaced by tambak, a new set of social, economic and environmental problems arose. Services once provided by mangroves, such as flood control, saltwater buffering, and natural primary productivity were lost. Mangrove detritus (leaf-fall, dead roots and twigs) provides a food source for numerous plankton, animals and bacteria, which drives the near-shore or coastal food chain. Especially notable was the reduction in beneficial animal plankton, including copepods, which are an important food for shrimp and juvenile fish.
Lacking the basis of natural primary productivity, fish farmers must resort to external sources of nutrients to drive food production. Two of the most expensive purchases for fish farmers include both fish feed and fertilizer. With regards to feed, the majority of fish feed for milkfish and prawn production in Indonesia is imported. To “increase competitiveness” of aquaculture product exports, milkfish and prawn feed enters the country tariff-free, a policy which in practice reduces the likelihood of domestic production of these inputs. Resultantly, fish farmers become fully reliant on external, imported resources. With regards to fertilizer, traditional milkfish farmers historically applied organic sources of nitrogen to develop an algal mat on the tambak bottom, algae being the main food source for milkfish.
However, semi-intensive and intensive ponds required higher levels of production, so government aquaculture extension agents promoted the application of urea (along with TSP, industrial feed, antibiotics and pesticides) in an aquacultural intensification effort known as the “Blue Revolution”. Continued use of and reliance on industrially produced inputs have numerous downsides for rural fish farmers. On average, fish farmers in South Sulawesi have increased their use of urea 10-fold over the past decade, reaching heights of one tonne of urea per hectare at a cost of US$ 200. Less than half of urea is actually nitrogen (46%), with the other half composed of filler, useless as a fertilizer, which can be harmful to beneficial biological, chemical, and physical properties of the pond substrate. One member of a fish farmer field school in South Sulawesi likened these additives to cement, hardening pond bottoms, and killing off beneficial bacteria and other organisms which would normally enhance a ponds ecology and productivity.
Due to the high cost of imported fish feed, Indonesian farmers sometimes use expired noodles and crackers as a replacement, which has little nutritional or protein value. Resultantly, farmers are finding themselves continuously facing low growth rates coupled with high incidence of disease and mortality. Since the late 1990’s, indeed, tambak farmers in South Sulawesi have found themselves at constant risk of losing much or all of their harvest to death and disease, without fully understanding the reasons why. Research from the 1990’s revealed a pair of common shrimp viruses afflicting Penaeus monodon (tiger prawn) the most commonly cultured shrimp. The government’s eventual response was to promote alternate species of shrimp, which in recent times includes promotion of the use of Litopenaeus vannamei, a white shrimp native to the Pacific coast of the Americas from Mexico to Peru, which is often claimed (incorrectly) to be “disease resistant”. The introduction of vannamei, as it is locally known, has actually introduced additional diseases to Indonesian waters, such as Taura syndrome virus.
The answer to shrimp disease is not likely the introduction of genetically “resistant” stocks but rather related to environmental factors. Several authors have expressed that ecological collapse is likely in mangrove areas, where more than 20% is converted for other uses such as aquaculture development. Yet the twelve provinces mentioned as targets for aquaculture development in the INTAM program already experienced an average of 60% conversion of mangroves to aquaculture during by 1982, with half of those provinces having already experienced 80-99% conversion. The continued unbalanced use of exotic species and external, industrial inputs in this system, without a move back towards naturalness (a mosaic of land uses include native habitats and development of organic aquaculture practices) can only lead to further degradation of ecological links, reduced productivity, and increased incidence of disease.
Since the spread of the above-mentioned viruses, rearing shrimp has a high risk of mortality. Still, many fish farmers try to achieve higher production, by adding more urea to their ponds, up to one tonne per hectare per cycle. Haji Haruna has farmed fish in Bontomanai Village, Pangkep District, South Sulawesi for the last 40 years. He says the last 15 years have been difficult. Like his neighbors, he had continued to increase the use of urea (about ten times as much in ten years) without notable increase in yields, and with a high risk of losing the crop to disease. A few years back he experienced a three year period where his crop failed entirely and he made no income from fish farming. He suspected overuse of urea was harming his pond, either the water quality or substrate. He began, on his own, to use chicken manure instead of urea, and could once again grow fish and shrimp in his ponds. He joined a fish farmer field school two years ago (in 2011), and has continued use of organic inputs only. He is happy that he can farm again, while all other neighbouring farmers who still use urea and other industrial inputs have experienced high and even total mortality in the past two years.
This is an excerpt from Fish Farmer Field School, which we wrote for Aquaculture Asia Magazine. Read the full article in PDF and/or explore many other such articles in our resources section.