The History and Current Status of Freshwater Prawn Farming
Shrimp News: I made a mistake when I originally posted this report. I assumed that the author of the report was writing about all freshwater prawn farming in China, when, in fact, he was just writing about the giant freshwater prawn, Macrobrachium rosenbergii.
Michael New, the world’s leading expert on prawn farming, pointed out the mistake. Here are his comments:
“....I have determined that the author makes it clear that he is only talking about the giant river prawn M. rosenbergii and does not describe the farming of the indigenous species, the oriental river prawn M. nipponense. I therefore have no problem with his article in World Aquaculture, except to note that his production data are three years out of date.”
“However, I do have an issue with the introduction that you yourself wrote on the page on freshwater prawn farming on your website, where you stated ‘China is the leading producer of farmed prawns in the world, with production approaching 150,000 metric tons a year in 2009....’ Your statement is wrong as it leads the reader to assume that the article concerns all species of freshwater prawns and that 150,000 metric tons was therefore the total production. This is not so. In fact, the production of M. nipponense is much greater, so the overall total is considerable.”
“The actual current (most recently available from FAO, 2012) data are as follows:”
Giant river prawn (M. rosenbergii): 124,713 metric tons valued at $593,633,900.
Oriental river prawn (M. nipponense): 237,431 metric tons valued at $1,130,171,700.
Total freshwater prawn production: 362,144 metric tons valued at $1,723,805,500.
Source: Email to Shrimp News International. Subject: Michael New's Comments on the Article "Freshwater Prawn Farming in China—History and Status”. Michael New. January 16, 2015.
Here's the Original, Uncorrected Report
More than 35 species of Macrobrachium occur in China, but the giant freshwater prawn, M. rosenbergii, and oriental river prawn, M. nipponense, account for most of the farmed production. M. rosenbergii was introduced into China from Japan in August 1976*, and in 1977, the Guangdong Province Fisheries Research Institute (now the Pearl River Fisheries Institute, part of the Chinese Academic of Fisheries Science) successfully reproduced the prawns and distributed a total of 79,600 postlarvae to 14 Chinese provinces. Commercial farming started in southern China and then gradually spread north and inland.
The start-up phase for giant freshwater prawn development in China occurred from 1976 to 1992. After obtaining seedstock from Guangdong Province, other provinces carried out farming and breeding experiments, but because the breakthroughs in hatchery production of postlarvae were first made in Guangdong Province and because it had a warm climate, farming was initially concentrated in the province’s Zhujiang Delta, which had 276 hectares of prawn ponds in 1991. In 1992, the province produced 598 metric tons of prawns from 520 hectares of ponds.
The industry entered a new phase of development in 1993 as the profitable farms in Guangdong enticed more and more farmers to enter the industry. Also in 1993, whitespot virus wiped out many marine shrimp (Penaeus chinensis) farms throughout China, so many shrimp farmers switched to prawn farming. In 1993, prawn production in Guangdong Province reached 2,601 tons from 1,533 hectares of ponds, which was 2.9 times the area and 4.3 times the production of 1992, making the province the biggest prawn producer in the country. Earthen pond culture was commonly used during this period and the yields were between 1,500 and 3,000 kilograms per hectare per year, with a mean profit of $6,410 to $9,615 per hectare. Profitability was twice that of traditional fish farming.
From 1993 to 2001, prawn production had an average annual growth rate of 65 percent, and China became the largest producer of prawns in the world, producing 111,282 tons in 2001, representing 65 percent of global production.
Production declined in 2002 and 2003 as a result of outbreaks of white tail disease (WTD). The pathogen was first found in prawn seed imported from Thailand to Guangdong Province in 1996. Thereafter, the disease spread rapidly to most hatcheries and culture farms throughout the country, causing widespread losses. The causative agent of WTD has been identified as Macrobrachium rosenbergii nodavirus (MrNV), an extremely small virus. Diagnostic techniques for WTD use reverse transcriptase-polymerase chain reaction (PCR) and TAS-ELISA [a diagnostic test using polyclonal antibodies].
After 2003, prawn production gradually recovered as a result of the development of specific pathogen free (SPF) seedstock, which prevented WTD epidemics. From 1976 to 2002, Guangdong Province was the country’s main producing region. In 2003, however, prawn production in Jiangsu Province exceeded that of Guangdong Province. Since then, Jiangsu Province has been the province with the greatest prawn production in China.
Freshwater prawn farming had another period of rapid development from 2004 to 2009. The production of cultured freshwater prawns increased rapidly with implementation of more intensive farming and improved culture techniques. The production area increased quickly during this period, especially near Gaoyou City in Jiangsu Province. In 2009, China’s production reached 144,467 tons, representing 63 percent of global prawn production. Currently the majority of prawn production is concentrated in the Yangtze River Delta (southern Jiangsu Province and northern Zhejiang Province) and the Pearl River Delta (Guangdong Province).
Current Status and Production Practices
The spectacular increase in prawn production in China resulted from increases in culture area and stocking density. By 2009, the area around Gaoyou City in Jiangsu Province became the heart of the prawn farming industry, producing 53,300 tons from 10,000 hectares on ponds with profits of $6,250 per hectare. The profitability stimulated more farmers to begin freshwater prawn culture.
A tropical species, M. rosenbergii is sensitive to low temperatures. The appropriate water temperature range is 22° to 32° C, and the temperature range for optimal growth is 29° to 31° C. When postlarvae are stocked, the water temperature should be above 20° C. In the Yangtze River Delta, stocking traditionally began at the end of May, and harvesting took place in October. Therefore, production was restricted to the 4-5 months of warm weather and only one crop could be cultured each year.
More recently, however, farmers in the Yangtze River Delta use ponds covered with plastic greenhouses to increase the water temperature, allowing stocking in early March. When some of the prawns reach market size, the ponds are harvested and the smaller animals are returned to ponds to grow larger. Rotating stocking systems and partial harvests have allowed farmers to extend the harvest season from two months to four months.
The first two batches of PLs are grown to juvenile size in heated greenhouses before stocking in plastic-covered outdoor ponds in March and April. The stocking density is generally 100-150 postlarvae per square meter. When the outdoor water temperature rises to above 20° C, the plastic covers are removed. A third batch of PLs may be stocked directly into outdoor ponds. Therefore, ponds are stocked with large, medium and small animals in outdoor growout ponds. Harvest of marketable prawns must be done periodically (every 10 days) to provide sufficient space for the smaller animals remaining in ponds to grow rapidly.
In general, ponds are first seined in late June. By late October, all ponds are drain harvested. Average production is 5,250 kilograms per hectare, although production of 7,500 kg/ha has been achieved, and the record is 9,000 kg/ha. Because the Chinese prefer fresh aquatic products, famers get higher prices for live prawns.
Some other culture methods include rice-prawn culture, polyculture with fish, polyculture with Pacific white shrimp (Penaeus vannamei) and polyculture with mitten crabs (Eriocheir sinensis). However, these culture systems are not common and are often only experimental.
Main Issues of Commercial Freshwater Prawn Farming
So far, no other country has produced prawns on the same scale as China, not even the countries in Southeast Asia that have native populations of the freshwater prawn. Nonetheless, China’s prawn industry has many problems:
Genetic Degradation: At present, all cultured stocks of M. rosenbergii in China are offspring of the original imports, a small number that contained only one broodstock pair and 48 postlarvae that were introduced from Japan in 1976*. The industry has relied on non-improved stocks for more than 30 generations. Little attention has been paid to genetic improvement. Broodstock are often collected directly from growout ponds. This causes a high level of inbreeding, which can have a negative effect on stock productivity. Currently, genetic degradation of the stock is indicated by slow growth rate, early sexual maturity, small animals and vulnerability to disease. Some female prawns become sexually mature at six grams, but fecundity is only 1,000-3,000 eggs from these females. Eggs obtained from these females often result in poor-quality offspring.
Shortage of Quality Seedstock: The total demand for good-quality seedstock is 20-30 billion postlarvae a year. The area around Gaoyou City in Jiangsu Province requires around 15 billion postlarvae a year. Before 2010, when sufficient seed was produced by hatcheries, the average price of seed was only $16 per 10,000 postlarvae. However, the price of high-quality seed increased to over $64 per 10,000 postlarvae after the outbreak of M. rosenbergii larval syndrome, which caused many private hatchery enterprises to close, resulting in a seedstock shortage.
Even more seriously, male postlarvae produced by some private hatcheries grew more slowly and completely stopped growing at six centimeters. The presence of large quantities of small male prawns led to reduced harvests and many farmers suffered severe economic losses. Farmers call these males “stone prawns” or “iron prawns”. Poor-quality prawn seedstock contributes to the abuse of antibiotics in prawn hatcheries.
New Disease Outbreaks: In the late 1990s, white muscle disease was reported in Guangdong Province, and it gradually spread to Guangxi municipality, Zhejiang Province, Jiangsu Province and Shanghai, causing mass mortalities in newly stocked ponds. Later, through the work of researchers, the causative agent of white muscle disease was determined to be a virus called MrNV. The development of SPF seed production technologies has been effective in preventing the white muscle epidemic.
Since February 2010, the prawn hatchery industry has experienced outbreaks of M. rosenbergii larval syndrome, leading to mass mortalities (80-90 percent) in larval stages. This disease spread across the country and many hatcheries closed. The supply of prawn seed decreased greatly, causing heavy economic losses to hatcheries and farmers. In 2010, national production of M. rosenbergii decreased by 13 percent, compared to 2009. In 2011, it dropped to 122,923 tons, which was 21,544 tons less than in 2009. Macrobrachium rosenbergii dicistrovirus (MrDV), a new pathogen, was the causative agent of the disease outbreak. Additionally a new spiroplasma disease has been found in growout ponds.
Genetic Improvement: It is widely accepted that genetic improvements are needed to sustain the economic viability of prawn farming in China. Traits such as body weight, survival rate, growth rate and disease resistance all need to be improved. Since the 1990s, few scientists have carried out studies on M. rosenbergii breeding. Research is needed on artificial selection, individual selection and family selection.
Hatchery Improvements: It is necessary to guarantee the quality of broodstock prawns to produce better-quality postlarvae. Since most hatcheries in China use broodstock directly sourced from growout ponds, selection standards should be taken into account for achieving healthy condition and body size of male and female brooders for overwintering indoors. Broodstock should be virus free. Hatchery water quality needs to be improved to increase survival to metamorphosis. Antibiotics should be prohibited.
Development of New Disease Prevention Systems: It is important to improve the disease diagnosis technology of M. rosenbergii and to perfect prevention and treatment systems, especially for viral diseases. At present, diagnostic techniques for WTD, using reverse transcriptase-PCR and TAS-ELISA methods have been developed. The development of SPF seedstock production technologies has been effective in preventing white muscle epidemics. The scientific research concerned with disease detection during seed production and growout farming should be strengthened and the detection technology of new pathogens needs to be improved.
The giant freshwater prawn industry has bright prospects for expansion in China, but continued growth will depend on the joint efforts of the government, scientific researchers and farmers; the development of SPF prawn production systems; and stable hatchery output of quality prawn seedstock. Commercial prawn aquaculture has great growth potential, particularly in areas where marine shrimp (Penaeus vannamei) farming has suffered setbacks from early mortality syndrome (EMS).
*Shrimp News: Since I thought China got its first prawn broodstock from the state of Hawaii in the United States, I asked Michael New (email email@example.com), the world’s leading expert on freshwater prawn farming, about the first prawn imports into China. Here’s what he said:
“I do not believe that the M. rosenbergii were introduced into China from Japan. Also I do not think Japan got them from Hawaii.
According to a chapter (with references) I wrote in our 2010 book, the first introduction of this species into China did occur in 1976, but from Thailand, NOT Japan. Much of their technology in China came from Thailand, too. Further introductions occurred in 1980 and 2001 from Thailand and in 2002 from Myanmar. On the other hand, this species was introduced into Japan from Malaysia, about 1967, NOT from Hawaii.”
Sources: 1. World Aquaculture (the quarterly magazine of the World Aquaculture Society). Editor-in-Chief, John Hargreaves. Farming of Giant Freshwater Prawn in China. Yang Ming (firstname.lastname@example.org, Shanghai Shencao Special Fisheries Development Company, 8888 Caolang Highway, Jinshan, Shanghai 201516, China). Volume 45, Number 4, Page 48, December 2014. 2. Email to Shrimp News International. Subject: China’s First Imports of Freshwater Prawns. Michael New. January 2, 2015. 3. Bob Rosenberry, Shrimp News International, January 4, 2015.