World Aquaculture - December 2014

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50 DECEMBER 2014 • WORLD AQUACULTURE •
Some other culture modes include rice-prawn culture,
polyculture with fish, polyculture with Pacific white shrimp
Litopenaeus vannameiand polyculture with crab Eriocheir sinensis.
However, these culture systems are not large and often used only in
experimental research, according to local conditions, and have not
been developed on a large scale.
Main Issues of Commercial Freshwater Prawn
Farming in China
The giant freshwater prawn has been grown in China for more
than 30 years. So far, no country other than China has such an
extensive farming area, even in the natural range of this species in
other countries of Southeast Asia. Nonetheless, there are problems
in the freshwater prawn industry of China. If these problems
cannot be solved, they will have a serious negative influence on the
sustainable development of prawn farming in China.
Genetic degradation. At present, all cultured stocks of M.
rosenbergii in China are offspring of the original stock, a small
group containing only one pair of broodstock and 48 postlarvae that
was introduced from Japan in 1976. Since then, the giant freshwater
prawn culture industry relies on non-improved stocks after more
than 30 generations of reproduction. Little attention has been paid
to genetic improvement in culture stocks. Broodstock are often
collected directly from grow-out ponds. This phenomenon causes a
high level of inbreeding, which can have a negative effect on stock
productivity. Genetic diversity in cultured stocks is low as a result of
inbreeding (Schneider et al. 2013). Genetic degeneration of the stock
is indicated by slow growth rate, early sexual maturity, individual
miniaturization and vulnerability to disease. Some female prawns
become sexually mature at 6 g but fecundity is only 1,000-3,000
eggs in these small mature females (Fig. 2). Eggs obtained from
these females often result in poor-quality offspring.
Lack of quality seed.Healthy and otherwise good-quality seed is
the basis of sustainable development of the giant freshwater prawn
farming industry. In China, the annual production of the giant
freshwater prawn is over 100,000 t. The total demand for good-
quality seed is 20-30 billion post-larvae. The particular demand for
prawn seed is greatest near Gaoyou city, Jiangsu Province, the most
important M. rosenbergii culture region and where demand for seed
is around 15 billion post-larvae. Before 2010, when sufficient prawn
seed could be produced by hatcheries, the average price of seed was
only US$ 16 per 10,000 post-larvae. However, the price of high-
quality seed increased to over US$ 64 per 10,000 post-larvae after
the outbreak of M. rosenbergii larval syndrome, which caused many
private hatchery enterprises to close, resulting in a shortage of seed.
Even more serious is that post-larvae produced by some private
hatcheries grew slower than normal prawn seed, even stopping
growth at 5-6 cm, leading to a smaller harvest size. These male
prawns had the remarkable characteristics of a larger cephalothorax,
longer second chelipeds, smaller abdomen (small edible portion),
all similar to old blue-claw males (Ranjeet and Kurup 2002). The
presence of large quantities of small male prawns led to a reduction
of output and many farmers suffered severe economic losses. Local
prawn farmers called this prawn type “stone prawn” or “iron prawn.”
Finally poor-quality prawn seed contributes to the abuse of antibiotics
in prawn hatcheries. An inadequate supply of quality seed is a major
constraint to the healthy development of freshwater prawn faming in
China.
New disease outbreaks. In the late 1990s, whitish muscle disease
was first recorded in Guangdong Province, spreading gradually to
Guangxi municipality, Zhejiang Province, Jiangsu Province and
Shanghai. These disease outbreaks caused mass mortality in post-
larvae ponds within a few days and serious economic losses in many
prawn hatcheries and prawn farms (Qian et al. 2006 b). Later, through
the work of scientific researchers, the causative agent of whitish
muscle disease was determined to be a virus called MrNV (Qian et
al. 2003 a). The development of SPF seed production technologies
has been effective in preventing the whitish muscle epidemic.
However, since February 2010, the giant freshwater prawn seed
production industry in China has suffered a severe recession from
outbreaks of M. rosenbergii larval syndrome in many hatcheries,
leading to mass mortality (80-90 percent) in larval stages. This
disease spread across the country and many hatchery enterprises
have closed down. The supply of prawn seed decreased greatly,
causing heavy economic losses to hatcheries and farmers and brought
tremendous constraints to the development of the freshwater prawn
industry. The national production of M. rosenbergii in 2010 decreased
by 13 percent compared to 2009. In 2011, the farmed production
decreased further to 122,923 t, which was 21,544 t less than in 2009.
Macrobrachium rosenbergii dicistrovirus (MrDV), a new pathogen,
was the causative agent of the nationwide infectious disease outbreak
(Pan et al. 2010). Additionally a new spiroplasma was found in
diseased giant freshwater prawns in grow-out ponds (Liang et al.
2011).
Suggested Solutions
Effective measures must be taken to insure the healthy and
sustainable development of the freshwater prawn farming industry in
China.
Genetic improvement of giant freshwater prawn. It is widely
accepted that genetic improvement is the effective method to improve
economically important traits in M. rosenbergii. Now, traits such
as body weight, survival rate, growth rate and disease-resistant
performance are often used as important economic traits in genetic
improvement programs. Since the 1990s, few scientists have carried
out studies on M. rosenbergii breeding. The methods of new variety
selection include crossbreeding, artificial selection, individual
selection and family selection. Selection programs for new varieties
of M. rosenbergii are an effective method to achieve sustainability of
giant prawn farming.
Improvement of quality-seed production systems. It is necessary
to guarantee the quality of broodstock prawns to produce better-
The giant freshwater prawn has been grown in China for more than 30 years. So far, no country other
than China has such an extensive farming area, even in the natural range of this species in other countries
of Southeast Asia. Nonetheless, there are problems in the freshwater prawn industry of China.