World Aquaculture - December 2014

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• WORLD AQUACULTURE • DECEMBER 2014 49
vannamei, was cultured at a large
scale in Guangdong Province, with the
farming area expanding quickly at that
time. Although thought of as a marine
penaeid shrimp, L. vannamei can also
be cultured in fresh water, so it soon
outgrew M. rosenbergii and became
the most popular culture species with
the farmers of Guangdong Province.
Freshwater prawn farming had
another period of rapid development
from 2004 to 2009. The production of
cultured freshwater prawn increased
rapidly with implementation of more
intensive farming and improved
culture techniques. The production
area increased quickly during this
period, especially near Gaoyou city,
Jiangsu Province. In 2009, production
reached 144,467 t, 63 percent of
global farmed giant freshwater prawn
production (Fig. 1). Currently the
majority of giant freshwater prawn
production is concentrated in the
Yangtze River Delta and Pearl River
Delta.
Current Status and
Production Practices
The spectacular increase in
giant freshwater prawn production
is partly the result of the increase in
culture area and rapid development
of intensive culture. China’s biggest
giant freshwater prawn culturing and
producing region is near Gaoyou City,
Jiangsu Province. There, in 2009,
the farming area reached 10,000 ha with a production of 53,300
t, and farming profit increased to US$ 6250/ha. The profitability
stimulated more farmers to begin freshwater prawn culture.
As a tropical species, M. rosenbergii is sensitive to low
temperature. The appropriate water temperature range is 22-32 C
and the temperature range for optimal growth is 29-31 C (Chen
et al. 1981, New 1990). When post-larvae are stocked, the water
temperature should be above 20 C. Post-larvae of M. rosenbergii
cultured in outdoor ponds in the Yangtze River Delta region
can only be stocked at the end of May because of temperature
restrictions. Marketable prawns are harvested in October when
water temperature falls below 20 C. Therefore, only a single crop
of freshwater prawn can be cultured in a year in China because
production is restricted to the 4-5 months of warm weather.
Continuous innovations in aquaculture technology and many
new efficient farming modes have been developed by the joint
efforts of researchers and farmers. With the great progress in
farming technology, the stocking density of M. rosenbergii also
has increased. In general, increased stocking density results in an
increase in production and higher revenues, enhancing economic
performance substantially.
At present, local farmers in
the Yangtze River Delta region
use ponds covered with plastic
greenhouses to increase water
temperature, allowing stocking of
seed in spring (generally in early
March). This system is combined
with selective harvest and multi-
stage rotational stocking systems to
allow increased production. When
prawns reach market size, they
are selectively seined and smaller
animals are returned to ponds. This
method allowed sufficient time
for grow-out of smaller prawns
remaining in ponds. Through
stocking ponds in batches, prawns
can be provided continuously to
the market. Prawn famers can get
higher profits by selling live animals
in the market, inasmuch as the
Chinese prefer to cook fresh aquatic
products (Yang et al. 2012). These
measures improve yield and extend
the marketing time of fresh aquatic
products from two months to more
than four months. The influences
of improved unit yield and earlier
marketing of commodity prawns on
enhanced economic performance
are substantial.
Most prawn farmers stock seed
into plastic-covered greenhouses
during March and April every
year. The stocking density is
generally 100-150 PL/m2 during
the culture period. The first batch of PLs, grown to juveniles, is
acclimatized in heated greenhouses before stocking in outdoor
grow-out ponds. After about one month, the first batch of PLs
grows to 3-cm juveniles and the second batch of PLs is moved
into nursery greenhouses. When the outdoor water temperature
exceeds 20 C, plastic-covered greenhouses are removed and all
juveniles are stocked into outdoor ponds. If desired, a third batch of
PLs is stocked directly into outdoor ponds as supplementary seed.
Therefore, ponds are stocked with large, medium and small animals
in outdoor grow-out ponds. Harvest of marketable prawns must
be done periodically (every 10 days) to provide sufficient space for
smaller animals remaining in ponds to grow rapidly.
In general, ponds are first seined in late June. Larger,
commercial-size prawns are selectively harvested and smaller
ones returned to ponds. Selective harvest of larger animals can be
effective for increasing total yield. Ponds are drained and all animals
sold before late October. Average production is 5,250 kg/haby this
system. Greater production is over 7,500 kg/ha and the highest can
reach 9,000 kg/ha.
( C O N T I N U E D O N P A G E 5 0 )
FIGURE 2. An early maturing female Macrobrachium rosenbergii.
The spectacular increase in giant
freshwater prawn production is partly
the result of the increase in culture
area and rapid development of intensive
culture. China’s biggest giant freshwater
prawn culturing and producing region
is near Gaoyou City, Jiangsu Province.
There, in 2009, the farming area
reached 10,000 ha with a production
of 53,300 t, and farming profit increased
to US$ 6250/ha. The profitability
stimulated more farmers to begin
freshwater prawn culture.