Fresh Water Prawn Culture

About fresh water prawn
Fresh Water Prawn (Macrobrachium malcolmsonii), the second largest fast-growing
prawn occurs commonly in Indian rivers, draining into Bay of Bengal. They are cultivated under
monoculture as well as polyculture systems. Under monoculture systems production levels of
750-1,500 kg prawns/ha/ 8 months are achieved. Further, it is a compatible species for polyculture
along with Indian Major Carps and Chinese carps, which may yield 400 kg prawns and 3000 kg
carps/ha/yr. Since the seed requirement for the commercial farming of this species is not met from
the natural resources, large-scale seed production under controlled conditions for year-round
supply is extremely important. The technologies of large-scale seed production and grow-out
culture have led to increased awareness of the farmers and entrepreneurs for diversification of their
culture practice.

Broodstock Management
Broodstock and berried females are essential component for continuous operation for seed
production. The gonadal maturation of the species differs greatly in nature depending on the agroclimatic conditions. In the Ganga, the Hooghly and the Mahanadi river systems, the maturation and
breeding start from May and continue till the end of October, whereas in the Godavari, the Krishna
and the Cauvery systems it commences from April and continue till November. Under pond
conditions, sexual maturity generally occur after attaining a maximum size of 60-70 mm. Berried
females are recorded year-round in most of the ponds. The ratio of berried females in total
population is found to be higher during August-September and during this period they carry good
quantity of eggs (8000-80,000). Prawns breed 3-4 times in a season. Successful community
breeding and year-round seed production under captive conditions is possible by employing air-lift
bio-filter re-circulatory system.

Spawning and Larval Rearing
Mating takes place immediately after pre-mating moult in matured female and spawning
occurs few hours after mating. Incubation period of eggs lasts between 10-15 days depending upon
the water temperature of 28-30°C. However, at lower temperature, the incubation period is
prolonged to more than 21 days. Hatching of fully developed 1st zoea takes place through the body
stretching of the zoea, which breaks the eggshell and comes out from the egg and starts swimming
as plankton.
Different larval rearing technologies viz., static, flow-through, clear or green water, closed
or semi-closed, with or without circulation systems of larval rearing of prawn species under
hatchery conditions have been developed with varying degrees of success. The green water
technique has been claimed to increase the post-larval production by 10-20% over other techniques
and provide a quality seed. But higher mortalities are generally encountered due to rise in pH and
uncontrolled algal bloom. Further, increase in numbers of adult Artemia, due to abundance of feed
in green water, contributes to accumulation of ammonia in the culture medium. The production of
post-larvae (PL) in large numbers is possible following airlift bio-filter re-circulatory system. The
larvae passed through 11 zoeal stages before attaining PL within a period of 39-60 days at salinity
and temperature ranging from 18-20‰ and 28-31°C, respectively, with the production density of
10-20 PL/l.

Bio-filter equipped with air-lift re-circulation has shown promising results in maintaining
favorable water quality in different rearing media with enhanced rate of post-larval production. The
water quality parameter generally influences the growth, survival and metamorphosis of the
developing larvae and it should be maintained optimally for getting better survival .

Larval Feeding
Various feed items viz., Artemia nauplii, zooplankton especially cladocerans, copepods,
rotifers, flesh of prawn and fish, molluscan meat, earthworms, tubificid worm, egg custard and cut
pieces of goat/hen viscera are used during larval rearing. Among these Artemia nauplii have been
recognized as an excellent larval food for the prawn larvae. At the beginning, freshly hatched
Artemia nauplii are provided to the 1st stage zoea at 1 g/30,000 larvae twice daily up to 15 days or
till they attain stage VI. Thereafter, the feed is given once daily along with egg custard and mussel
meat/tubificid worm four times daily.

Harvesting of Post-larvae
Harvesting of post-larvae of prawn is rather difficult due to their crawling habit. Therefore,
both turn-down and drain siphoning of water are commonly used for harvesting. But due to longer
duration for attaining post-larval stage the above methods are neither useful nor safe. Further, the
presence of post-larvae in the larval tank affects the growth and survival of advanced larvae due to
competition for food and cannibalism. Hence, the need for an ideal device for regular harvest of
post-larvae from the rearing unit is very much essential. String shell is therefore devised and is
successfully used for phase wise harvest of post-larvae during larval rearing. Post-larval survival
and production rates, following air-left bio-filter re-circulatory system, are in the range of 10-20
PL/l.

Post-larval Rearing
Optimum growth, production and survival of prawns can be achieved in grow-out ponds
on stocking the nursery reared juveniles rather than stocking directly with the freshly
metamorphosed post-larvae. Post-larvae slowly adopt themselves to freshwater. Optimum growth
and survival of healthy juveniles during post-larval rearing is achieved at salinity of 10parts per
thousand.

Post-larval rearing can be done both in well-prepared earthen ponds with adequate
aeration facility and inside the hatchery following bio-filter re-circulatory system. Stocking
density, feed and water quality management play the major role in raising healthy juveniles during
rearing. Stocking density between 10-15 PL/l is ideal. Among various feed items, egg custard
along with chopped freshwater mussel meat have been established to be more effective in
maintaining good growth. Water quality parameters, viz., water temperature, pH, dissolved
oxygen and dissolved ammonia in the ranges of 27.5-30ºC, 7.8-8.3, 4.4-5.2 ppm and 0.02-0.03
ppm, respectively are considered to be favorable for better survival.

Grow-out Culture
Grow-out system of prawn is normally comparable to that of freshwater fish farms. As the
prawns can migrate from one pond to other due to its crawling habit, it is necessary to have the pond
embankment 0.5 m higher from the water level. Sandy-clay pond bottom is considered to be
favourable for better growth. Undrainable ponds may be treated with conventional piscicides for
eradication of predatory and weed fishes. Stocking density of 30,000 to 50,000/ha is recommended
for semi-intensive monoculture farming. Ponds with the facility of water exchange and aeration
can be used for intensive farming where stocking density could be increased to 1 lakh/ha.
Temperature is the most important factor which directly controls the growth and survival of
prawns. Temperatures above 35°C or below 14°C are generally reported to be lethal and 29-31°C is
optimal.
Male prawns grow faster than females. Mixture of groundnut oil cake and fish meal in the
proportion 1:1 is used as supplementary feed. A production of 750-1200 kg/ha in six months of
rearing are achieved under monoculture with the stocking density of 30,000-50,000. In
polyculture, M. malcolmsonii at a stocking density of 10,000-20,000/ha along with carps at density
of 2,500-3,500 nos/ha, a production of 300-400 kg prawn and 2000-3000 kg carps can also be
raised.

Fresh Water Prawn Culture

Related Posts

Aquaculture and Its Type for Competitive exam

Economic Importance of Fish

Economic Importance of Fish in Detail

Leave a Reply Cancel reply