The giant freshwater prawn is the largest and fastest-growing freshwater prawn widely distributed in Indian rivers’ confluent of the sea. The Giant freshwater prawn, M. rosenbergii, has great demand both in national and international markets. It migrates between river and estuary.

1. Seed production of Freshwater Prawn Macrobrachium rosenbergii
Introduction: The giant freshwater prawn is the largest and fastest-growing freshwater prawn
widely distributed in Indian rivers’ confluent of the sea. The Giant freshwater prawn, M.
rosenbergii, has great demand both in national and international markets. It migrates between river
and estuary.
SYSTEMATIC POSITION
Class-Crustacean
Order- Decapoda
Family- Palaemonidae
Genus- Macrobrachium
Species- M. rosenbergii
General Biology: The sexes are separate, males are considerably larger having large
cephalothorax, and long and robust second chelate legs than females. Lives in tropical freshwater
environments influenced by adjacent brackish water areas. Food includes algae, molluscs, aquatic
insects, worms, and other crustaceans. Larvae mostly consume zooplankton (mainly minute
crustaceans), very small worms, and larval stages of other crustaceans.
Reproductive Biology: Females mature 3-4 times a year with a peak during the monsoon season
(June to September). Breeding occurs in freshwater and the female carries the fertilized eggs in its
brood pouch under the abdomen. The number of eggs which are laid depends also on the size of
the female. Female prawns of M. rosenbergii are reported to lay from 80 000 to 100 000 eggs
during one spawning when fully mature. They are incubated for 18-21 days, during which the color
of the eggs changes from orange to grey.

2. Production cycle of Macrobrachium rosenbergii-
Image Source: FAO. 2009. Macrobrachium rosenbergii. In Cultured aquatic species fact sheets. Text by
New, M. B. Edited and compiled by Valerio Crespi and Michael New. CD-ROM (multilingual).
Sex Determination
**Mature male prawns are considerably larger than the females and the second chelipeds are much
larger and thicker.
**The head of the male is also proportionately larger, and the abdomen is narrower. The head of
the mature female and its second walking legs are much smaller than the adult male.
**The genital pores of the male are between at the base of the fifth walking leg. The female genital
pores are at the base of the third walking leg.
**The pleura (overhanging sides of the abdominal segments) are longer in females than in males,
and the abdomen itself is broader. These pleura of the first, second, and third tail segments of
females form a brood chamber in which the eggs are carried between laying and hatching.

3. A ripe or ‘ovigerous’ female can easily be detected because the ovaries can be seen as large orange-
colored masses occupying a large portion of the dorsal and lateral parts of the cephalothorax.
Fig.: The female Macrobrachium rosenbergii carry eggs until they are ready to hatch; The eggs
change their color from orange to grey/black upon ripening.
Obtaining and selecting egg-carrying females: When freshwater prawn farms are in tropical
areas where adult prawns are available year-round, the word brood stock usually refers only to the
females that are kept in hatcheries until their eggs hatch, after which they are discarded or sold.
Some hatcheries also hold a supply of adult males. Few tropical farms maintain freshwater prawn
broodstock in dedicated ponds. Freshwater prawn eggs are carried under the tail of the adult female
prawn (known as ‘berried’ or ovigerous females) and are easily visible. They can be obtained by
cast netting but are frequently selected at times of partial or total harvest.
Berried females can also be obtained from rivers, canals, and lakes in areas where they are
indigenous (native). However, collecting ovigerous females from the wild often results in
considerable egg loss during transport, so many hatcheries prefer to use adjacent rearing ponds for

4. their supplies. In the wild, berried females are most abundant around the beginning of the rainy
season.
Sex ratio: Broodstock is stocked at about a 4:1 female-male ratio. Blue- and orange-clawed
males are preferred since these males are bigger and are able to mate more efficiently than
smaller males.
When freshwater prawns are introduced into an area where they are not found in the wild, great
care must be taken to follow national and international guidelines for introductions, including
quarantine.
From a hygienic point of view, it is better to import PL from sources where no diseases have been
reported, rather than berried females.
Berried females should be carefully selected. Choose animals that are obviously healthy and active,
well pigmented, with no missing appendages or other damage, and carrying large egg masses. The
ripeness of the eggs is also important. As the eggs ripen, their color changes from bright orange to
brown and finally to greyish-brown a few days before hatching. Those carrying brown to grey eggs
are the best ones to bring into the hatchery, as their eggs will hatch within 2 or 3 days.
Genetic improvement: Until recently, very little progress had been made in the genetic
improvement of Macrobrachium. Moreover, selecting eggs from only one part of the spawning
period could lead to a reduction in genetic variation and an increase in inbreeding. Most farmers
select larger females, which usually carry more eggs, but this may not be good practice. Selecting
fast-growing, berried females from ponds three months after they were stocked, rather than
choosing large females six months after stocking, has a positive genetic effect on weight at harvest.
Experiments have shown that cutting off one of the eyestalks (ablation) of female broodstock
increases the number of mature females in a captive broodstock and diminishes the time
between each spawn. Young females (about 4 months old after stocking at PL size) spawn about
20 days after eyestalk ablation and spawn again after about 30 days.
Managing the broodstock: In the tropics, where berried females are readily available, special
broodstock holding facilities within hatcheries are not necessary. in temperate zones where,
freshwater prawns are reared in the summer, indoor broodstock facilities are essential.

5. Disinfection: Broodstock should be disinfected upon arrival at the hatchery by placing them in
fresh water containing 0.2 to 0.5 ppm of copper sulfate or 15 to 20 ppm of formalin for 30 minutes.
Aeration should be provided during these treatments.
Salinity: Whether the berried females are obtained from a captive broodstock or from the wild,
they should be held in slightly brackish water (~5 ppt) at 25-30°C and preferably at pH 7.0-7.2
until the eggs hatch.
Temperature: Adult prawns can then be transferred to holding tanks that contain freshwater at an
optimum temperature of 27-31°C. Temperatures below 25°C promote fungal growth on the
eggs. Temperatures below the optimum also cause some eggs to drop and increase the time for egg
development. Temperatures above 30°C encourage the development of protozoa and other
undesirable micro-organisms.
Light: Light does not seem to affect egg hatchability, although direct sunlight should be avoided.
Diet: A nutritionally complete diet is essential to promote superior egg production and quality.
Commercially pelleted grow-out feeds can be used but need supplementation. Broodstock should
be fed at a daily rate of 1-3% of total biomass, adjusted to match consumption.
Hatching and Stocking Larvae: The hatching process is extremely pH-sensitive. pH may need
to be adjusted to 7.0-7.2 for hatching. pH outside this range appears to result in substantially
reduced hatching rates. To enhance water quality for the hatching larvae, it is recommended that
berried females should not be fed at all during the 2-3 day period prior to egg hatching.
One can hatch the larvae in a special broodstock holding system and then transfer them to larval
rearing tanks in 12 ppt water. In hatcheries operating recirculation systems, newly hatched larvae
(Stage I) are often harvested from the broodstock holding tank. In a simple flow-through hatchery
one can place females with brown to grey eggs directly into the larval tanks. Then, remove the
females after their eggs hatch.
As the eggs hatch, a process which is normally completed for the whole brood within one or two
nights, the larvae (free-swimming zoeae) are dispersed by rapid movements of the abdominal
appendages of the parent. M. rosenbergii larvae require brackish water for survival.

6. After hatching, Larvae are then removed from the collection tank and transferred to the hatchery
phase. Some hatcheries prefer to maintain their larvae in the same tank from stocking until the
harvest of PL. The advantage of this is that the larvae are not subjected to handling. Handling
brings with it the dangers of damage to the larvae and physical losses during the transfer operation.
Stocking density: 50-100 larvae/L. Water quality parameters (Dissolved oxygen >3 ppm and
Ammonia <0.1 ppm) should be maintained.
One must select berried females that are all in the same stage of ripeness. This ensures that
larval tank will contain larvae of the same age (within 1-3 days) thus reducing cannibalism and
making a proper feeding schedule applicable.
Feeding: A wide variety of feeds can be provided, including the nauplii of brine shrimp (Artemia
spp.), a freshwater cladoceran (Moina spp.), fish eggs, squid flesh, frozen adult Artemia, flaked
adult Artemia, fish flesh, egg custard, worms, and commercial feeds. Most freshwater prawn
larvae do not feed on the first day (hatching day).
There are a number of microscopically distinct stages during the larval life of freshwater prawns,
which lasts several weeks. On completion of their larval life, freshwater prawns metamorphose
into post larvae (PL).

7. Sources of this note:
New, M. B. (2002). Farming freshwater prawns: a manual for the culture of the giant river prawn
(Macrobrachium rosenbergii) (No. 428). Food & Agriculture Org.
Alam, M.S., & Alam, M.N. (2014). Development of the giant freshwater prawn Macrobrachium
rosenbergii (De Man 1779) broodstock in culture ponds of South-Western Bangladesh: a
case study. Journal of entomology and zoology studies, 2, 108-113.
Cuvin-Aralar, M. L. A., Laron, M. A., Aralar, E. V., & Ursan, C. (2011). Breeding and seed
production of the giant freshwater prawn (Macrobrachium rosenbergii). Iloilo,
Philippines: Aquaculture Department, Southeast Asian Fisheries Development Center.
Some other useful sources for further study on this topic:
1. Mohamed, K. H. (1983). Hatchery production of prawn seed.
Link: http://eprints.cmfri.org.in/8495/1/K_H_Mohamed_117-137.pdf
2. Breeding biology and hatchery management of giant freshwater prawn (Macrobrachium
rosenbergii) Gulshan Kumar School of Fisheries
Link: https://courseware.cutm.ac.in/wp-content/uploads/2020/06/Session-7.-Theory-Breeding-
MR.pdf
3. Soundarapandian, P., Prakash, K. S., & Dinakaran, G. K. (2009). Simple technology for the
hatchery seed production of Giant Palaemonid Prawn Macrobrachium rosenbergii (De
Man). International Journal of Animal and Veterinary Advances, 1(2), 49-53.