freshwater prawn farming: global status, recent research...

Freshwater prawn farming: global status, recent

research and a glance at the future

Michael Bernard NewAquaculture without Frontiers, Marlow, UK

Correspondence: M B New, OBE, Aquaculture without Frontiers, Wroxton Lodge, 25 Institute Road, Marlow, Bucks SL7 1BJ, UK.

E-mail: [email protected]

Abstract

A review of the current status of freshwater prawnfarming globally, with comments on the statistical in-formation available is provided in this symposiumkeynote paper. A brief overview of the research onfreshwater prawn farming that has been publishedin international journals since 2000 is also provided.Finally, some research needs are listed and some sce-narios for future expansion are explored.

Keywords: freshwater prawns, Macrobrachium,global, status, future

Introduction

I am honoured to have been invited to make the key-note address at this most important symposium. Myinterest in freshwater prawns has been a kind of ob-session. I have beenworking with freshwater prawnssince 1969 here in Asia, and in North and SouthAmerica, the Caribbean and Europe. I have writtenmany reviews and articles about this topic. Perhapsmy best-knownpublication has been the FAOmanualon freshwater prawn farming that my Thai co-man-ager, Somsak Singholka and I wrote in the 1980s(New & Singholka 1985). This was translated intoFrench, Spanish, Farsi, Vietnamese and Hindi. How-ever, over the past 20 years it naturally becamesomewhat out of date. In 2000,WagnerValenti and Iedited what is probably themost up-to-date referencetext on the topic (New & Valenti 2000). More recently,FAO asked me to write a new manual on freshwaterprawn culture (New 2002a). I hope that this too willeventually be issued by FAO in other languages andtranslated by others into additional languages, in-cluding Indian languages. Dr C. MohanakumaranNair has kindly agreed to help in this latter task.

My paper reviews the current global status offreshwater prawn farming, summarizes some of thenews and research papers on this topic that havebeen published since my book was issued (New &Valenti 2000), and makes a tentative glance into thefuture.

Current global status

First of all this morning, I would like to talk about theglobal production data. There has been a very rapidglobal expansion of freshwater prawn farming since1995 (Fig. 1). This is mainly because of the huge pro-duction of China but also, in the last few years, be-cause of a rapid take-o¡ of farming in India andBangladesh.The top15 producers in 2001are shown inTable1.

Chinawas by far the leader with over128300mt.VietNam was second in this league table (28000mt) butthe actual production level is a little uncertain be-cause it is included in the general FAO category fresh-water crustaceans not elsewhere included (nei).However, I believe that most of this consists ofMacro-brachium rosenbergii production so I have includedit in Fig. 1 and Table 1. India came third, with over24200mt in 2001, according to FAO. Last month itwas reported (Anonymous 2003c) that 35000mtwere exported from India in 2002.The next three places are taken by Thailand, Ban-

gladesh (which is a major exporter of wild-caughtfreshwater prawns) and Taiwan. Thailand andTaiwan were both pioneers in freshwater prawnfarming. The FAO ¢gure for Brazil is a times 10 errorin the statistics. Recently I was in Brazil and I con-¢rmed that current production is in the order of500mt year�1, not 5000mt year�1. The ¢gurefor Ecuador is also suspect; it has remained exactlythe same for the last 7 years. Malaysia, where the life

Aquaculture Research, 2005, 36, 210^230 doi:10.1111/j.1365-2109.2005.01237.x

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cycle ofM. rosenbergiiwas ¢rst closed, is nowa majorproducer. The other countries are quite modest pro-ducers so far.Figure 2 shows the production of M. rosenbergii

in Asia; output in China dwarfs the scale of otherproducing countries. After China, India, Viet Nam,

Thailand, Taiwan and Bangladesh are the mainproducers. Production in Thailand is starting to riseagain. Production in Malaysia, although relativelysmall compared with other Asian countries ex-panded rapidly between1997 and 2000 but fell backsomewhat in 2001. Expansion has been much morerapid in India and Viet Nam than elsewhere. In theIndian State of Andhra Pradesh alone, production isnow 27000mt (Anonymous 2003a), up from 400mtonly 5 years ago. Further substantial expansion is ex-pected, as I am sure we shall hear in this symposium.Most freshwater prawns are produced in Asia but,

as shown in Fig.3, Chinese production is much morethanall the otherAsian countries put together.Threespecies are currently grown in inland waters inChina; two are Macrobrachium spp. but the other isthemarine shrimp Penaeus vannamei.Macrobrachiumnipponense is common in Chinese inland capture¢sheries. Its maximum size is 86mm for malesand 75mm for females. It can naturally reproducein freshwater and it is one of the few Macrobrachiumspecies that has a temperate distribution. Thesefacts, and its popularity with Chinese consumersmake it attractive to farm. However, M. rosenbergiiis regarded as themajor species for the export marketfor freshwater prawns that China hopes to develop.Although some work on its culture was reportedin the1970s, real commercial production ofM. nippo-nense did not begin until the 1990s at about thesame time as the culture of M. rosenbergii beganto take o¡ in China (W. Miao, pers. comm. 2003).By now, the quantity of M. nipponense produced infarms is about the same as that obtained fromthe capture ¢shery. Estimated production of the indi-genousM. nipponense is rapidly catching up with the

0

50,000

100,000

150,000

200,000

250,000

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Figure 1 Expansion of freshwaterprawn (the FAO data include thecategories giant river prawn,freshwater shrimps/prawns nei andfreshwater crustaceans nei) farming1992^2001 (mt) (FAO 2003).

Table 1 Top 15 countries farming freshwater Macrobra-chium rosenbergii� in 2001 (FAO 2003)

# Country

Farmedproductionin 2001 (mt) Notes

1 China 128338

2 Viet Nam 28000 Freshwater crustaceans nei

(thought to be mainly

M. rosenbergii)

3 India 24230

4 Thailand 12067

5 Bangladesh 7000

6 Taiwan 6859

7 Brazil 5380 � 10 error in FAO’s 2001

statistics (Brazil was really #9,

after Malaysia)

8 Ecuador 800 Possibly incorrect?

9 Malaysia 752

10 Dominican Rep 62

11 Guatemala 53 Includes 3mt of other

freshwater prawn species

12 Senegal 50

13 Mexico 48

14 USA 44

15 French Guiana 25

Others 153

�The FAO data includes the categories giant river prawn, fresh-water shrimps/prawns nei and freshwater crustaceans nei.nei, not elsewhere included.

Aquaculture Research, 2005, 36, 210^230 Overviewof freshwater prawn culture in USA MBNew

r 2005 Blackwell Publishing Ltd, Aquaculture Research, 36, 210^230 211

production of the introduced M. rosenbergii (Fig. 4).So far, China has not reported its production ofM. nipponense in its o⁄cial statistical returns toFAO. An estimated production of 15000mt ofthis species was reared in China in 1999 (Wang &Qianhong 1999) and 120000mt in 2001 (W. Miao,pers. comm. 2003). In addition to these two species,experimental culture of one of your own indigenousprawns in India, M. malcolmsonii, has startedin China.Recorded production in Central and North Ameri-

can countries is quite small (Fig.5). Only four nationsproduced more than 40mt in 2001 ^ the DominicanRepublic, Guatemala, Mexico and the USA. Figure 6shows the data for South America. The ¢gures forBrazil have been adjusted but I have not changed theFAO ¢gures for Ecuador, although I remain scepticalabout them. The encouraging thing is that produc-

tion in Brazil, after declining between 1993 and1999, now seems to be increasing again. The Brazi-lian government has been concentrating on the pro-motion of marine shrimp farming but it is hoped thatit may now become also interested in a form of aqua-culture that may be more sustainable, namely theculture of freshwater prawns. One of the universitiesthere has a large team working not only on the cul-ture of M. rosenbergii but also on an indigenous spe-cies, M. amazonicum, which is thought to have greatpotential for small-scale farms in the Amazonia re-gion, where it is a feature of the capture ¢shery. Themaximum size ofM. amazonicummales has beenvar-iously reported as110^150mm, while the maximumfemale size recorded is110mm.There is very little production outside Asia and

South and Central America (Fig. 7). Senegal andMauritius, both in Africa, are the leaders but their

0

20000

40000

60000

80000

100000

120000

140000

BANGLADESH

CHINA

INDIA

MALAYSIA

TAIWAN

THAILAND

VIETNAM

Figure 2 Farmed production ofMacrobrachium rosenbergii (the FAOdata include the categories giant riverprawn, freshwater shrimps/prawnsnei and freshwater crustaceans nei)in major producing countries in Asiain 2001 (mt) (FAO 2003).

0

50000

100000

150000

200000

250000

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

CHINA OTHER ASIAN TOTAL REGION

Figure 3 Trends in farmed Macro-brachium rosenbergii (the FAO datainclude the categories giant riverprawn, freshwater shrimps/prawnsnei and freshwater crustaceans nei)production in Asia (mt) (FAO 2003).

Overviewof freshwater prawn culture in USA MBNew Aquaculture Research, 2005, 36, 210^230

212 r 2005 Blackwell Publishing Ltd, Aquaculture Research, 36, 210^230

production is still quite small. A newcomer is theRussian Federation, where this species is grownmainly in the heated e¥uent from electric powergeneration.

Rate of global expansion

It is di⁄cult tomeasure the rate of expansionof fresh-water prawn farming, because of the lack of statistics

0

140,000

120,000

100,000

80,000

60,000

40,000

20,000

M. nipponense (estimate from Miao Weimin 2003)M. rosenbergii (FAO 2003) M. nipponense (estimate from Wang & Qianhong 1999)

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001Figure 4 Chinese farmed production ofMacrobrachium nipponense is catching upwith M. rosenbergi (the FAO data includethe categories giant river prawn, fresh-water shrimps/prawns nei and freshwatercrustaceans nei) (mt).

10

20

30

40

50

60

70

0

COSTA RIC

A

DOMNICA

DOIMIN

ICAN R

EP

EL SALVADOR

GRENADA

GUADELOUPE

GUATEMALA

HONDURAS

JAMAIC

A

MARTINIQ

UE

MEXICO

PANAMA

PUERTO RIC

O

ST. LUCIA

SURINAME

USA

Figure 5 Production of farmedMacrobrachium rosenbergii (the FAOdata include the categories giant riverprawn, freshwater shrimps/prawnsnei and freshwater crustaceans nei)in Central and North America in2001 (mt) (FAO 2003).

0

100

200

300

400

500

600

700

800

900

BRAZIL ECUADOR FRENCH GUIANA PERU

Figure 6 Production of farmedMacrobrachium rosenbergii (the FAOdata include the categories giantriver prawn, freshwater shrimps/prawns nei and freshwater crusta-ceans nei) in major producing coun-tries in South America in 2001 (mt)(FAO 2003) (Note: FAO data for Brazilhas been divided by a factor of ten(see text)).



about the culture of M. nipponense in China. How-ever, if we assume that the estimates for that speciesthat have been cited earlier are reasonably accurate,we can deduce that over 330000mt of all speciesof Macrobrachium were raised through aquaculturein the year 2001 (Fig. 8). No doubt there has beenfurther expansion since that time. The average an-nual expansion rate (APR) of freshwater prawn farm-ing, if all FAO data and the estimates for M.nipponense are combined, between 1992 and 2001was over 29%. Between1999 and 2001, the global ex-pansion rate was even more rapid (48%). However,nearly 83% of the expansion during that whole dec-ade and over 85%of the expansionbetween1999 and2001occurred because of the meteoric rise in the re-ported farmed production of M. rosenbergii and theestimated output ofM. nipponense in China. In parti-cular, the estimated productionofM. nipponense indi-cates an APR of nearly 183% year�1 between 1999

and 2001; in other words, production appears to begoing up by a factor of over 2.8 annually, a very ex-ceptional rate! This shows that, as in the case ofmany other farmed food¢sh species, the inclusion ofChinese data distorts the analysis of trends in the restof the world. So let us look at the picture after remov-ing the data from China.Without Chinese data, theAPR in the rest of the world over the decade 1992^2001 was a more modest 11%. However, the expan-sion rate seems to be increasing: in the 2 years from1999 to 2001it was over 20%.So far, in calculating APR, I have included the FAO

categories ‘freshwater crustaceans nei’ and ‘fresh-water prawns/shrimps nei’ in the ‘all species’ cate-gories. The main e¡ect of this is to add the largeestimated production of ‘freshwater crustaceans nei’in Viet Nam. This category, which is believed toconsist principally of M. rosenbergii, contributed12000mt in1992, over 25000mt in1999 and about

0

10

20

30

40

50

60

FIJI I

SLANDS

FRENCH POLYNESIA

GUAM

MAURITIU

S

NEW C

ALEDONIA

RUSSIAN F

ED

RÉUNION

SENEGAL

SOLOMON ISLANDS

ZIMBABW

E

Figure 7 Minor production offarmed Macrobrachium rosenbergii(the FAO data include the cate-gories giant river prawn, fresh-water shrimps/prawns nei andfreshwater crustaceans nei) inother areas in 2001 (mt) (FAO2003).

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

FAO DATA (for M.rosenbergii, f/w prawnsnei, & f/w crustaceansnei)

ESTIMATES FOR M.nipponense (2000 figurecalculated from APR1999-2001)TOTAL F/W PRAWNS

Figure 8 Estimated expansion offreshwater prawn farming 1992^2001 (mt).



28000mt fromViet Nam to the global all-species ¢g-ure for 2001, for example. If we exclude these miscel-laneous (‘nei’) categories and simply look at the FAOdata for M. rosenbergii alone, the global expansionratewas over 27% year�1over the decade1992^2001.If data from China is excluded, the production

of M. rosenbergii alone still expanded by nearly12% year�1 in the rest of the world in the decade1992^2001 and increased considerably beyond thedecadal average, to over 30% year�1 in 1999^2001.The rapid increase in the expansion ofM. rosenbergiifarming outside China is due mainly to massive ex-pansion in India and a resurgence of production inone of the pioneering countries, Thailand. Between1999 and 2001, the production of M. rosenbergii in-creased at an annual rate of 86% in India and over19% inThailand.The current production of freshwater prawns is

still relatively small, compared with the scale of mar-ine shrimp farming. However, marine shrimp farm-ing has not been expanding so rapidly as is shown inFig. 9, that has been prepared from FAO data (FAO2003) and includes the two categories ‘freshwaterprawns, shrimps nei’ and ‘freshwater crustaceans‘nei’, but therefore excludes the uno⁄cial estimatesofM. nipponense production.The top line of each pairincludes Chinese production; the bottom of each pairexcludes China. In this ¢gure, the trends for marineshrimpand freshwater prawns look similar. However,if you calculate the annual average growth rates, itbecomes clear that freshwater prawn farming hasbeen expanding at a much faster rate than marineshrimp, whether China is included or not. Globally,the APR for the decade was 27.4 per year for fresh-water prawns but only 3.9% year�1 for marineshrimp. Excluding China, the APRs for the rest of

the world were 11.8% year�1 for freshwater prawnsand 3.8% year�1 for marine shrimp.

Recently published news andresearch results

The literature up to the year 2000 was reviewed byNewandValenti (2000). Since that time I have endea-voured to keep up with the research work that hasbeen published in international journals and thenews about research results and farming practicesin various magazines. I have tried to summarizethis information in the next two sub-sections of thispaper.

News of general interest, 2000^2003

Bangladesh

In 2000, Ahmed (2000) reported that 8306 ha werebeing used forMacrobrachium culture in Bangladesh,usingwild fry, but ACC (2003) reported that the grow-out area has risen to 40000ha. Nandeesha (2001)reported that over 100000 small farmers earn mostof their livelihood from culturing freshwater prawns;however, they still depended on the availability ofwild seed. Some farmers were reported to be stockingwild tiger shrimp (P. monodon) with wild Macrobra-chium. Penaeus monodon has been grown in low sali-nities in Thailand and in freshwater in India.However, the dangers of this practice have been iden-ti¢ed (Fegan 2002).Ahmed (2000) reported that freshwater snails

were the food of choice by farmers in Bangladesh,although that may now have changed.

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,000

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Marine shrimp Marine shrimp (no China)

M. rosenbergii M. rosenbergii (no China)

Figure 9 Trend in the farmed pro-duction of Macrobrachium rosenbergii,comparedwith the total for all speciesof marine shrimp (FAO 2003).



Brazil

Moraes-Riodades and Valenti (2001) see a future forthe intensive production of M. rosenbergii by largercompanies for domestic and export markets andsmall-scale family units (for local use) in theAmazo-nia region of Brazil. Small-scale family farms couldrear this species, as well as the indigenous (andmuchsought after) M. amazonicum using more extensivetechnologies for local consumption.

China

In China, the province of Hainan is reported to be im-porting an improved breed ofM. rosenbergii from theCharoen Pokphand hatcheries in Thailand (Anon-ymous 2001d). CP claims that whereas a 30-g aver-age size is normally achieved, their ‘CPF giantfreshwater shrimp’ grow to an average of 100 g formales and 60 g for females (Anonymous 2001e) aswell as having a 60% meat content (Anonymous2001f). China is researching M. malcolmsonii as apossible replacement for M. rosenbergii (Anonymous2002d). Macrobrachium malcolmsonii is said to growfaster than the currently cultured freshwater prawnspecies in China and is expected to become popularwith consumers. The broodstock was introducedfrom Sri Lanka. An up-to-date review of freshwaterprawn farming in China is being presented by MiaoWeimin in this symposium, so I will not commenton his earlier published paper (Miao & Ge 2002).

Ghana

The Institute of Aquaculture (Stirling University, Stir-ling, UK) is working with M. vollenhovenii in an at-tempt to encourage the farming of this species inGhana, where it is indigenous and the subject of arti-sanal activity in roadside markets (Brown 2001).

India

In the last 3 years, many articles on Macrobrachiumfarming in India have appeared in international ma-gazines; only a few are sampled in this paper, since Iam sure that we will hear much more up-to-date in-formation here during our symposium this week.Simple guidelines for freshwater prawn farmingin India have been prepared by Saxena (2003). Ithas been reported that Andhra Pradesh produces27000mt of M. rosenbergii; according to MPEDA,this output could be doubled in 2 or 3 years if farmerstake up this type of farming (Anonymous 2003a).Thegovernment of Haryana was reported to be wishing

to encourage freshwater prawn farming, using in-puts and technology from Tamil Nadu (Anonymous2001c). An earlier phase of the boom in freshwaterprawn farming in India, mainly in the coastal pro-vinces of Tamil Nadu and Andhra Pradesh, was de-scribed by Fegan and Sriram (2001), who reportedthat it was more pro¢table than sugarcane or riceproduction. However, they warned that better pro-duction e⁄ciency and marketing would be essentialas the total production increases and farm-gateprices drop. Jain and Diwan (2002) stated thatM. ro-senbergii can be cultured in waters of 15 g L�1 and istherefore a suitable species for culture in saline was-telands in India; they also suggested considering M.malcolmsonii,M. idella andM. lamarrei. Commentingthat productivity was still quite low in India (an aver-age of 600 kg ha�1 in the year to March 2002),Merican and Vasudevan (2003) noted that about1.2million ha was available and only about 13% hadbeen used to date. These authors forecast that Indianproduction of Macrobrachium would rise by about30% per year over the next 2 or 3 years.Two articles by Reddy and Rao (2001a, b) provided

a summary of farming practices in India and con-cluded that freshwater prawn farming was poisedfor rapid expansion; however, this potential wasbeing compromised by the high cost of postlarvae(PL) (at that time Rs. 0.75^0.9 each, up to three timesgreater than PL of P. monodon). Another summary ofthe expansion of freshwater prawn farming in Indiawas provided by Nagarajan and Chandrasekar(2002); a typical cost/income scenario was providedfor a farm in Andhra Pradesh, which showed an op-erating pro¢t of over US$ 1000 ha�1crop�1. Theseauthors reported a lack of export demand in 2002and government restraints on the expansion of theindustry because of concerns about the excessiveuse of groundwater, the potential salinization of agri-cultural land and the conversion of paddy ¢elds toprawn farms. Nandeesha (2003) reported that thepolyculture of freshwater prawns with carps has al-most entirely been replaced by prawn monoculture.He reported that about 22000ha of ponds were de-voted to freshwater prawn culture in the Nellore dis-trict of Andhra Pradesh alone. Although hatcheryraised seed is nowavailable, their quality is variable.Selvaraj and Kumar (2003) predicted that fresh-

water prawn production in India could increase to50000mt year�1 by 2010. Several established fresh-water prawn farmers and hatchery operators in An-dhra Pradesh and Tamil Nadu have been promotingand assisting similar development in other Indian



States (Nandeesha 2003; J. Susheela, pers. comm.2004). In a conference held here in Kochi in 2001,a farm-made aquafeed mill in Kuttanad was an-nounced; the freshwater prawn feed produced wassaid tohave reduced feeding costs by 38%and resultedin less non-marketable size animals (Anonymous2000, 2001a). Merican and Vasudevan (2003) statedthat local feed companies in India devoted about10^15% of their production capacity to feeds for fresh-water prawns. Feed production for crustacea is domi-nated by CP,Waterbase, Avanti and Higashimaru. Inaddition there is Hanaqua, Grobest, Godrej and 15smaller companies but it was not clear if all these com-panies manufacture freshwater prawn feeds.

Jamaica

Macrobrachium farming is proving quite popular inJamaica where it is grown in polyculture with tilapia(Aiken, Morris, Hanley & Manning 2002).

Malaysia

Macrobrachium rosenbergii is said to be increasinglypopular among consumers of all races in Malaysia(Anonymous 2001i).

Philippines

Following 70% survival rates in the (government)hatchery phase, batches of freshwater prawn PL arebeing distributed to the private sector in the Philip-pines; polyculture with tilapia is being favoured(Anonymous 2001g). Macrobrachium rosenbergii waseven being promoted for culture in metal drums inurban areas (Anonymous 2001h).

Paci¢c

Freshwater prawnswere included in the eight speciesselected as having the most potential for culture inthe Paci¢c region (Anonymous 2002a).

Russia

Freshwater prawns are being produced in one farmin Russia, which produced 6mt in 2000. Most is soldin Moscow but some in the location of the farm, As-trakhan (Anonymous 2001b); investment was beingsought to enlarge capacity.

Thailand

CP was said to be planning a major expansion infreshwater prawn production in Thailand (Anon-

ymous 2001e).The e¡ect of this programmemay ulti-mately ¢lter through to the FAO production statistics.

Viet Nam

Typically, Macrobrachium have been reared in con-junction with rice production inViet Nam, based onwild fryand little or no feed, achieving low productiv-ity (150^300 kg ha�1crop�1). Now hatchery raisedPL are more available, many farmers in the MekongDelta are using both fresh ¢sh and arti¢cial feedsfor 6-month culture periods (leaving another6 months for two crops of rice) to achieve1000^1500 kg ha�1crop�1 (Ridmontri 2002). Allmajor seafood processors in the Mekong Delta andsome feed companies have become involved inhatchery and feed supply for freshwater prawn farm-ing, and see processed prawns as an importantexport item. In this country, Proconco is developinga feed for freshwater prawns and plans to train farm-ers to run simple hatcheries through its extensionwork (Buranakanonda 2001).

Miscellaneous news

A number of other items of general news were pub-lished during the period. These included the reportthat freshwater prawns are being considered as acandidate species for an organic label in Asia (INFO-FISH 2002). Interest in farming other species hasbeen reported. Nandeesha (2003) reported that therewas commercial potential in rearingM.malcolmsoniiin both India and China. Moraes-Riodades andValen-ti (2001) also see a future for the culture ofM. amazo-nicum in theAmazonia region of Brazil.

News of scienti¢c and research importance,2000^2003

Biology

A useful book for the shelves of taxonomists on thebiology of palaemonid prawns has been provided byJayachandaran (2001) and reviewed by New (2002b).One hundred and forty-four pages are devoted toMacrobrachium spp. More than 180 valid species arenow recognized, far more than the 125 species men-tioned by Holthuis (1980). Another useful book is onthe biology of decapod larvae (Anger 2001).

Breeding, genetics and sex reversal

Research work on the breeding, genetics and sex re-versal of Macrobrachium spp. in the past 3 years has



been active. In a recent review article on the geneticimprovement of freshwater prawns, whose publishedreference list is unfortunately incomplete, Lutz(2003) states that spermatophore microinjection ap-pears to be aviable means of introducing genetic con-structs into Macrobrachium species. Gene transfermay therefore complement the promise of ‘conven-tional’ selection and hybridization as a means of im-proving performance in freshwater prawn culture.According to this author, the most important traitsthat might be improved are, in addition to growthrate, cold tolerance, the duration of larval develop-ment and the tolerance of reduced salinity duringthe larval cycle. An Indo-Norwegian consultation inMumbai in 2001identi¢ed the need for collaborationbetween Indian national research institutions andAKVAFORSK on the genetic improvement of fresh-water prawns (Anonymous 2002b). It would be inter-esting to hear if this collaboration has commenced.Baghel and Saxena (2001) proposed a number of

biotechnological tools to enhance freshwater prawnproduction. These included chromosomal engineer-ing, molecular genetics, genetic engineering and tis-sue culture engineering. Noting that freshwaterprawns were less susceptible to the white spot syn-drome virus than marine shrimp, these authors be-lieve that gene transfer should be used to producestrains having a growth hormone gene construct.Sterile M. rosenbergii can be produced when juve-

niles are irradiated at 1.0 and 1.5 krad using g radia-tion from cobalt-60 (Lee & Tiersch 2001).Whenadult,these irradiated females did not produce eggs, or pro-duced less than100 eggs that were dropped within 4days. Irradiated males were shown to produce no, orreduced sperm, and failed to fertilize the eggs of non-irradiated females.Buranakanonda (2002) reported that there were

three major strains (one a cross-bred strain) of fresh-water prawns inThailand and that Kasetsart Univer-sity had found that the Myanmar prawns from theYapil River were the meatiest. This university has in-stituted a breeding programme, using this strain toselect for good fecundity and survival, as well assmaller claws and heads. I believe that it is possiblethat this work has been done in conjunctionwith CP(see earlier).Bart and Yen (2001) reported that PL survival (up

to 36 days) was much higher (33%) when broodstockM. rosenbergii from Thailand were used instead ofthose fromViet Nam (o2%). Furthermore, cross bredThai females andViet Nammales resulted in an evenhigher PL survival (39%).This work indicates the im-

portance of comparative work on the various strainsof freshwater prawns, and the potential improvementthat could be gained not only from selection andcross breeding but also, perhaps, from examiningwhether di¡erent strains have di¡erent rearing re-quirements.Working with M. australiense, Dimmock,William-

son and Mather (2002) have found that there is asmuch trait variation within geographical regions asbetween di¡erent regions. This variation seems to berelated to environmental factors (e.g. abdomen sizecorrelates with increased habitat structure). Manipu-lating temperature reinforces environmental in£u-ences on morphology in this species. Breeding work(perhaps with otherMacrobrachium spp. also) shouldtake local habitat characteristics into consideration.Chinese scientists have successfullycrossed female

M. nipponensewith maleM. hainanense (Anonymous2002c; H. Fu, pers. comm. 2002). Isozyme analysiscon¢rmed that the hybrids possessed both maternaland paternal genes. Of the ¢ve single pair crosses,four spawned and three hatched hybrids (the otheraborted). The hatching rate of the hybrids was over90% and the survival rate to PLwas 20^60%.In a study providing preliminary information for

those seeking to produce hybrids, Graziani, De Dona-to, Lodeiros, Orta and Salazar (2001) found that, ofthe four species considered, the closest genetic dis-tances were between M. carcinus and M. rosenbergiiand the most genetically distinct wereM. acanthurusand M. amazonicum. Leucilaminopeptidase (LAP)and Peptidase II (PEPII) can be used to detect the pre-sence of hybrids among these species.Several institutes in Israel, Thailand and the UK

are working with sex-reversed prawns (Anonymous2000^2001; Brown 2001, 2002; Buranakanonda2002) but I have not yet seen any peer-reviewed pub-lication on their results.Cavalli, Lavens and Sorgeloos (2001) showed that

under proper rearing conditions, M. rosenbergii fe-males are able to spawn up to ¢ve times within a180-day period, compared with three to ¢ve times asreported for wild populations. Indicating that thenumber of viable larvae produced might be increasedby in vitro incubation, these authors discuss the con-straints to this technique; disinfecting the eggs maybe necessary to replace the loss of the anti-microbialsecretions of the incubating female.It is well known that increasing the salinity that

adult females are kept in enhances hatchability; com-monly they are kept at 5 g L�1. Recently Cheng, Liu,Cheng and Chen (2003) have shown that both male



and female adult prawns (M. rosenbergii) can adapt toa salinity of 14 g L�1within 2 days. Since this is thecommonly used salinity for rearing larvae of thisspecies, this ¢nding could simplify hatchery opera-tion. Law,Wong and Abol-Muna¢ (2002) found thatM. rosenbergii egg hatchability is extremely sensitiveto hydrogen ion concentration in brackish water. At12 g L�1, the highest hatching rate (92.22%) was de-tected at pH 7.0. However, at pH 6.5 and 7.5, hatchingrates markedly fell to 5.00% and13.33% respectively.Hatching rates at pH 5.0, 8.0, 9.0 and 10.0 were zero.This important study indicates that careful controlof the pH of the brackish water used to hatch M. ro-senbergiiwould increase hatching success, reduce thenumber of broodstock needed and (perhaps most im-portantly) reduce hatchery production costs. It is notyet known whether other species of Macrobrachiumare so sensitive to pH at the time of hatching.The availability of cryopreserved larvae could

greatly assist in facilitating stock distribution wherelack of hatchery-reared animals hampers the expan-sion of freshwater prawn farming. Pillai, Rao andMohanty (2001) measured the toxicity of variouscryoprotectants ^ dimethyl sulphoxide (DMSO),methanol, glycerol and ethylene glycol ^ on the ¢rstzoeal stages ofM. rosenbergii. Methanol was found tobe the most toxic, followed by DMSO. Larvae could besafely exposed to these cryoprotectants for 20min at20 1C at up to 10% v/v. Multiple cryoprotectants (amixture of these substances) were found to be lesstoxic than single substances.

Diseases, prophylaxis and the use ofimmunostimulants

Several papers on the diseases of freshwater prawns,on prophylaxis, and the use of immunostimulantshave been published. In a study over a larval rearingcycle of M. rosenbergii by Phatarpekar, Kenkre, Sree-pada, Desai and Achuthankutty (2002), the bacterial£ora was predominantly Gram-negative (75% of thetotal isolated strains). Aeromonas, Alcaligenes andPseudomonaswere the most frequently observed gen-era in the water but Alcaligenes, Enterobacteriacae,Pseudomonas and Streptococcus were the most abun-dant on the larvae themselves.Vibrio spp. were foundin eggs and water but were completely absent in lar-vae. The bacterial £ora of eggs resembled the waterbut a distinctly di¡erent population was associatedwith the larvae.Nagarajan and Chandrasekar (2002) reported

some of the common problems encountered in the

rearing of freshwater prawns in India and the treat-ment used to counter them. The problems includedwhitemuscle or idiopathicmuscle necrosis, ciliate in-festations, antenna and tail rot, soft shell, hard shelland low dissolved oxygen.Cheng and Chen (2002) found that M. rosenbergii

(size not stated) reared at high temperatures (33^34 1C), high pH (9.0^9.5), low pH (4.6^5.0), low DO2

(1.75^2.75mg L�1) and exposed to ammonia-N(0.55mg L�1) and copper sulphate (0.2mg L�1) ex-perienced a decrease in phenoloxidase activity, lead-ing to a reduction in their immune response andsusceptibility to Lactococcus garvieae infection. Thispathogen, together with the yeast-like Debaryomyceshansenii and Metschnikowia bicuspidata, has causedmany disease outbreaks inTaiwan.Cheng and colleagues (2003) noted that experi-

mental challenge of freshwater prawns by the injec-tion of bacteria and subsquent exposure to di¡erentsalinity levels has shown that 5 and10 g L�1appearsto have a favourable e¡ect on survival; Taiwanesefarmers are therefore likely to add brine to grow-outponds.Goswami and Prasad (2000) have found that ben-

zalkonium chloride (BKC) can be used as an e¡ectiveanti-bacterial and immunostimulant forM. rosenber-gii. These authors reported that the minimum lethalconcentration for the several bacteria tested rangedfrom 1.0 to 1.5 ppm. Despite the fact that Liao andGuo (1990) had reported that the tolerance to BKC ofthis species was 2 ppm in 24 h, Goswami and Prasad(2000) found the 24-h LD50 for 2-month oldM. rosen-bergii (weight not indicated) to be10 ppm. Some cau-tion in its use seems to be indicated until furtherstudies are reported.The Taura Syndrome (TSV-like) virus that is com-

mon in P. vannamei has not been found in freshwaterprawns (Anonymous 2003b).

Experimental techniques

A development in experimental technique has beennoted. The Institute of Aquaculture (Stirling Univer-sity, Stirling, UK) has shown that it is possible notonly to tag the very smallest PL M. rosenbergii butalso pre-metamorphic larvae (Anonymous 2000^2001). Describing this technique in detail, Brown,McCauley, Ross, Taylor and Huntingford (2003) con-cluded that VI elastomer tags (a coloured liquid thatcures to a £exible solid after injection under the epi-dermis and £uoresces under UV light) could be used



to mark small numbers of individual larval and im-mediately PL prawns and that VI alphanumeric tags(small biocompatible plastic labels with unique codesthat are inserted beneath transparent regions of skin)could be used tomarkanunlimited number of indivi-duals with a size of approximately 0.5 g.

Management, including the use of substrates

Several papers onnurseryand grow-outmanagementhave been published. Marques, Lombardi and Boock(2000) found that high-density nursery culture(either 10 PL L�1 for a primary phase using 0.011gearly metamorphosed animals, or 800 PLm�2 in asecondary phase stocking the results of the primaryphase as 0.053 g PL) of M. rosenbergii in cages withinan earthen pond seems feasible as a means of redu-cing nursery phase costs.Van Arnum,Tidwell, Coyle,Vitatoe and McCathy (2001) reported that, under in-door nursery conditions, 0.04 g PL M. rosenbergiistocked at 430 PLm�2 had a signi¢cantly better sur-vival rate (76% over 60 days) with continuous light(L24:D0) than with either L12:D12 (59%) or L0:D24(58%). No comment on the light intensity or its spec-tral quality was mentioned in this abstract.Ranjeet and Kurup (2002a), in a paper on hetero-

genous individual growth (HIG) mentioned the pos-sibility that di¡erential growth could have a geneticbasis. The work of Sun,Weatherby, Dunlap, Arakaki,Zacarias and Malecha (2000) indicates that there aresubstantial di¡erences in the androgenic gland (AG)protein content, SDS-PAGE polypeptide pro¢le andcellular morphology between the OC, OBC and BCmale morphotypes of M. rosenbergii; this ¢ndingmay be a further indication that HIG has genetic aswell as social associations. For the moment, however,Ranjeet and Kurup (2002a) have stressed the impor-tance of careful grow-out management in commer-cial farms to maximize the yield of marketableprawns and synchronize their availability with mar-ket requirements. An excellent review on the man-agement of size review has been provided byKarplus, Malecha and Sagi (2000). Ranjeet and Kur-up (2002b) found that the trend forM. rosenbergii lar-vae that hatch ¢rst to be weaker and take longer toreach metamorphosis appeared to continue into thegrow-out phase. However, these ¢ndings are in con-trast to the results of Zacarias (1986) as reviewed byKarplus and colleagues (2000). Using geneticallymarked populations, Zacarias (1986) showed thatearly-hatching larvae are likely to become early-set-tling PL, which, in turn are likely to become larger

juveniles. Further research on this topic is necessarybefore pre-stocking batch-grading can be truly e¡ec-tive in maximizing production and revenue fromfreshwater prawn farming.According to D’Abramo, Daniels, Gerard, Jun and

Summerlin (2000), strategies that avoid achieving thecritical standingcrop that induceswhat is apparentlyachemical-mediated growth reduction are necessary.These could include selective harvesting or stock ma-nipulation and movement. These authors were alsoable to demonstrate an important feature of immediatebene¢t to commercial culture in special marketingconditions suchas the temperate-zone culture of fresh-water prawns ^ a density threshold that could be usedto reduce growth rates and therefore adjust productionto suit the best time for marketing. Reductions inweight gain began to occur when a critical biomassdensity of approximately 500mgL�1was attained.Alston and Garc|¤ a-Pe¤ rez (2001), studying the poly-

culture of tilapia stocked at 1m�2 and freshwaterprawns at 5m�2, found that removing all femaleprawns during each monthly partial harvest over a19-month period increased the numbers of market-able prawns but did not a¡ect meanweight (40 g).Research on the use of substrates to increase pro-

duction in freshwater prawn grow-out systems hascontinued in the USA and is beginning to be appliedin small-scale commercial practice. Tidwell and hisco-workers in Kentuckyhave published a series of pa-pers (Tidwell, Coyle, Van Arnum & Weibel 2000a;Tidwell, Coyle,Van Arnum,Weibel & D’Abramo 2001;Tidwell, Coyle,Van Arnum &Weibel 2002) on the useof substrates consisting of 120-cm-wide panels ofpolyethylene ‘construction safety fencing’ material,placed in rearing ponds either horizontally or verti-cally to increase the surface area available to prawns.This material is illustrated in Tidwell and D’Abramo(2000) and New (2002a). In one of their most recentpapers,Tidwell and colleagures (2002) reported thatthey had obtained a signi¢cantly increased produc-tion rate of freshwater prawns (2653 kg ha�1) whenthe surface area was increased by 100% comparedwith a control with no substrate (2140 kg ha�1) inan experiment lasting106 days where 0.2-g juvenileswere stocked at 65000ha�1. Higher average ¢nalweights were obtained when substrates were used.An intermediate production level between these ex-tremes was achieved with half the quantity of addi-tional substrate but, at this level, it made nodi¡erence whether the substrate was hung verticallyor horizontally.Vertically hung substrates are easierto install and maintain and o¡er the possibility of



increasing surface area even more than 100%, andtherefore the potential of greater production.On the other hand, Posadas, Walters and Long

(2003), reporting a 120-day experiment where sur-face area was increased over no-substrate controlsby 100%, using similar vertical substrates and juve-niles stocked at 50630 ha�1, found no signi¢cante¡ect on survival rate, harvest size or count, yieldor feed conversion. However, the average yield(1497 kg ha�1) obtained by Posadas and colleagues(2003) was markedly lower than those achievedby Tidwell and colleagues (2002). More detailedcomparison between these two experiments is neces-sary, to see what experimental parameters di¡ered,before further research con¢rms the obvious ad-vantages that Tidwell and colleagues (2002) havefound in adding substrates to freshwater rearingponds.D’Abramo and colleagues (2000), studying the ef-

fects of combinations of water volume, bottom surfacearea and water replacement rate onweight gain of ju-venile M. rosenbergii, have highlighted the impor-tance of allowing for maximum density-independentgrowth of animals for all treatments in experimentalwork with crustaceans that uses growth as a re-sponse variable to compare performance on di¡erentdiets. Greater weight gain was achieved under bothgreater water volume and bottom surface area. In-creased water replacement did not compensate forlowerwater volume. Increasing available surface areamakes it possible to reduce the water replacementrate. This work is therefore important for moving to-wards zero-exchange grow-out systems.Vitatoe, Tidwell, Coyle and Van Arnum (2000) re-

ported that menhaden ¢sh oil could be used as a suc-cessful alternative to petroleum products such as oiland diesel fuel for eliminating the air-breathing in-sects that predate on small, newly stocked freshwaterprawn juveniles. Not only does this promote environ-mental safety and comply with organic certi¢cationbut it eliminates the possibility that juvenile prawnsmay consume toxic petroleum droplets after stock-ing. These workers stated that menhaden ¢sh oilapplied at 1.6 gallons (US) per surface acre( � 15 L ha�1) was not only e¡ective in controllingair-breathing insects but also cost-e¡ective in com-parisonwith petroleum-based products.

Nutrition and feeding

Besides genetics, the major area of research publica-tion on Macrobrachium in the past 3 years has been

on nutrition and feeding. Coyle and Tidwell (2002)suggested that more research should be carried outon management practices that maximize the avail-ability of natural food. ‘Phase feeding’, where dietswith increasing protein levels are applied during theproduction cycles were suggested; the use of a lowprotein ‘fertilizer’diet for the ¢rst month, followed bya 28% protein steam pelleted diet for the next 6weeks and a 40% protein diet for the ¢nal 4 weeks ofrearingwere used in one trial.This is contrary to nor-mal practice (lowering protein levels as animalsbecome older) but was suggested as a means ofproviding more and better nutrition when naturalfoods become grazed down. Further trials describedby Coyle and Tidwell (2003) compared phase feedingwith the use of a 32% diet (similar to a cat¢sh feedformulation) throughout the rearing cycle. No di¡er-ences in total production or average prawn weightwere observed; however, phase feeding resulted in a20% increase in the number of animals weighingover 30 g. In each trial feeding rates were 20% higherthan normal and stocking densities were relativelyhigh (6.5 and 7.9m�2). Phase feeding using amarineshrimp diet also increased feeding costs, so carefuleconomic and marketing considerations need to bemade in applying such research ¢ndings.Correia, Pereira, Silva, Horowitz and Horowitz

(2003) found that increasing the natural productivityof ponds signi¢cantly improves feed conversion ratio,with concomitant savings in farm operating costs.Fertilization made it possible to reduce feeding ratesby up to 50% with no reduction in yield. In this case,the authors used an average of 2.5 kg of lime,110 g ofsimple superphosphate and 340 g of ammonium sul-phate per 50m2 pond every 2 weeks (in practice, ap-plication rates were adjusted on the basis of water-quality analysis) during an 84-day trial. Full feedingwas compared with a reduction of 50% throughoutthe trial and a treatment that consisted of feeding0%, 25% and 50% of the control feed for the threesubsequent periods of 28 days. The latter treatmentresulted in prawns that were smaller than marketsize and a much reduced total net yield. However, areduction of 50% in feeding rate gave similar ¢nalweights and yield.A successful semi-synthetic broodstock diet (44%

protein,9% lipid) forM. rosenbergiiwas used in repro-ductive performance trials by Cavalli and colleagues(2001). The formulation included, inter alia, casein,lobster meal, soy protein isolate, squid meal, shrimpmeal, crab meal, synthetic amino acids, soybean oil,¢sh oil, a protein extract attractant, astaxanthin, soy



lecithin, vitamins and minerals, together with a car-rageenan binder and anti-oxidants.Roustaian, Kamaruddin, Omar, Saad and Ahmad

(2001) have demonstrated the importance of lipid asthe major metabolic energy source for growing lar-vae ofM. rosenbergii and postulated that research onthe e¡ects of the lipid compositionof broodstock dietswould be bene¢cial. Roustaian, Kamaruddin, Omar,Saad and Ahmad (2000) found that the amino acidcomposition of M. rosenbergii larvae appeared to berelatively unchanged during larval stages I^IX, sug-gesting that their dietary amino acid requirementscould be satis¢ed by a feed having a similar aminoacid pro¢le to the larvae themselves. D’Abramo(2002) reported the successful development of a for-mulated microbound feed to replace the use of Arte-mia for larval stages V^XI and for PL M. rosenbergii.The formulated diet was moist (60% moisture) andcould not be reduced to particles below 0.25mm un-less previously dried.The diet was energy dense (46%proteinand 37% lipid). Although experimentally suc-cessful, as far as I know its use under commercialhatchery conditions has not yet been reported; itsunit cost was also not stated in this paper.Niu, Lee, Goshima and Nakao (2003) found that

the food consumption of M. rosenbergii PL distinctlyincreases with temperature (23^33 1C) and is posi-tively related to initial bodyweight (7^38mg). Modelswere constructed to relate maximum food consump-tion and speci¢c growth rate withwater temperatureand initial size; these could be used to predict thefood requirements and growth of PL in aquaculture.In an experiment where a series of diets contain-

ing varying amounts of trash ¢sh meal and ground-nut oil cake with level amounts of shrimp head mealand coconut oil cake were fed to 0.27 g initial weightM. rosenbergii and reared for 30 days, Hari and Kurup(2003) found that highest growth rate andmaximumprotein utilization was obtained with a 30% proteinlevel. In a subsequent experiment using four dietswith this protein level, these authors showed that itwas possible to achieve similar results as trash ¢shmeal was gradually replaced by groundnut oil cake,thus indicating the potential for dietary cost savings.Posadas, Walters and Long (2001) and Posadas,

Walters and Long (2002) compared di¡erent feedsand feeding regimes for the grow-out of M. rosenber-gii in Mississippi. A daily ration of cottonseed (ap-proximately 3.7 kg ha�1) was applied to all fourtreatments for the ¢rst 30 days of rearing. In the con-trol ponds, a sinking pelletized 32% protein cat¢shfeed was fed from day 31 for the next 90 days to

harvest. In the second series of ponds, the pelletizedcat¢sh feed was applied for the second 30 days ofrearing, followed by an extruded 35% protein cat¢shfeed for the ¢nal 60 days. The third series of pondswas treated similarly during the second 30-day peri-od but an extruded 40% protein sinking marineshrimp feed was used for the ¢nal 60 days. Finally, inthe fourth series of ponds, a 35% protein marineshrimp feed was applied from day 31 for the next 90days. Althoughyields were not signi¢cantly di¡erent,the highest (1183 kg ha�1) was achieved by the con-trol (sinking 32% cat¢sh feed from day 31to harvest).The authors concluded that dietary protein level hadno appreciable e¡ect on yield, survival, feed conver-sion or ¢nal average prawn count (about 22 kg�1).However, FCR in all treatments was rather poor(3.0^4.1:1). No information on the analysis of the var-ious feeds was presented; thus, no comparison of theprotein/energy ratios was feasible. It is possible thatthe dietary protein levels of all treatments in this trialwere unnecessarily high. D’Abramo and New (2000)reported the use of commercial freshwater prawnsfeeds with protein levels ranging from 22% to 38.5%and that, where natural food was also available, sev-eral trials have reported success with diets havingprotein levels as lowas13% or14%.Ali and Sahu (2002) found that the use of fermen-

ted ¢sh silage as a feed ingredient showed better (butnot statistically signi¢cant) weight gain, FCR andPER than freshwater prawns fed 35% protein/8% li-pid diets containing ¢sh meal or acid ¢sh silage.GonzaŁ lez-Pen� a, Gomes andMoreira (2002) showed

that the speci¢c growth rates, feed e⁄ciency conver-sion and protein e⁄ciency ratios of small and largeadultM. rosenbergii improved as levels of dietary ¢brewere increased (substituting cellulose for starch insemi-puri¢ed diets) from 0.4% to 8%; they concludedthat the inclusion of up to 10% of dietary ¢bre in-creases growth rates in adult prawns by increasingnutrient residence time, thus increasing absorption.Mendoza, Montemayor, Aguilera,Verde and Rodr|¤ -

guez (2001) found signi¢cant attractive propertieswhen arginine, cadaverine, freeze-dried red crab ex-tract and coconut extracts were added to a commer-cial diet for M. rosenbergii. Research has shown thatanti-nutritional tannins a¡ect M. rosenbergii far lessthan ¢sh (Anonymous1999^2000).Using ascorbyl 2 polyphosphate, Hari and Kurup

(2002) found that dietary vitamin C levels have a per-ceptible in£uence on the survival of M. rosenbergiijuveniles and recommended an inclusion rate of135mg kg�1of ascorbic acid equivalent.



Available surface area can be increased by introdu-cing arti¢cial substrates, as shown by the continuingwork of Tidwell and colleagues (2000a, 2001, 2002).The latter authors have demonstrated that increasingsubstrate increases production and improves feed ef-¢ciency.

Polyculture

The polyculture of freshwater prawnswith other spe-cies continues to attract research interest. In Brazil,Dos Santos andValenti (2002) have shown that stock-ing densities of up to 6m�2 M. rosenbergii PL did nota¡ect the production of tilapia (Oreochromis niloticus)stocked at1m�2 over a175-day experimental period,and required neither additional feeding nor signi¢-cant changes in management. At the highest prawnstocking rate, 3721kgha�1of tilapia (¢nal averageweight 519.6 g) and 818 kg ha�1of prawns (¢nal aver-ageweight14.7 g) were obtained. Lower prawn stock-ing rates achieved larger ¢nal average prawnweights(34 g at 2m�2 and 23 g at 4m�2). Achieving addi-tional yield without additional feed improves the sus-tainabilityof the system. In Puerto Rico Garc|¤ a-Pe¤ rez,Alston and Corte¤ s-Maldonado (2000) had stockedone 7^8 g tilapiam�2, with or without juvenileprawns (1.0^1.3 g) at 7m�2, and compared withprawns alone at 7m�2, in an experiment lastingabout145 days.The feeding rate was adjusted accord-ing to the mean biomass. This work showed that thisform of polyculture has the potential of maintainingthe yield of tilapia productionat non-signi¢cantly dif-ferent levels (2942 kg ha�1, in monoculture and2769 kgha�1 in polyculture) with similar average ¢-nal weights. However, while 1367 kg ha�1 of prawnswas obtained in monoculture, this fell to 951kg ha�1

in polyculture. Furthermore, the meanweights of theprawns were signi¢cantly di¡erent (55 g in monocul-ture and 31g in polyculture). It would have been in-teresting to compare the results of these two papersfurther if Dos Santos andValenti (2002) had includeda treatment where prawns were stocked alone.The work of Tidwell, Coyle,Van Arnum,Weibel and

Harkins (2000b) suggests that rearing tilapia (O. nilo-ticus) with M. rosenbergii may improve overall ponde⁄ciency. In this experiment, tilapias were grown incages attached to a £oating deck at the deep end ofthe pond.Kurup and Ranjeet (2002) surveyed 122 farms in

1998^2001in Kuttanad, India (the‘rice bowl’of Kera-la); 75 used polders for M. rosenbergii culture, al-ternating with rice. Twenty farms practised

monoculture and 55 grew prawns in polyculturewith Indian major carps such as catla (Catla catla)and rohu (Labeo rohita), and grass carp (Ctenopharyn-godon idella). Comparing monoculture with polycul-ture, these authors reported yields of 95^1297 kgha�1of prawns in monoculture, compared with 70^493 kgha�1of prawns and 200^1200 kg ha�1of ¢shin polyculture. Revenue generation indicated thatmonoculture was generally more advisable thanpolyculture in this situation. The ¢nal conclusionwas that freshwater prawn culture was a useful wayof increasing income and employment where doublecropping of rice was not possible because of monsoon£ooding. Kurup, Ranjeet and Hari (2002) providefurther information con¢rming this matter, describ-ing it as an‘eco-friendly’ form of aquaculture.

Transport survival

The important topic of the survival of prawns duringtransport from one location to another has alsoattracted research attention. Juvenile prawns areusually transported in plastic bags ¢lled with waterand air or oxygen, often inside styrofoam coolers.Frequently, losses are experienced because of dete-riorating water quality and stress. Coyle,Tidwell,VanArnumandWeibel (2000) reported the e¡ects of den-sity on survival and associated water quality para-meters, transporting animals at 10, 25 and 50 g L�1

(since they were using 0.26-g animals, this wasequivalent to approximately 38, 96 and 192 in-dividuals L�1). Their ¢ndings were that although to-tal and unionized ammonia concentrations (and to alesser extent nitrite levels) increased with density,they were not considered to reach lethal levels at thetemperature (22 1C) and pH (average 8.1) conditionsused, up to the highest stocking transport density(50 g L�1). The signi¢cantly lower survival levelswhen prawns were transported at 50 and 25 g L�1,compared with 10 g L�1 were attributed to reduceddissolved oxygen levels at higher transport densities.After 8 h, DO2 was 3.2 ppm at 10 g L�1, but only1.6 ppm at 25 g L�1 and 1.3 ppm at 50 g L�1.Although juveniles can tolerate DO2 levels as low as1.0 ppm for short periods, the levels found in thisstudywere likely to cause stress. Recommending thatjuveniles should not be transported at densities in ex-cess of 10 g L�1 (e.g. about 38 individuals weighing0.26 g) in sealed containers when the transport timewas eight ormorehours, these researchers noted thathigher transport temperatures would certainly in-crease oxygen consumption and nitrogen excretion,



making further reductions in transport density es-sential. In terms of numbers these transport densityrecommendations seem much lower than those re-ported or suggested by other authors for youngPL. For example, densities in closed containers of250^417 L�1 for short transport times in Brazil and666 L�1 for 24^36 h in Thailand were cited by Cor-reia, Suwannatous and New (2000); 100 L�1 whenplastic straw was included as a transport habitat byVadhyar, Nair, Singh and Joshi (1992); 125^250 L�1

for up to 16 h by Valenti and New (2000); and 250^400 L�1 for up to 16 h by New (2002a). However,since young PL only weigh approximately 0.01geach, these densities all fall well within the maxi-mum transport density by weight recommended byCoyle and colleagues (2000). Thus 10 g L�1 could berecommended as a general maximum transport den-sity for PL and juveniles but, for practical purposes, itwould be more useful to know the numbers, ratherthan theweight, per unit volume. Larger animals (in-cluding broodstock) are also sometimes transportedlong distances.This topic therefore needs further elu-cidation, so that practical tables could be derived,which would state the number of animals recom-mended for di¡erent animal weights, under variouslevels of temperature and pH, and for varying trans-port times.

A glance into the future of freshwaterprawn farming

Forecasting the future is little more than gazing intoa telescope and expecting. However, it is di⁄cult toresist the temptation.

Characteristics of the sector

In looking at global trends over the period from nowuntil 2006, I would expect that:� Chinese production ofM. nipponensewill continueto increase, for its domestic market and (hopefully)China will commence declaring its production ofthis species in its statistical returns to FAO;

� Chinese production of M. rosenbergii will expandand this species will become an export product;

� China may develop commercial farming ofM. mal-colmsonii and (perhaps) of M. amazonicum, whichis larger than M. nipponense, but is still morelikely to appeal to the domestic market thanM. rosenbergii;

� production in India and Bangladeshwill markedlyincrease, mainly ofM. rosenbergii, for both domes-tic and global markets;

� the output of Thailandwill expand signi¢cantly, asthe country realizes that a global market is becom-ing available and that the culture of freshwaterprawns may be more environmentally acceptablethan marine shrimp;

� Brazil will become a signi¢cant producer of bothM. rosenbergii andM. amazonicum;

� other Latin American and African countries willincrease their activity in this ¢eld;

� Research on the culture of freshwater prawns intemperate zones, pioneered in the USA, will be-come utilized in the temperate zones of othercountries;

� markets for freshwater prawns will continue toexpand in both industrialized and developingcountries.

Future scale of production

In considering the e¡ects of these expectations onthe global output of farmed freshwater prawns, I haveinitially ignored the largest producer, China, partlybecause such a large proportion of its total produc-tion in the last 3 years (namely that contributed bythe indigenous speciesM. nipponense) is only an esti-mate. This, in addition to the very rapid expansion infarmedM. rosenbergii production reported to FAO be-tween 1996, when it suddenly reported an output ofover 37000mt, and 2001, when an output of over128000mt was reported, totally skews any globalpicture. It is extremely di⁄cult to make meaningfulglobal forecasts if China is included. However, I willtry!Let us look at the possible future in the world ex-

cluding China ¢rst. As noted earlier in this review,the average expansion rates for M. rosenbergii in theworld outside China were between about 12% and30% yr�1, depending on whether we consider thewhole decade from 1992 to 2001, or consider onlythe period 1999^2001. It would probably be over-op-timistic to imagine that freshwater prawn farmingwould continue to expand at 30% year�1 in the fu-ture! However, even if the more modest expansionrate experienced between 1992 and 2001 continuesfor the rest of the current decade, global production(excluding China) will be signi¢cantly greater by2010. Figure10 shows that continued average expan-sion rates at 12% year�1 would result in a global



farmed output of M. rosenbergii alone of over159000mt by 2010. The estimate shown in Fig. 10not only excludes the potential production from Chi-na but also the production of other Macrobrachiumspp. and the production of Viet Nam, which is cur-rently ‘lost’within the FAO category ‘freshwater crus-taceans nei’.So now let us look at what may happen if we in-

clude potential growth of the sector in China andVietNam. It is entirely possible that the output of M. ro-senbergii and M. nipponense in China in 2010 will bedouble that in 2001 (whichwould result in a produc-tion approaching 500000mt) and that the assumedproduction of M. rosenbergii in Viet Nam and otherminor producing countries not speci¢cally reporting

their output asM. rosenbergii (the nei categories) mayalso double between 2001and 2010. If this happens,and production in the rest of the world expands at12% year�1 (the same as in the decade 1992^2001),the total output of freshwater prawns by the end ofthis decade would exceed 700000mt year�1 (Fig.11).Figure 12 shows what would happen if Chineseand Vietnamese production trebled and the ex-pansion rate in the rest of the world continuedat 30% year^1, the rate achieved between 1999and 2001. If that happened the global production offreshwater prawns would reach over 1.4million -mt year�1by 2010.This then is the potential picture. Based on a dou-

bling or trebling of output in China and Viet Nam

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

BASED ON 1992-2001GROWTH RATE(12%/yr)

BASED ON 1999-2001GROWTH RATE (APR30% /yr)

Figure 10 Estimates (mt) of futureproduction of farmed Macrobra-chium rosenbergii (excluding Chineseand ‘nei’ production) in the currentdecade.

M. rosenbergii (excluding China)

Other species and Chineseproduction addedTOTAL

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

800,000

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Figure 11 Estimate (mt) of the fu-ture production trend based on adoubling of Chinese and‘nei’produc-tion between 2001 and 2010 anda 12% annual expansion rate forMacrobrachium rosenbergii in the restof the world.



and continuing expansion rates of between12% and30% year�1 in the rest of the world, the farmed pro-duction of Macrobrachium spp. would be between700000 and1.4millionmt by 2010. In these scenar-ios, the potential production of other Macrobrachiumspp., such as M. malcolmsonii, M. vollenhovenii andM. amazonicum have not been considered.Being cautious myself, I would expect that total

global freshwater prawn productionwill be in the re-gion of 750000^1000000mt year�1 by the end ofthe current decade. This would place its productionalmost in the same order of magnitude as the marineshrimp farming sector now but, of course, entirelydi¡erent in its characteristics.

Research needs

Finally, I would just like to present a‘bullet’ list of themajor topics where I believe further research anddevelopment would signi¢cantly support the futuredevelopment of commercially successful and envir-onmentally and socio-economically sustainablesmall- and large-scale freshwater prawn farming.In my view, the important topics are:

� Careful considerationof the economic implicationsof every experiment. Cost considerations should beincorporated into experimental design, so thatresults can be quanti¢ed in ¢nancial, as well aspurely scienti¢c terms. In this way, the really im-portant research ¢ndings can more quickly beadopted in farming practice and bene¢t both farm-ers and consumers.

� Freshwater prawns remain undomesticated,although unconscious (and sometimes negative)selection may have taken place in countries wherethe parent stocks were introduced in very smallnumbers. Conventional selection and breeding for

desirable traits or (if consumers will accept it) bygene manipulation and transfer is essential to im-prove the viability of freshwater prawn farming.Further work on hybridization to combine the at-tractive traits of various species is also warranted.For example, it may be possible to combine the de-licate £avour of one species, which commands apremium price, with the more rapid growth rateand/or ¢nal market size of another.

� Genotype/phenotype e¡ects on HIG need muchmore elucidation. Knowledge on this topic is prob-ably a prerequisite for successful selection, im-proved management, and enhanced pro¢tability.

� I have often remarked that there should be less re-search on the hatchery phase of species of ¢sh andcrustacea, where so much is already known andsuccessful hatchery technologies exist and havebeen so widely put into practice. In my view, re-search on the nursery and grow-out phases,although such experiments are less easily repli-cated and need to be lengthier than work withlarval stages, should be a major priority. In thisaspect of research work, I include all aspects ofmanagement, including feeding, health manage-ment, nutrition, water management, optimizingand maintaining biomass levels to improve pro-duct marketability (in other words adaptingmanagement procedures to increase the propor-tion of marketable prawns; of course, the de¢nitionof what is marketable depends on the speci¢ccharacteristics of the market that the farmerswish to supply) and, perhaps most important ofall for this genus, practical and e¡ective sizemanagement.

� Despite my apparent bias against work with thelarval stages, new information that should im-prove hatchery viability (such as those mentionedearlier in this review) is still being generated.

M. rosenbergii (excludingChina)

Other species andChinese productionadded

TOTAL

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,000

1,600,000

2001 2002 2003 2004 2005 2006 2007 2008 2009 02010

Figure 12 Estimate (mt) of the futureproduction trend based on a treblingof Chinese and ‘nei’ productionbetween 2001 and 2010 and a 30%annual expansion rate for Macrobra-chium rosenbergii in the rest of theworld.



Further work on factors a¡ecting the broodstockand larval phases of freshwater prawn farming,particularly on sustainable health management inhatcheries and the e¡ect of broodstock nutritionand management on larval quality merits contin-ued attention. In particular, resolution of theapparently con£icting results of studies on thesubsequent performance of early versus late-hatching prawns in grow-out seems important.However, I repeat my opinion that expenditure onthese topics should not be at the expense of ne-glectingworkon the nurseryand grow-out phases.The ideal solution would be experiments that fol-low the comparative performance of di¡erent po-pulations through both hatchery and grow-outphases. Adequate research funding and long-termcommitment of both research managers and re-search scientists are prerequisites for this type ofexperimental work.

� It is clear that, in many locations, there may be va-lue in the polyculture of freshwater prawns withother crustacea and/or ¢n¢sh; further research toquantify bene¢ts is required.Work on the integra-tion of freshwater prawn farming with other formsof activity sharing the same resources, such ascrop and livestock production, would also bevaluable.

� Socio-economic and environmental research isalso essential, to ensure that freshwater prawnfarming is responsible and sustainable, and thatconsumer attitudes towards our products (bothin international and domestic markets) remainpositive.

� The use of suitable harvesting, handling and pro-cessing techniques are also important to ensurethat our products are of high quality. In this area,I think that further studies on the e¡ect of variousmethods of handling prawns on product qualityare vitally important. The critical period betweenremoving prawns from the rearing enclosure andcommencing their transfer to the sites where freshor chilled products are marketed, or to processingplants, merits particular attention.

� Finally, I would like to stress again that considera-tion of cost factors need to be a facet of all ex-perimental protocols. Research results may bebiologically interesting but economically impossi-ble to apply. Please think carefully about this whendesigning and reporting your experimental work.Those of us who are involved in peer reviewfor aquaculture journals should also bear thisin mind.

Acknowledgments

I would like to sincerely thank Dr C. Mohanakumar-an Nair, the Convenor of the International Sympo-sium on Freshwater Prawns, for inviting me topresent the keynote address (whichwas based on thisreview paper) at the College of Fisheries, Kerala Agri-cultural University, Kochi, India in August 2003.Much gratitude is also due to the Vice-Chancellor ofthe University, Dr K. V. Peter, and to the Dean of itsCollege of Fisheries, Dr D. D. Nambudiri, for hostingthe symposium. I would also like to thank the count-less people who have helped me over several decadesto gather material on the topic of freshwater prawnculture and research for inclusion in my own publi-cations, where appropriate acknowledgments will befound.

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