Aquaculture 307 (2010) 206–211

Contents lists available at ScienceDirect

Aquaculture

j ourna l homepage: www.e lsev ie r.com/ locate /aqua-on l ine

Population structure of pond-raised Macrobrachium amazonicum with differentstocking and harvesting strategies

Bruno L. Preto, Janaina M. Kimpara, Patricia Moraes-Valenti, Wagner C. Valenti ⁎Sao Paulo State University, Aquaculture Center (Caunesp), Via de Acesso Prof. Paulo Donato Castellane, s/n 14884-900 Jaboticabal, SP, Brazil

⁎ Corresponding author. Tel.: +55 16 32092620; faxE-mail address: wcvalenti@gmail.com (W.C. Valenti

0044-8486/$ – see front matter © 2010 Elsevier B.V. Adoi:10.1016/j.aquaculture.2010.07.023

a b s t r a c t

a r t i c l e i n f o

Article history:Received 15 January 2010Received in revised form 18 July 2010Accepted 21 July 2010

Keywords:MacrobrachiumMorphotypesSex ratioGrading juvenilesSelective harvesting

The effect of size-grading of juveniles prior to stocking, as well as selective harvesting, on the populationstructure of pond-raised Macrobrachium amazonicum was studied. A randomized-complete-blocks designwith 4 treatments and 3 replicates was used. The treatments were: upper size-graded juveniles, lower size-graded juveniles, ungraded juveniles (traditional), and ungraded juveniles with selective harvesting. Twelve0.01 ha earthen ponds were stocked at 40 juveniles m−², according to the relevant treatment. Every threeweeks, random samples from each pond were obtained for biometry, and after 3.5 months, the ponds weredrained and completely harvested. Animals were then counted, weighed, and sexed; males were sorted asTranslucent Claw (TC), Cinnamon Claw (CC), Green Claw 1 (GC1), and Green Claw 2 (GC2), and females asVirgin (VF), Berried (BE), and Open (OF). The prawns developed rapidly in the ponds, attaining maturity anddifferentiating into male morphotypes after about 2 months in all treatments. The fast-growing juveniles(upper grading fraction)mostly did not constitute the dominant males (GC1 and GC2) in the adult population.Population development was slower in ponds stocked with Lower prawns, whereas selective harvestingincreased the frequency of GC1 and reduced the final mean weight of GC2 males. The proportion of malesincreased throughout the culture period, but was generally not affected by the stocking or harvestingstrategies. Grading juveniles and selective harvesting slightly altered the population dynamics and structure,although the general population development showed similar patterns in ponds stocked with upper, lower,and ungraded juveniles, or selectively harvested.

+55 32032268.).

ll rights reserved.

© 2010 Elsevier B.V. All rights reserved.

1. Introduction

The Amazon River prawn Macrobrachium amazonicum occurs inalmost all of South America, from Venezuela to northern Argentina(Holthuis, 1966; Pettovello, 1996). This species is highly important forartisanal fisheries in Amazonia and the Brazilian Northeast (Maciel andValenti, 2009), and has a huge potential for aquaculture (Kutty, 2005;New, 2005). It may reach 16 cm and 30 g (Moraes-Valenti and Valenti,2010), but a population contains different male morphotypes, whichcauses wide variability in the animals' size (Moraes-Riodades andValenti, 2004). Heterogeneous growth is amajor problem in freshwater-prawn farming, because the slower growth of part of the populationresults in a high percentage of small animals with low market value(Daniels et al., 1995).

Grading juveniles before stocking grow-out ponds or seining theponds after prawn maturation are techniques to reduce the negativeeffects of this heterogeneous growth (New, 2002; Valenti et al., 2010).Grading divides the population in larger (“uppers”) and smaller(“lowers”) animals. Studies on Macrobrachium rosenbergii have shown

that after the grow-out period, the “upper” subpopulation has a more-developed population structure compared to the “lower” subpopulation(Karplus et al., 1986, 1987; Tidwell et al., 2003, 2004a). The directrelationship between the percentage of smallmales and higher stockingdensity that is normally found in ungraded populations, did not occurwhen juveniles were graded (Daniels et al., 1995). Selective harvestingthroughout the rearing cycle consists of harvesting dominantmales andmature females by seining the pond (New, 2002; Valenti et al., 2010).The prawns removed are large-sized, but have a slower growth rate andinhibit the growth of smaller individuals. Therefore, selectively harvest-ing and grading juveniles before stocking may alter the populationstructure in the ponds. However, the effectiveness of this procedure hasnot yet been confirmed for M. amazonicum.

The strategies to farm freshwater prawns in the WesternHemisphere were reviewed by Valenti and Tidwell (2006). Stockingjuveniles in grow-out earthen ponds for 3–4 months is especiallypromising, because it optimizes land use and maximizes productivity.This strategy allows one profitable rearing cycle in temperate regions,two in subtropical, and three in tropical regions. Although somestudies have demonstrated the feasibility of this strategy for M.rosenbergii (Tidwell et al., 2003, 2004a,b, 2005), no information isavailable for the Amazon River prawn.

207B.L. Preto et al. / Aquaculture 307 (2010) 206–211

The aim of this study was to evaluate the influence of gradingjuveniles before stocking, as well as selective harvesting, on thepopulation structure ofM. amazonicum raised in ponds for 3.5 months.Although some previous reports have described the effect of gradingjuveniles on the population development of the Asian species M.rosenbergii, none has assessed the effect of selective harvesting on thepopulation characteristics of any Macrobrachium species.

2. Material and methods

This study was conducted in the Crustacean Sector, AquacultureCenter, Jaboticabal, state of São Paulo, Brazil. Newly metamorphosedM. amazonicum post-larvae (PL) were stocked for 15 days in indoornursery tanks (7 PL/L), and then for 30 days in outdoor nursery ponds(200 PL/m²). Then, part of these animals were graded in a grader box(Bernauer model D6001) with a 5 mm mesh, resulting in twosubpopulations: “uppers” (1/3 of the total), which were retained inthe grader box, and “lowers” (2/3 of the total), which passed throughthe bars.

Twelve 0.01-ha earthen ponds (1 m deep) were drained, allowedto dry, and limed (1 t/ha CaCO3). Then, they were filled with reservoirwater after it passed through a mechanical filtration system, andstocked at 40 juveniles/m². The water exchange rate was maintainedat ~30% per day. A randomized-complete-blocks design with fourtreatments and three replicates was used. The Upper treatmentconsisted of stocking ponds with the subpopulation of larger animals(0.59±0.02 g). In the Lower treatment, ponds were stocked withsmaller juveniles (0.39±0.03 g). The Traditional treatment consistedof stocking ponds with ungraded juveniles (0.51±0.03 g). In theSelective-harvesting treatment, ponds were stocked with ungradedjuveniles (0.50±0.04 g), and two intermediate harvests were carriedout 10 and 13 weeks after stocking, using a 12-mm mesh net. Pondsseining started after dominant males appeared in the population.Each pond was seined 3 times; dominant males and mature femaleswere removed, while all stunted males and immature females werereturned to the relevant pond.

At the beginning of the rearing cycle, the prawns were fed acommercial pelletized diet formulated for penaeid shrimps (35% crudeprotein) at the rate of 9% of their biomass. The feeding rate was reducedby 2% per month, so in the 13th week the prawns were receiving 3% oftheir biomass. Prawn biomasswas estimated in each pond based on theindividual mean weight obtained by sampling (every 3 weeks) and theexpected survival and growth, assuming 1% mortality and 20% weightgain per week. Two equal portions of diet were supplied at 08:00 and16:00 h. When the dissolved oxygen in the morning was between 2.5and 3.5 mg/L, this quantity was reduced by half; and when values werebelow 2.5 mg/L, feeding was canceled. On those (rare) occasions,aerators (Bernauer model B-500 AQUAHOBBY) were turned on forabout 5 h.

The main physical and chemical water characteristics weremonitored (Table 1). Water inflow was determined at the inlet pipe of

Table 1Means (±standard deviation) of water variables measured during the rearing cycle.

Variables Treatmentsa

Upper

Water exchange rate (% by day) 27.3±12.2Temperature morning (°C) 27.1±0.9Temperature afternoon (°C) 28.7±1.5Transparency (cm) 46±11pH 7.83±0.45Dissolved oxygen morning (mg L−1) 4.22±1.32Dissolved oxygen afternoon (mg L−1) 8.14±3.06N-Total ammonia (μg L−1) 77.7±49.3

aNo significant difference was found among treatments.

each pond, using a graduated bucket; from this, the daily waterexchange ratewas calculated.Water temperature and dissolved oxygenwere monitored daily at 07:00 and 17:00 h, using a YSI model 55temperature/oxygen meter. Water transparency, pH, N-total ammonia,and water inflowwere measured weekly (15:00 to 17:00 h). Transpar-ency and pH were measured using a Secchi disk and a YSI model 63 pHmeter, respectively. N-total ammonia concentration was determinedaccording to Solorzano (1969), using a Hach DR 2000 spectrophotom-eter. These parameters showed similar values to that obtained inprevious experiments on M. amazonicum grow-out in ponds (Moraes-Riodades et al., 2006; Keppeler and Valenti, 2006). They werepresumably suitable for culture, based on the information available forM. rosenbergii farming (New, 2002; Boyd and Zimmermann, 2010). Inaddition, no diseases were observed and survival was high (~70%),suggesting that the conditions were suitable for prawn development.When transparency exceeded 50 cm (8th week), simple superphos-phate andureawere added to theponds in theproportionof 8 kgP2O5/haand 2 kg N/ha (Boyd and Zimmermann, 2010).

Every three weeks, 30 prawns from each pond were sampled andanalyzed.Animalswereweighed (MarteA500, 0.01 g) and sexed.Maleswere sorted as “Translucent Claw” (TC), “Cinnamon Claw” (CC), “GreenClaw 1” (GC1), and “Green Claw 2” (GC2), according to Moraes-Riodades and Valenti (2004). Females were classified as virgin (VF),berried (BF), and opened (adult non-ovigerous, OF), according to thecriteria of Bauer (2004) for Caridea. After the analyses, the prawnswerereturned to the ponds. The frequency of male morphotypes and femalegroups and the sex ratio were determined for each treatment over time.The sex ratio was obtained by dividing the number of males by thenumberof females. Althoughexternal sexual differentiation appeared atthe 3rd week, data from the first biometrywere not included in the sex-ratio analyses, because the presence of undifferentiated individuals andthe large number of virgin females, which are difficult to separate fromimmature prawns, couldmask the proportions. Except for sampling, thesame procedure was used in the selective harvests. In the first one, allanimals were analyzed, whereas in the second one, a random sample(N≥50) from each pond was analyzed.

After 3.5 months, the ponds were drained and all the prawns wereharvested. Ten percent of the animals in each pond were randomlysampled and analyzed as previously described. Then, the mean valueof frequencies and weights of male morphotypes and female groupswere determined. The animals removed by selective harvesting weresummed to the animals captured at total harvest for all analyses. Theweights of harvested animals were grouped in classes of 1 g, and thefrequency distribution was determined for each treatment.

Data normality and homocedasticitywere tested usingKomolgorov–Smirnov and Brown–Forsythe tests, respectively. Because these condi-tions were satisfied, data were subjected to two-way ANOVA, F-test,performed as amixedmodel, inwhich treatments is the fixed factor andblock is the random factor; the null hypothesis of equal means onall treatments was tested. When differences were significant, meanvalues were compared by Tukey or Fisher LSD tests, depending on the

Lower Traditional Selective harvesting

31.0±17.5 28.0±15.4 29.5±15.627.3±0.7 27.1±1.0 27.1±0.929.1±1.0 28.8±1.5 28.8±1.950±7 49±8 55±11

7.97±0.40 7.88±0.35 7.85±0.424.35±0.64 4.43±0.97 4.35±1.299.94±1.96 8.24±2.28 7.75±2.5356.5±39.9 92.2±38.0 115.5±84.4

208 B.L. Preto et al. / Aquaculture 307 (2010) 206–211

coefficient of variation. Percentages were previously arcsin√x trans-formed, but the original values are presented. The sex ratio wascompared using the G-test (Sokal and Rolf, 1995). Statistical analyseswere performed in SAS software v.9 (version 9.0; SAS Institute Inc.). Inall cases, it was considered that samples differed significantly at 5%probability.

3. Results

External sexual differentiation was observed at the 3rd week,when prawns attained 0.96–1.22 g and 80–90% of prawnswere sortedin TC or VF in all treatments (Fig. 1). The frequency of TCwas 40 to 47%of the entire population, and then decreased over time, stabilizing atabout 10% from the 12thweek on. The frequency of CCwas very low inthe 3rd week (1.1–4.4%), but then dramatically increased to the 12thweek, and afterwards stabilized at ~40% of the population. The GC1morphotype appeared in the 6th week, and its frequency increasedslightly throughout the period of culture. The GC2 males appeared inthe 9th week, except for the Lower treatment, in which they appearedin the 12th week. The frequency of VF decreased throughout theculture to ~10% in the Lower treatment, and almost to zero in theothers at the 15th week (Fig. 2). Females began to mature in the 6th

Fig. 1. Frequency of male morphotypes throughout the rearing cycle under differentmanagement techniques. TC = translucent claw, CC = cinnamon claw, GC1 = greenclaw 1, GC2 = green claw 2.

Fig. 2. Frequency of female groups throughout the rearing cycle under differentmanagement techniques. VF = virgin females, BF = berried females, OF = openedfemales.

week, and the frequency of BF increased rapidly from the 6th to 9thweeks, reaching ~25% at the 15th week (Fig. 2). The percentage of OFremained low during the culture period, reaching ~7% at the 15thweek (Fig. 2).

The population structure at harvest (including the animalsremoved in the two selective harvests) was similar among thetreatments (Table 2). Significant differences were found for TC, GC1,andVF. The Selective-harvesting treatment had the highest proportionof GC1 prawns, and the Traditional and Lower treatments had thelowest ones; the frequency of GC1 prawns in the Upper treatment didnot differ from the Lower, Traditional, and Selective-harvestingtreatments. The Upper and Traditional treatments showed a lowerproportion of TC than the Lower treatment, which in turn had thehighest percentage of VF.

Table 2Mean percentages (±standard deviation) of male morphotypes and female groups inrelation to the total quantity of harvested prawns. TC= translucent claw, CC= cinnamonclaw, GC1=green claw1, GC2=green claw2, VF=virgin females, BF=berried females,OF = opened females.

Groups Treatments1

Upper Lower Traditional Selective harvesting

TC 9.3±5.7b 17.3±3.1a 10.5±4.1b 12.5±4.1ab

CC 37.1±5.1a 33.8±4.7a 39.6±3.7a 34.8±3.0a

GC1 8.0±0.5ab 5.6±1.2b 6.6±1.8b 9.6±1.1a

GC2 8.2±2.3a 5.7±2.6a 9.2±1.1a 5.7±0.4a

VF 3.0±0.7b 8.5±1.5a 2.2±0.2b 2.4±2.5b

BF 27.2±6.3a 22.8±5.6a 24.9±6.3a 28.3±5.1a

OF 7.2±2.1a 6.3±3.9a 7.0±3.0a 6.7±1.9a

1Mean values followed by the same letter in the same row do not differ significantly(pN0.05).

Table 3Means (±standard deviation) of the sex ratio (# of males / # of females) for eachtreatment throughout the culture period.

Weeks Treatments1

Upper Lower Traditional Selective harvesting

6 0.8±0.2Aa 0.6±0.2Aa 1.1±0.7Aa 0.6±0.2Aa

9 1.1±1.0Ab 2.0±0.6Ba 1.2±0.4Ab 0.7±0.5Ab

12 2.1±0.8Ba 1.6±0.1Ba 1.6±0.6ABa 2.2±0.8Ba

15 1.8±0.6Ba 1.6±0.6Ba 2.0±0.7Ba 1.9±0.4Ba

1Mean values followed by the same capital letter in the same column or by the samesmall letter in the same row do not differ significantly (pN0.05).

Fig. 3. Frequency of prawns removed in each type of harvest in the Selective-harvestingtreatment, by weight classes (g).

209B.L. Preto et al. / Aquaculture 307 (2010) 206–211

The sex ratio differed among weeks, increasing throughout theculture period (Table 3). There was a higher proportion of females inthe 6th week, except in the Traditional treatment. The proportion wasinverted during the cycle, and males predominated from the 12thweek on. A significant difference was found among treatments only atthe 9th week.

The mean weight of harvested GC2 and BF differed significantlyamong the treatments (Table 4). GC2 males reached the lowest valuein the Selective-harvesting treatment. The highest BF mean weightwas found in the Selective-harvesting treatment, and the lowest wasfound in the Lower treatment. Selective harvesting removed only22.0±0.0% of the total harvested prawns. The removed group wascomprised of 36.9±3.8% BF, 30.2±6.9% GC1, 21.7±3.8% GC2 and8.7±4.1% OF;. GC1 and GC2 males generally weighed more than 6 g,whereas BF and OF weighed 3–5 g. The mean weight of removedprawns was 5.7±0.4 g. The process was efficient in selecting thelarger individuals, whereas the smaller ones remained in the pondsup to the total harvest (Fig. 3).

All the populations showed positive asymmetrical distributions ofprawns in size classes at the 15th week (Fig. 4). The group of smalleranimals wasmore numerous, and was formed by females, TC, CC, and afew GC1 males. The group of larger animals was composed by GC1 andGC2 males. The most frequent weight class was 4 g in the Selective-harvesting treatment, and 3 g in the others (Fig. 4). Prawns reached12 g in the Selective-harvesting treatment, and 15–16 g in the others.Total harvested biomass ranged from1026±184 to1140±292 kg ha−1

and did not differ among the treatments.

4. Discussion

Macrobrachium amazonicum developed rapidly in the ponds,attaining maturity and differentiating into male morphotypes about2 months after stocking.M. amazonicum reproduces many times duringits lifespan, and females may mature sequentially, when the environ-mental conditions are appropriate (Maciel and Valenti, 2009). There is atrade-off between energy andmaterials allocated to reproductive effortand growth (Begon et al., 2006). Therefore, the early maturationobserved in the present experiment indicates that the prawns

Table 4Mean weights (±standard deviation) (g) of male morphotypes and female groupsharvested. TC = translucent claw, CC = cinnamon claw, GC1 = green claw 1, GC2 =green claw 2, VF = virgin females, BF = berried females, OF = opened females.

Groups Treatments1

Upper Lower Traditional Selective harvesting

TC 1.6±0.1a 1.5±0.0a 1.6±0.2a 1.5±0.0a

CC 2.7±0.0a 2.6±0.1a 2.5±0.2a 2.6±0.0a

GC1 6.8±0.3a 6.3±0.1a 6.4±0.4a 6.0±0.2a

GC2 10.8±0.3a 10.1±0.0a 10.2±0.4a 8.4±0.3b

VF 2.9±0.2a 2.8±0.2a 2.8±0.6a 2.7±0.9a

BF 4.0±0.2ab 3.6±0.4b 3.8±0.2ab 4.0±0.2a

OF 3.6±0.3a 3.3±0.3a 3.5±0.1a 3.6±0.3a

1Mean values followed by the same letter in the same row do not differ significantly(pN0.05). Fig. 4. Frequency of harvested prawns, by weight classes, in each treatment.

210 B.L. Preto et al. / Aquaculture 307 (2010) 206–211

prematurely devoted energy to the reproductive process, decreasingtheir growth. Grading juveniles before stocking and the use of selectiveharvesting slightly altered the population dynamics and structure,although the general population development showed similar patternsin ponds stocked with upper, lower, and ungraded juveniles, orsubjected to selective harvesting. This suggests that M. amazonicumpopulation events may be an intrinsic characteristic of the species,although modulated by environmental factors.

At the 3rd week, (~2 months after metamorphosis), males werecomposed mainly of the TC morphotype. The proportion of this groupdecreased throughout the rearing cycle, while CC increased. GC1 andGC2 males appeared at the 6th and 9th weeks, respectively, and thentheir proportion increased to the 12th week (~4 months aftermetamorphosis) and stabilized. This result indicates that TC is the firstmature male stage and originates the other morphotypes, followingthe sequence TC–CC–GC1–GC2. Moraes-Riodades and Valenti (2004),based only on morphological data (non-temporal samples), suggestedthe same sequence for the development ofM. amazonicummales,whichis reinforced by the present results. A similar pattern occurs in M.rosenbergii, in which the Small Male (SM) morphotype originatesOrange Claw (OC) and Blue Claw (BC) males, sequentially (Daniels,1993). The low frequency of GC2 males observed in the present studymight result from the short period of culture. However, the percentageof GC2 in populations raised in ponds for 5.5 months at the samestocking density (40 ind/m2) used in the present study was ~11%(Moraes-Valenti et al., 2010). Therefore, this small proportion may be apopulation characteristic of M. amazonicum.

The status of M. amazonicum juvenile males in the populationprobably plays a minor role in their subsequent morphologicaldevelopment. The fast-growing juveniles will mostly not constitutethe dominant males in the adult population. There was no increase inthe number of large males in the Upper treatment, which showed a sexratio and male and female population structure very similar to theungraded population. This result differs from previous findings for M.rosenbergii, in which jumper juveniles will transform into large males(OC and BC) and laggards will generally transform into SM (Karplus,2005). The development of a M. amazonicum population may be apredetermined directional process, which leads to a stable structuremodulated by environmental factors. Some natural populations do notshow a male morphotype structure (Maciel and Valenti, 2009),reinforcing the hypothesis that population development depends onenvironmental factors.

The population structure developed more slowly in the Lowertreatment. GC2 males appeared 3 weeks after they appeared in theother treatments, and there were significantly higher frequencies of TCmales and VF females 3.5 months after stocking. Karplus et al. (1986,1987) also observed that the lower fraction of M. rosenbergii juvenilescontained more stunted males and virgin females than the upper-graded and ungraded prawns. In addition, these juveniles mainlyoriginate the small SM morphotype (Karplus, 2005). Probably, lowerjuveniles of bothM. amazonicum andM. rosenbergii, although they retainthe full development capacity, are less able to exploit the environmentand use the available resources, and therefore they develop slowly.

Selective harvesting reduced the frequency of larger prawns in theoutput biomass, instead of increasing it. Although larger animals in theponds were removed by seining at 2.5 and 3.0 months after stocking,this resulted in both absence of prawns above 12 g and a significantreduction in the final size of GC2 (8.4 g in Selective harvesting, whereasit was N10 g in the other treatments). This indicates that GC2 is not aterminal growth phase, but that these males continue to grow. TheSelective-harvesting treatment had the highest frequency of GC1males.The removal of large males (GC1 and GC2) may have allowed the rapidtransformation of CC into GC1. However, the short time between theselective and total harvests (15–30 days)mighthavenegatively affectedthe transition fromGC1 toGC2. Themodal class of prawnsproducedwas4 g in theSelective-harvesting treatment,whereas itwas3 g in the other

treatments. This suggests a change in thepopulationdynamics. Probablythere was not enough time for significant growth and development ofthe stunted TC and CC males. Hence, selective harvesting may not be asuitable management strategy for short-term culture.

Theproportionofmales increased throughout the cultureperiod, butin general was not affected by the stocking or harvesting strategies. Inthe 6th week, there was a higher proportion of females in all except theTraditional treatment. The proportion was inverted during the cycle,and it varied from 1.6 to 2.0 in the 15thweek. In the 6th and 9th weeks,there were many virgin females, some of which may in fact have beenundifferentiated males, which would be correctly identified in thefollowingweeks. In addition, differentialmortality of females and/or sexreversal may have occurred. No information on differential mortality incarideans was found in the literature. Sex reversal is frequent incarideans, although protogyny is very uncommon (Bauer, 2004).Moraes-Valenti et al. (2010) hypothesized that the increase in theproportion of males in M. amazonicum may be a mechanism to avoidintraspecific competition when resources become scarce, as occurswhen prawns grow. In this situation, it would be very advantageous tomaintain part of the population as stuntedmales, which consume fewerresources. The asymmetrical distribution of prawn sizes observed in thepresent study results from the high frequency of the small TC and CCmales compared to the large GC1 and GC2 males. This structure mayenable the population as a whole to economize on resources.

Grading juveniles before stocking and selective-harvestingmanage-ment strategies did not contribute to increase the frequency of largerprawns or the overall weight of the prawn population raised in pondsfor 3.5 months. In addition to not favoring the development of laggardprawns, grading juveniles using a commercial grading box is difficultbecause the small difference in the sizes of “upper” and “lower”juveniles and the large number of animals needed for stocking. Stockingdensities used in M. amazonicum culture are 5–10 times higher thanthose used for M. rosenbergii (cf. Moraes-Valenti and Valenti, 2010;Valenti et al., 2010). In addition, the difference in weight between thedominant and the stunted morphotypes of M. amazonicum is small,which makes the use of selective harvesting very difficult. A 12-mmmeshnet did not capture only the largest animals, but also a largepart ofthe small ones, which had to be returned to the ponds. Larger meshesare not efficient to remove dominant prawns and berried females.Therefore, grading juveniles and selective-harvesting are more difficultand labor-consumingpractices in the grow-out phase ofM. amazonicumthan in M. rosenbergii.

It seems that grading juveniles and selective-harvesting manage-ment strategies are not advantageous for M. amazonicum grow-out inshort rearing cycles (about 3–4 months). However, studies should bedone to evaluate the effects of these strategies in culturesmaintained for6 to 8 months, which are usedwhen the production strategy is to obtain1 to 2 annual cycles in subtropical and tropical regions (Valenti andTidwell, 2006). Perhaps in these cases, prawns of the smaller fractionand the population remaining in the ponds after selective harvestinghave time to develop, increasing the final frequency of large prawns andproductivity. In addition, studies should be carried out with the aim ofdelaying reproduction in ponds, so that the prawns will allocate moreenergy to growth.

Acknowledgements

We are grateful to FAPESP, CNPq and CAPES for fellowships and forfunding this research.We also thank the staff of the Crustacean Sector,CAUNESP for technical support.

References

Bauer, R.T., 2004. Remarkable Shrimps: Adaptations and Natural History of theCarideans. University of Oklahoma, Norman.

Begon, M., Townsend, C.R., Harper, J.L., 2006. Ecology from Individuals to Ecosystems,4th ed. Blackwell Publishing Ltd, Oxford.

211B.L. Preto et al. / Aquaculture 307 (2010) 206–211

Boyd, C., Zimmermann, S., 2010. Grow-out systems—water quality and soil management.In:New,M.B., Valenti,W.C., Tidwell, J.H., D'Abramo, L.R., Kutty,M.N. (Eds.), FreshwaterPrawns; Biology and Farming. Wiley-Blackwell, Oxford, pp. 239–255.

Daniels, W.H., 1993. Classification of male morphotypes of the freshwater prawnMacrobrachium rosenbergii based upon external morphology and reproductivecondition and description of factors influencing metamorphosis. PhD Thesis, Facultyof Mississipi State University, Mississipi, 282pp.

Daniels, W.H., D'Abramo, L.R., Fondren, M.W., Durant, M.D., 1995. Effects of stockingdensity and feed on pond production characteristics and revenue of harvestedfreshwater prawns Macrobrachium rosenbergii stocked as size-graded juneniles. J.World Aquac. Soc. 26, 38–47.

Holthuis, L.B., 1966. A collection of freshwater prawns (Crustacea Decapoda,Palaemonidae) from Amazonia, Brazil, collected by Dr. G. Marlier. Bull. Inst. R. Sci.Nat. Belg. 42 (10), 1–11.

Karplus, I., 2005. Social control of growth in Macrobrachium rosenbergii (De Man): areview and prospects for future research. Aquac. Res. 36, 238–254.

Karplus, I., Hulata, G., Wohlfarth, G.W., Halevy, A., 1986. The effect of size-gradingjuvenile Macrobrachium rosenbergii prior to stocking on their population structureand production in polyculture. I. Dividing the population into two fractions.Aquaculture 56, 257–270.

Karplus, I., Hulata, G., Wohlfarth, G.W., Halevy, A., 1987. The effect of size-gradingjuvenile Macrobrachium rosenbergii prior to stocking on their population structureand production in polyculture. II. Dividing the population into three fractions.Aquaculture 62, 85–95.

Keppeler, E.C., Valenti, W.C., 2006. Effects of selective harvest of the Amazon Riverprawn, Macrobrachium amazonicum, on pond water, sediment and effluent. ActaLimnol. Brasil. 18 (2), 109–119.

Kutty, M.N., 2005. Towards sustainable freshwater prawn aquaculture—lessons fromshrimp farming, with special reference to India. Aquac. Res. 36, 255–263.

Maciel, C.R., Valenti, W.C., 2009. Biology, fisheries and aquaculture of the Amazon Riverprawn Macrobrachium amazonicum: a review. Nauplius 17 (2), 61–79.

Moraes-Riodades, P.M.C., Valenti, W.C., 2004. Morphotypes in male Amazon Riverprawns, Macrobrachium amazonicum. Aquaculture 236, 297–307.

Moraes-Riodades, P.M.C., Kimpara, J.M., Valenti, W.C., 2006. Effect of the Amazon Riverprawn Macrobrachium amazonicum culture intensification on ponds hydrobiology.Acta Limnol. Brasil. 18, 311–319.

Moraes-Valenti, P., Valenti, W.C., 2010. Culture of the Amazon River prawnMacrobrachium amazonicum. In: New, M.B., Valenti, W.C., Tidwell, J.H., D'Abramo,

L.R., Kutty, M.N. (Eds.), Freshwater Prawns: Biology and Farming. Wiley-Blackwell,Oxford, pp. 485–501.

Moraes-Valenti, P., Preto, B.L., Morais, P.A., Valenti, W.C., 2010. Effect of density onpopulation development in the Amazon River prawn Macrobrachium amazonicum.Aquat. Biol. 9, 291–301.

New, M.B., 2002. Farming Freshwater Prawns. A Manual for the Culture of the Giant RiverPrawn (Macrobrachium rosenbergii). FAO Fisheries Technical Paper, No. 428. FAO,Rome.

New, M.B., 2005. Freshwater prawn farming: global status, recent research and glanceat future. Aquac. Res. 36, 210–230.

Pettovello, A.D., 1996. First record of Macrobrachium amazonicum (Decapoda,Palaemonidae) in Argentina. Crustaceana 69, 113–114.

Sokal, R.R., Rolf, F.J., 1995. Biometry, 3a ed. Freeman, New York.Solorzano, L., 1969. Determination of ammonia in naturalwaters by the phenythypochlorite

method. Limnol. Oceanogr. 14, 799–801.Tidwell, J.H., Coyle, S.D., Bright, L.A., Vanarnum, A., Weibel, C., 2003. The effects of size

gradindand lenghtof nurseryperiodongrowthandpopulationstructureof freshwaterprawns stocked in temperate zone ponds with added substrates. Aquaculture 218,209–218.

Tidwell, J.H., Coyle, S.D., Dasgupta, S., 2004a. Effects of stocking different fractions ofsize graded juvenile prawns on production and population structure during atemperature-limited grow-out period. Aquaculture 231, 123–134.

Tidwell, J.H., Coyle, S.D., Dasgupta, S., Bright, L.A., Yasharian, D.K., 2004b. Impact ofdifferent management technologies on the production, population structure andeconomics of freshwater prawn Macrobrachium rosenbergii culture in temperateclimates. J. World Aquac. Soc. 35, 498–505.

Tidwell, J.H., D'Abramo, L.R., Coyle, S.D., Yasharian, D.K., 2005. Overview of recentresearch and development in temperate culture of the freshwater prawn(Macrobrachium rosenbergii De Man) in the South Central United States. Aquac.Res. 36, 264–277.

Valenti, W.C., Tidwell, J.H., 2006. Economics and management of freshwater prawnculture in Western Hemisphere. In: Leung, P.S., Engle, C. (Eds.), Shrimp Culture:Economics, Market, and Trade. Oxford, Blackwell Publishing, pp. 261–276.

Valenti, W.H., New, M.B., Salin, K.R., Ye, J., 2010. Grow-out systems—monoculture. In:New, M.B., Valenti, W.C., Tidwell, J.H., D'Abramo, L.R., Kutty, M.N. (Eds.), FreshwaterPrawns; Biology and Farming. Wiley-Blackwell, Oxford, pp. 154–179.