Aquaculture Research. 1996. 27, 277-282

Pond production of Penaeus monodon in relation tostocking density, survival rate and mean weight atharvest in East Java, Indonesia

A M Hariati,' D G R Wiadnya,' M Sukkel,^ J H Boon,^ & M ) C Verdegem^'Universitas Brawijaya. Fakultas Perikanan. Malang. Indonesia, and ^Department of Fish Culture and Fisheries. Institute of

Animal Science. Wageningen Agricultural University. Wageningen. The Netherlands

Correspondence: J H Boon. Wageningen Agricultural University. Department of Fish Culture and Fisheries. PO Box 338. 6700 A.H.

Wageningen. The Netherlands

Abstract

The relationships between Penaeus monodon produc-tion and three crop characteristics in 107 ponds onnine shrimp farms in East Java were studied. Overalldifferences of production (Mt ha"' year"'), survival rate(%), stocking density (number m"') and mean weightat harvest (g) hetween regions and between farms weresignificant, while the difference of production hetweenfarms was also significant within regions. Overallanalysis revealed that production was positivelycorrelated with survival rate, stocking density andmean weight at harvest, while there was a negativecorrelation hetween stocking density and survivalrate. Results imply that more attention should he paidto improving shrimp survival. The higher on-farmproduction in South East Java is linked to highersurvival rates and higher post-larvae stocking densitiesthan in North West and North East Java,while similarindividual weights at harvest to North West East Javaare reached. In this context, the relationship hetweencoastal estuadne water quality and yield needs furtherinvestigation. Other parameters which need furtherinvestigation are farm management, post-larvae originand duration of the culture period.

introduction

Between 1992 and 1994, Penaeus monodon harvestsfrom tamhaks in East Java, Indonesia, declined drama-tically (Hariati, Gede, Wiadnya, Prajitno, Sukkel, Boon& Verdegem 1995). A major cause of the decline in

tambak production is supposed to be poor waterquality, and associated infectious and non-infectiousdiseases of unknown aetiology. Therefore, some farm-ers shifted production from P. monodon to P. merguiensis,which is said to he more resistant to poor environ-mental conditions. Other farmers applied antibacterialdrugs (Sunaryanto & Mariam 1986) or vaccinesagainst vihriosis (Itami, Takahashi & Nakamura 1989;ltami, Takahashi, Yoneoka & Yan 1991; Song & Sung1990: Sung, Song & Kou 1991). Because of thedisappointing results and high treatment costs of thesemeasures, most farmers have to rely on more basicmanagement measures, such as increased stockingdensities, to improve tambak shrimp production. Thepresent paper evaluates the effectiveness—in terms ofyield—of changing the stocking density or cultureperiod. Therefore, stocking density, survival rate,mean shrimp weight at harvest and production of 107tambaks on nine farms located in three different areasin East Java, Indonesia, were monitored during onecomplete production cycle.

Material and methods

Farms

Two farms (Fig. 1, farms 1 and 2) in North West (NW)East Java, three (Fig, 1, farms 3-5) in North (N) EastJava and four farms (Fig. 1, farms 6-9) in South (S)East Java were selected, based on the availability ofreliable pond production records and the willingnessof managers or owners to cooperate. In total, 107 Rmonodon mono-culture ponds were monitored, with a

© 1996 Blackwell Science Ltd. 277

Shrimp production in East Java A M Hariati et al. Aquaculture Research, 1996, 27, 277-282

minimum of six ponds per farm, AU farm ponds weresupplied with estuarine water using tidal action; thesame channels and gates were used for water intakeand drainage. Water exchange takes place irregularly, andsalinity varies with season and with the mbdng patternof fresh and marine water in the adjacent estuary.

Parameters

Data collected were total tambak production (Mt ha"'year-'), pond surface area, number of post-larvae (PL)stocked and the mean number of shrimps per kilogramat harvest. AH the data collected refer to the mostrecent crop (late 1993 for farms 1. 2. 3. 6 and 7. andearly 1994 for farms 4, 5, 8 and 9; Fig. 1). Annualproduction was calculated assuming two crops peryear, which is common practice in East Java.

Calculations and statistics

Parameters derived from the field observations andused in the statistical analysis were: production (Mt

ha"' year-') assuming two crops per year; stockingdensity (PL m^̂ ); survival rate (%) calculated as; (numberof shrimp harvested/number of PL stocked) x 100; andmean shrimp body weight at harvest (g), calculatedusing the number of shrimp in 1 kg at harvest.Influences of farms or regions on the parametersinvolved were analysed using a one-way ANOVA. Whenregional influence was significant, difference (s)between regions were analysed using LSD. Overallrelationships between production and survival rate,stocking density and mean weight at harvest, respec-tively, were investigated using linear or curvelinearregression analysis. For all statistics, the STATISTIXprogram (Statistix 1985) was used.

Results

A review of estimated parameters for 107 tambakponds, clustered in groups of six to 20 per farm, is givenin Table 1. The range of the mean farm production perfarm was 9.4-24,1 Mtha-' year"', while ranges ofmeans of stocking density, individual weight and

Java sea

Central Java

Farm:12345

District:Tub anGresikSifubondoProbolinggoProbolinggo

Farm;6789

District:LumajangLumajangLumajangMalang

Indian Ocean

Figure 1 Location of farms monitored in East-Java,

278 © 1996 Blackwell Science Ltd, Aguflcu/ture Research, 27, 277-282

Aquaculture Research, 1996, 27, 277-282Shrimp production in East Java A M iiariali et al.

survival rate were 2 6.1-54.9 PL m-, 20.4-31,5 gand52.5-80.6%, respectively. The stocking density of farm2 was nearly half that of other farms. Mean shrimpbody weight at harvest of farm 8 (S East Java) and farm3 (N East Java) were lower than for all the other farms.

All production parameters differed between regionsand farms (Table 2) (ANOVA, P < 0,05). In S East Java,yields were higher than in NW and N East Java(Table 3) (LSD, P < 0,05), while yields in NW and NEast Java were similar (P > 0.05). On average, thestocking density in S East Java was higher than in NWand N East Java, being lowest in the NW region (Table3,LSD, P < 0.05). Nevertheless, looking more closely atTable 1, stocking densities are between 41 and 48individuals per square metre, except for farms 2 and9, The real difference in regions appeared to hesurvival, and hence, production. Survival rate in S andNW East Java was higher than N East Java (Table 3)(LSD, P < 0.05). Furthermore, the mean weight at

harvest in S East Java was higher than in N East Java(Table 3) (LSD, P< 0.05).

When all data from the nine farms were analysedtogether, models chosen for regression analysis revealedsignificant linear regressions between production andsurvival rate and mean weight at harvest, respectively',while there was a quadratic relationship betweenproduction and stocking density (Fig, 2). Stockingdensity was negatively related to survival rate in alinear regression (Fig. 2) (P < 0.01). The relationshipsbetween mean weight at harvest and both stockingdensity and survival rate were not significant.

Data for the various within farm regressions aregiven in Table 4. Analysis by farm yielded a significantregression between production and survival rate fornearly all farms, while the regressions betweenproduction and both stocking density and meanweight at harvest, and between survival rate andstocking density, were only significant on a few farms.

Table 1 Farm means for stocking density (STD), mean weight at harvest (WEI. g). survival rate (SR. 'X.I and yield (PROD, Mth a ' year"'): standard deviations are given

Farm

1

234567

89

Overall meansTotal ponds

Region

NWNWNNNSSSS

Numberof ponds

8

768

1920208

11

107

Mean

STD

42.526.146.845.441.4

47.043.748.054.9

43.97

WEI

27.925.620.4

23.222.227.325.520.831.5

24.95

SR

53.180.652.557.3

54.075.668.072.370.1

64.84

PROD

12.510.39.4

11.310.118.214.4

14.524.1

13.87

Standard deviation

STD

2.19.1

14.4

3.83.3

10.03.82.31.1

WEI

3.13.42.62.03.24.35.7

1.63.3

SR

5.012.212.811.1

15.219.313.49.84.8

PROD

1.43.01.81.72.72.83.22.11.6

Table 2 Results of ANOVA of stocking density (STD), mean weight at harvest (WEI. g). survival rate (SR. %) by region and by fcirm

RegionFarm

DFbetween

28

STD

F

15.611.01

P

<0.001<0.001

WEI

F

11.138.33

P

<0.001<0.001

SR

F

13.7

6.0

P

<0.001<0.001

PROD

F

44.636.8

P

<0.001<0.001

© 1996 Biackwell Science Ltd,/l^uacuftureReseardi. 27, 277-282 279

Shrimp production in East Java A M Hariati et al. Aquaculture Research. 1996, 27, 277-282

Table 3 Region means for stocking density (STD). mean weight at harvest (WEI. g), survival rate (SR. %) and yield (PROD. Mth a ' year ' ) . Means in one column followed by a different letter are differ significantly (least significant difference)

NW East JavaN East JavaS East Java

Mean

STD

34.84=^43.35''47.50»

WEI

26.85"22.12"26.61"

SR

65.95"54.54"71.56"

PROD

11.48-10.26"17.50"

Standard deviation

STD

10.757.357.45

WEI

3.592.995.45

SR

17.0514.2214.82

PROD

2.612.494.50

r » 0.67;/> < 0.01

, ' ' ' • »%•*•*••*

20 30 40 SO 60 70 80 90 100 110

SR (%)

4. M A | .7*« O 1.1 + MA t.3 • M 7 >.« O r.«

V = -1.5 + 0.53X-0.004X^r= 0.36; P< 0.01

• • • • . •

V •

10 20 30 40 SO 60 70 80

STD (PLs M2-')

30

WEI (g)

V'=0.44 + 0.55Xr = 0.55; P < 0.001 t to

100

90

ITCO

y = 93.02-0.82Xf =-0.33; P< 0.01

•.« ** J-

10 20 30 40 50 60 70 80

STD (PLs M2-')

Figure 2 Regression analysis of shrimp production from 107 tambaks in East Java; STD. stocking density (number per m^);WEI. mean weight at harvest (g); SR. survival rate (%); PROD, yield (MT ha ' year') .

the relationship between production and stocking areas, which were clearly observed in the presentdensity being positive or negative. study, can depend on numerous factors: geographical

differences (Lee & Wickins 1992).managementpractices(Subosa & Bautista 1991), water quality (Chakraborti,

Discussion Ravichandran. Haider. Mandal & Sanfui 1985) and theorigin of the PL (Lutz & Wolters 1989). The data

Differences in tambak production between farms and available do not allow analysis of between-farm

280 ©1996B\ackwenScieaceUd. Aquaculture Research. 27, 277-282

Aquaculture Research, 1996. 27, 277-282 Shrimp production in East Java h U Hariati et al.

Table 4 Coefficients of regression (b) and correlation (r) between production parameters: abbreviations used are similar as forprevious tables, for location of farms, see Fig. 1

Farm

1

23456789

PROD versus SR

b

0.1169

0.14200.17850.07300.09520.14220.16350.1623

-0.1430

r

0.80"*0.60"*0.66*0.350.660.93***0.91*"0.77**0.43

PROD versus STD

b

-0.2219-0.22330.02160.23440.0441

-0.2511-0.27670.34760.7914

r

0.78***0.270.030.71*0.310.570.330.380.55*

PROD versus WEI

b

0.13970.27770.1797

-0.3039-0.24860.2145

-0.04040.06500.4162

r

0.210.50"0.410.350.340.250.040.040.87***

SR versus STD

b

-1.8095-0.84080.6060

-0.4817-0.3838-1.7626-1.68000.0476

-3.1992

r

0.93***0.240.260.360.430.610.360.010.73***

*P<0.10.*'/'<0.05."*P<0.01.

production differences on the hasis of managementpractices and PL quality. However, some observationsare possible on geographical differences and waterquality. Tambak production of P. monodon in the S EastJava was higher than in N W and N East Java. Farms inthe South were constructed after 1986, while thetambak system in NW and N East Java is centuries old(Hariati et al. 1995). Furthermore, demographicpressure in the South is lower than in the North. Thesea along the north coast of East Java is less than40 m deep in most places, and relatively isolatedfrom surrounding oceans. The whole system can beconsidered as an estuary, receiving waste waters fromcities, industries and agriculture in one of the world'smost densely populated regions. The sea along S EastJava has a good connection with the Indian Ocean, andis less polluted than N W and N East Java coastal waters.Further research is required to determine if the waterentering the ponds in the North is of poor quality, andwhether this causes the difference in productionbetween farms in the South and the North,

Most farmers favour increasing stocking density asa measure to increase yield. This may be a successfulmeasure up to a limit. The overall quadratic relation-ship between production and stocking density (Fig. 2)indicates there is an optimal stocking density of66 PL m-^ At higher stocking densities, yields willdecrease. Nevertheless, most farmers stock less than66 PL m" .̂ Because survival rate decreases with in-creasing stocking density, and yield depends on bothsurvival rate and stocking density, the optimal stocking

density vrtll decrease when survival rates are above theoverall mean of 65% (Table 1). The negative slope forthe regression of production and stocking density,observed on farm 6 in S East Java (Table 4), which useda stocking density of 47 PL m'̂ and obtained a survivalrate of nearly 76% (Table 1), suggests that the optimalstocking density at this farm is well below 66 PL m •'.This suggests that improved survival (by improvedmanagement or PL quality) may be more beneficial toenhance production than increasing stocking density(Table 1). More observations are needed to calculate aquadratic regression for production and stockingdensity, and hence, the optimum stocking density perfarm. Assuming 9 5% confidence limits, the minimumnumber of observations needed to obtain a significantrelationship is 30.

The positive relationship between production andmean weight at harvest can be explained by the customto harvest when shrimp growth is impaired. Farmersestimate growth per pond by fortnightly weighing andcounting randomly taken shrimps samples. If growthis impaired below 2 5 g mean weight, shrimps are firsttreated with an antimicrobial drug, assuming abacterial infection being the cause. If growth does notimprove thereafter, the pond is harvested. Ponds arealso harvested if growth is impaired ahove 2 5 g meanweight.

Yield increases with increasing survival rate. Bettersurvival can be obtained by stocking high-quality PLand preventing disease outbreaks. In general, it canbe stated that improved general pond management

© 1996 Biackwell Science Ltd,/IguacuitureResearch, 27, 277-282 281

Shrimp production in East Java A M Hariati et al. Aquaculture Research. 1996, 27, 277-282

reduces the frequency of disease outbreaks (Kongkeo

1994),

In conclusion, tambak yield of P. monodon mono-

culture in East Java is directly linked to survival rate

and individual weight at harvest, the relationship with

stocking density being less strong. The higher on-farm

production in S East Java is linked to higher survival

rates and higher PL stocking densities than in NW and

N East Java, while similar individual weights at harvest

are reached, as in NW East Java, In this context, the

relationship between coastal estuarine water quality

and yield needs further investigation. Other parameters

which need further investigation are farm management.

PL origin and duration of the culture period.

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Hariati A,M,, Wiadnya R,. i'rajitno A,, Sukkel M,, Boon J,H,& Verdegem M.CJ, (19 9 5) Recent developments of Penaeusmonodon and P. merquiensis culture in East Java, AquacultureResearch 26, 819-829,

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282 © 1996 Blackweli Science Ltd, AquacultureRcseardi, 27. 277-282