Stocking densities for nursery phase culture
of the freshwater prawn Macrobrachium
H.L. de A. Marques)
, J.V. Lombardi, M.V. BoockFisheries Institute, Sao Paulo State Agricultural Department, A˜ Õ. Francisco Matarazzo 455,
05001-900 Sao Paulo, SP, Brazil˜
Accepted 22 December 1999
Effect of stocking density on growth, biomass increase and survival of postlarvae of Macro-brachium rosenbergii were evaluated in cages fixed inside an earthen pond. In the primary
nursery phase, newly metamorphosed postlarvae PL were stocked for 20 days at densities of 2,
y1 Ž .
4, 6, 8 and 10 PLs l . In the secondary phase 60 days , the densities tested were 100, 200, 300, 400, 600 and 800 PLs my2. Prawns were fed with a 35% protein commercial pellet. Survival,
final mean weight and average weight gain were significantly lower P-0.05 in high densities
of the primary phase, whereas biomass increase was significantly higher P-0.05 . In the
secondary phase, final mean weight and average weight gain were significantly higher P-0.05
. y2 y2
and P-0.01, respectively for densities of 100 and 200 PLs m than for density of 800 m .
Ž . y2
Biomass increase was significantly higher P-0.01 at densities of 400, 600 and 800 PLs m , when compared to densities of 100 and 200 my2, whereas survival differences were not
significant. High-density nursery culture of M. rosenbergii in cages seems to be feasible, in order to reduce the costs normally found in conventional nursery systems.q2000 Elsevier Science B.V. All rights reserved.
Keywords: Prawns; Marobrachium rosenbergii; Cages; Nursery; Growth; Survival
E-mail address: firstname.lastname@example.org H.L. de A. Marques .
0044-8486r00r$ - see front matterq2000 Elsevier Science B.V. All rights reserved.
The culture of Macrobrachium rosenbergii in Brazil is generally practiced through semi-intensive system, by means of stocking ponds with postlarvae at densities varying
y2 y1 y1 Ž
from 5 to 10 prawns m . Yields are from 1000 to 2500 kg ha year Valenti,
1993 . The main constraint to culture intensification has been the larger investment amount, due to the construction of nursery tanks and ponds and the expense of handling and transferring juveniles from nurseries to grow-out ponds.
Cage aquaculture is a viable alternative to traditional techniques of rearing, due to its
practicability and, mainly, low costs Beveridge, 1996 . Successful nursery and grow-out culture of M. rosenbergii in cages were already tested in India by Panicker and Kadri
Ž1981 , who did not find significant differences between weight increases of juveniles.
reared in conventional concrete tanks and in cages placed in dams. Other research was
carried out in Thailand Menasveta and Piyatiratitvokul, 1982; Singholka and
Suk-. Ž . Ž
sucheep, 1982 , in Hawaii Stanley and Moore, 1983 , in Israel Sagi et al., 1986; Gofer,
. Ž .
1991 and in Bangladesh Angell, 1994 .
In Brazil, Marques et al., 1996 stocked M. rosenbergii postlarvae in cages at low
densities 50 and 100 PLs m during 60 days, recording better growth and survival than those reported in the literature for postlarvae nursed in concrete tanks. On the other hand, the same authors reported that the increase of stocking densities resulted in a significant reduction in growth but no significant differences in survival. This encour-ages the use of higher stocking densities in order to reduce the number and the size of cages necessary to promote nursery culture on a commercial scale. Therefore, the purpose of this study was to test the effects of high-density on growth and survival of
M. rosenbergii postlarvae reared in cages in two phases: primary nursery 20 days and
secondary nursery 60 days .
2. Materials and methods
This study was conducted in the Aquaculture Experimental Station of the Sao Paulo
˜State Fisheries Institute in Pindamonhangaba, Sao Paulo State, southeastern Brazil.
Ž . Ž .
Cages were composed of prismatic iron frames of 1.0 m length =0.50 m width =0.70
m depth , covered with a polyethylene net of 1 mm mesh and fixed through stakes in a single earthen pond of 0.24 ha. Each cage was submerged to be at least 50 cm above the pond bottom and with 30 cm of the sides above the water level. Thus, 40 cm of the sides were immersed and there were 200 l of useful volume inside each cage.
The experiments were carried out in three different periods Jan–Feb 1997, Dec
1997–Jan 1998 and Feb–Mar 1998 for the primary nursery phase and two periods
ŽFeb–Apr 1997 and Mar–May 1998 for the secondary one. As the environmental.
conditions water temperatures, pH and dissolved oxygen were quite similar between the periods in each phase, it was possible to group the data in order to analyse the results. Therefore, the number of replicates was different for each treatment in both
Ž . Ž
In the primary nursery phase, early metamorphosed postlarvae PLs 0.011"0.006
. Ž .
g "SE were acquired from a commercial hatchery and acclimatized during 18 h in two 1400-l cages at a density of 4 PLs ly1. Afterwards, the PLs were stocked in cages
Ž . y1
for 20 days primary nursery phase at five densities: 2, 4, 6, 8 and 10 PLs l . A polyethylene screen of 40=40 cm and 1.0 mm mesh was fixed vertically at the middle of each cage as an additional surface and shelter. This same procedure was followed for the three experimental periods.
The postlarvae harvested in the primary phase, weighing 0.053"0.009 g, were mixed together and utilized in the secondary nursery phase. They were placed in cages for 60 days, according to 6 different density treatments: 100, 200, 300, 400, 600 and 800 PLs my2. Density was based only on cage bottom, which was 0.5 m2 for each cage. In
this phase, the cages did not contain the polyethylene screens.
Prawns were fed once a day, in the afternoon, with 35% protein commercial pellets that were specially processed and of balanced composition for freshwater prawns. The amount of feed was 50% and 10% of the stocked biomass in the primary and secondary phases, respectively. In order to adjust the amount of feed supply, biometric data were collected after 30 days of nursery culture for samples of at least 10% of the prawns stocked in each cage.
Water temperatures maximum and minimum , pH and dissolved oxygen were
frequently monitored inside all the cages. A paddle wheel aerator 0.5 hp was installed in the pond and activated mainly at night, in order to maintain high dissolved oxygen levels and adequate water circulation.
Cages were harvested at the end of each phase, and the weight and survival of prawns
were recorded. Average weight gain final minus initial mean weight , final mean
weight and total biomass increase final minus initial biomass of prawns were analyzed by one-way ANOVA followed by F-test. Means were compared by Duncan’s new
Ž . Ž .
multiple range test DNMR Zar, 1996 . Percent survival data were arcsin transformed before analysis by one-way ANOVA. Homogeneity of variance was assessed using Bartlett’s test. In all tests, means were considered different when at least at P-0.05.
There were no major differences in measured water quality parameters between cages, and thus between treatments. All the measured variables were within acceptable
limits for freshwater prawn culture New and Singholka, 1985 . In the primary nursery phase, minimum water temperatures inside the cages ranged from 23.58C to 27.08C
Žmean of 25.3"1.38C. Ž"SE , whereas maximum water temperatures varied from 25.0.
Ž . y1
to 33.08C mean of 29.6"2.58C . Dissolved oxygen ranged from 7.2 to 8.4 mg l
Žmean of 7.8"0.4 mg ly1.and pH varied from 8.5 to 9.3 mean of 9.0Ž "0.3 . In the.
secondary phase, minimum temperatures ranged from 19.08C to 28.08C mean of
Effects of stocking density on growth and biomass increase during the primary phase of nursery culture in M. rosenbergii in cages
Values with at least one equal superscript letter are not significantly different P)0.05 . Density treatments Average weight gain Final mean weight Total biomass increase Survival
8 0.031"0.010 0.042"0.010 30.14"11.85 78.2"11.4
b,c b,c b b
10 0.032"0.005 0.043"0.005 31.23"13.15 62.8"16.5
Ž . Ž . Ž . Ž .
ANOVA F-test 3.78 P-0.05 3.78 P-0.05 3.04 P-0.05 3.09 P-0.05
There were significant differences P-0.05 in prawn growth and survival between
the densities tested for the primary Table 1 . Final mean weight and average weight gain were significantly lower, whereas total biomass increase was significantly higher in cages with density of 8 and 10 PLs ly1
than those of 2 PLs ly1
. Survival was significantly higher at the density of 2 PLs ly1 than at 6 or 10 PLs ly1. No significant differences were observed between prawn growth and survival at 4, 6, 8 and 10 PLs ly1 densities.
For the secondary phase, differences in survival among densities were non-significant
ŽP)0.05. ŽTable 2 . At harvest, final mean weight and average weight gain were.
Ž . y2
significantly higher P-0.05 and P-0.01, respectively at 100 and 200 PLs m
densities than the highest one 800 PLs m . On the other hand, total biomass increase
Ž . y2
was significantly higher P-0.01 at densities of 400, 600 and 800 PLs m , when
compared to lower ones 100 and 200 PLs m .
As a general rule, for both primary and secondary phases, there was an inverse relationship between final mean weight and, whereas total increase gain showed a direct
Secondary nursery performance of M. rosenbergii in cages
Values with at least one equal superscript letter are not significantly different.
Density treatments Average weight gain Final mean weight Total biomass increase Survival
relationship with density. Survival also tended to be higher in low densities, but only for the primary nursery phase.
Nursery culture of M. rosenbergii postlarvae in cages at high densities seems to be feasible if these results are compared to those obtained in conventional nurseries. Cohen
Ž . 3
and Ra’anan 1989 , who stocked postlarvae in 50 m concrete tanks at a density of 3.8
PLs l over 16 days, reported a weight gain of 0.02 g mean weight increasing from
0.01 to 0.03 g , with survival of 86.5%. In the present experiment, average weight gains were 0.04 and 0.05 g and survivals were 87.9% and 62.8% for the 4 and 10 PLs ly1
densities, respectively primary phase .
Final mean weights of prawns recorded here after the secondary phase were lower
Ž . Ž
than those reported by Valenti 1996 for natural earthen nurseries final mean weight of about 1 g with around 80% of survival after 60 days of nursery culture at 100–200 PLs
y2 . Ž .
m densities . Menasveta and Pyatiratitvokul 1982 also found that the growth of M.
rosenbergii in cages in grow-out phase was lower than those observed in ponds and ditches, although survival was significantly better in cages. The results observed here
agree with those related by Ang et al. 1992 to the grow-out phase of prawns in cages. They reported that a stocking density of 10 PLs my2 provided better growth than 20 or
50 PLs my2, although final biomass was highest at the greatest stocking density.
Nevertheless, these authors reported greater survival at lower densities, which was not observed here.
Survival of prawns cultured in cages during 60 days secondary phase seems not to be affected by increasing densities, despite the lower individual mean weights. However, it is not known if small juvenile prawns harvested from the high-density nursery, and then transferred to grow-out ponds at normal densities, can recover the lost weight and
reach commercial size at the normal time of growing 3–4 months in southeastern
. Ž .
Brazil . Malecha et al. 1989 state that small-sized prawns have an inherent capacity for compensatory growth in the absence of dominant males. They recommend using
high-density nursery ponds 1000 PLs m provided with shelters in order to reduce the competition for space. An important requisite in this case seems to be stocking grow-out ponds with juveniles cultured at the same density, since the presence of larger prawns in the same pond can suppress the growth of the small ones.
These data suggest that stocking post-larvae in cages, at high densities, 10 PLs l
materials for nets and frames need to be considered in order to reduce the costs and allow for application to commercial scale.
This research was partially supported by the Brazilian National Council of Scientific
and Technological Development CNPq Project 301046r77-8 and the Sao Paulo State
Research Support Foundation FAPESP Project 96r10083-3.
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