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Stocking densities in cage rearing of Amazon river prawn (Macrobrachium amazonicum) during nursery phases
Aquaculture 307 (2010) 201–205
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Aquaculture j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / a q u a - o n l i n e
Stocking densities in cage rearing of Amazon river prawn (Macrobrachium amazonicum) during nursery phases Helcio Luis de Almeida Marques a,⁎, Julio Vicente Lombardi a, Margarete Mallasen b, Helenice Pereira de Barros b, Marcello Villar Boock c a
Centro de Pesquisas em Aquicultura, Instituto de Pesca, Agência Paulista de Tecnologia dos Agronegócios, Secretaria de Agricultura do Estado de São Paulo, Av. Francisco Matarazzo, 455, 05001-900, São Paulo, SP, Brasil Centro APTA do Pescado Continental, Instituto de Pesca, Agência Paulista de Tecnologia dos Agronegócios, Secretaria de Agricultura do Estado de São Paulo, PO Box 1052, 15025-970, São José do Rio Preto, SP, Brasil c Pólo APTA Nordeste Paulista, Agência Paulista de Tecnologia dos Agronegócios, Secretaria de Agricultura do Estado de São Paulo, PO Box 58, 13930-070, Mococa, SP, Brasil b
a r t i c l e
i n f o
Article history: Received 16 April 2010 Received in revised form 24 July 2010 Accepted 28 July 2010 Keywords: Biomass Freshwater prawns Growth Juvenile Productivity Survival
a b s t r a c t Amazon river prawn (Macrobrachium amazonicum) is widely distributed along Brazilian rivers, being one of the native species with a major cultivation potential. This study evaluated stocking densities during primary and secondary nursery phases for M. amazonicum in cages, regarding survival, growth, biomass, food conversion and productivity. The experiment was carried out in 12 cages of 0.5 m2 (iron frames recovered with polyethylene mash) placed inside of a 1500 m2 earthen pond. Early metamorphosed postlarvae (PL) (0.009 ± 0.006 g) were stocked for 28 days (primary nursery phase), at densities of 4, 6, and 8 prawns L−1. In the secondary nursery phase (62 days), densities were 200, 400 and 800 prawns m− 2 (0.12 ± 0.01 g). Prawns were fed commercial pellets (35% crude protein). Water quality parameters were within the adequate range for freshwater prawn culture. In the primary nursery phase, the productivity for density of 8 PL L−1 was two times greater compared to 4 PL L−1 (6.17 and 3.35 juveniles I L−1, respectively) and differed significantly (P b 0.05). In the secondary nursery phase, mean survival was above 95% and did not differ significantly, while mean weight differed (P b 0.05) for the densities of 200 (0.44 g) and 800 (0.36 g) prawns m−2. The highest biomass (143.6 g) was registered at 800 prawns m−2 density and differed significantly (P b 0.01) from lower densities. The productivity of juveniles II also differed significantly among densities, being about four times greater at 800 prawns m−2 compared to lower densities. Net income was positive only at densities greater than 400 prawns m−2, being highest at a density of 800 prawns m−2. Thus, on an experimental basis, the nursery system for M. amazonicum at high densities in cages showed to be viable. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Freshwater prawn culture in Brazil is almost completely restricted to the exotic species, Macrobrachium rosenbergii. There are however, native species of the same genus with culture potential such as M. acanthurus, M. carcinus and Macrobrachium amazonicum (Valenti, 2007). Although there is no evidence of any negative ecological impact of M. rosenbergii, there are benefits to use local species rather than exotic ones for both genetic and environmental reasons (Araujo and Valenti, 2007). Among native species, M. amazonicum has the greater potential for culture due to biological characteristics (Kutty et al., 2000). The biological features of this species are being studied in Brazil since the 1980s, but only recently technological aspects ⁎ Corresponding author. Tel.: +55 11 3871 7535. E-mail addresses: [email protected] (H.L.A. Marques), [email protected] (J.V. Lombardi), [email protected] (M. Mallasen), [email protected] (H.P. de Barros), [email protected] (M.V. Boock). 0044-8486/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2010.07.035
regarding its farming are being developed (Kiyohara, 2006; MoraesValenti and Valenti, 2007; Preto et al., 2008). Freshwater prawn culture is mainly practiced by small farmers. Thus, it is necessary to develop culture technologies that are simple and relatively low cost, in order to make this activity more profitable. Among alternative culture technologies, the use of cages during both primary and secondary nursery phases have been shown to be viable for the culture of the giant river prawn, M. rosenbergii (Marques et al., 2000). According to the same authors, the easy handling and the possibility of using bodies of water of good quality, such as lakes, ponds and even fish farming ponds to install cages, are some of the advantages of using such a system. Kiyohara (2006) studied the use of cages in the nursery phase of M. amazonicum, at stocking densities varying between 20 and 160 prawns m−2, and concluded that productivity can be higher even at higher densities. Therefore, it might be assumed that stocking densities higher than 160 prawns m−2 may be used during primary and secondary nursery phase. The present study aims at evaluating
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2. Material and methods
Prawns were fed as in the primary nursery phase. The experiment lasted for 62 days, at the end of which all the prawns were individually counted and weighed to determine the performance parameters aforementioned.
2.1. Local and experimental structure
2.5. Partial budget analysis
The experiment was carried out in cages installed inside a 1500 m2 earthen pond located at the Pindamonhangaba Aquaculture Research Center, Fisheries Institute, SP, Brazil (22°55′50″S; 45°27′22″W). The same pond was also being used for rearing reproducers of the noncarnivorous fish Prochilodus lineatus (500 g of mean weight), at a density of 1 fish per each 4 m2. A paddle wheel aerator (0.5 HP) was activated nightly from 19:00 to 6:00 h to assure adequate water circulation and prevent stratification. Cages measuring 70 (height) × 100 (length) × 50 cm (width) built with polyethylene mesh (0.7 mm wide) and iron frames, were used as primary and secondary nurseries. Substrates, made of four 40 × 40 cm polyethylene screen pieces, were fixed vertically to the walls inside the cages in order to increase the available space for prawns. The cages were tied to stakes, suspended about 30 cm from the bottom of the pond and about 40 cm immersed in the water. This set up resulted in primary and secondary nurseries of 200 L volume and 0.5 m2 useful area, respectively. Last, the cages were also covered with polyethylene screen to avoid predators and prawn escape.
A partial budget analysis (Shang, 1990) was performed to evaluate the economic feasibility of increasing stocking densities of M. amazonicum during the secondary nursery phase in cages. In this analysis, only the costs and incomes that varied with increasing densities were considered (juveniles, feed, labor and package). The partial budget was based in a 0.5 m2 cage; it was assumed that the cages were stocked with 30 day old-juveniles, costing US$ 0.028 per unity and estimated that the sale price was US$ 0.05 per unity for a 90 day old-juvenile. The interest rate considered was 0.7% per month. The net income was calculated according to the following expression:
the performance of M. amazonicum cultivated at different densities in cages, during primary and secondary nursery phases.
2.2. Water parameters Temperature (a maximum and minimum thermometer Incoterm), dissolved oxygen (Yellow Springs Instruments 550A), pH (Bernauer F-1002) and conductivity (Bernauer F-1000) were measured daily in the morning, at 30 cm depth, in the surrounding cage area. Water transparency was measured early afternoon using a Secchi disk. Samples of water were collected bi-weekly, at the water sub-surface near the cages, to determine alkalinity, total ammonia (N–NH3 + N– NH+ 4 ), nitrite (N–NO2), nitrate (N–NO3) and total phosphorous (total P), All the analyses were carried out according to APHA (2005).
NI = TR−ðVC + IcÞ; in which NI = net income, TR = total revenue from prawn sales, VC = variable costs and Ic = interests on variables costs. 2.6. Statistical analysis Prawn performance data were analyzed by Shapiro–Wilks and Bartlett tests, to assess normality and homocedasticity respectively. As these conditions were satisfied, means were subjected to an analysis of variance (ANOVA) (Zar, 1999). When significant differences were observed among means (P b 0.05), Tukey test was applied. Values expressed as percentages were square root arcsine transformed prior to analysis, while they are presented as non-transformed for easier review. Regressions were performed using all the values obtained in each replicate. 3. Results 3.1. Water parameters
2.3. Primary nursery phase Newly metamorphosed M. amazonicum postlarvae (PL), originated from an experimental laboratory, were stocked in three 1400 L cages similar to the ones described earlier, placed in the same pond, where they were acclimated for a period of 72 h. Afterwards, the PL (0.009 ± 0.006 g) were randomly distributed in 12 primary nurseries, at densities of 4, 6 and 8 PL L−1. A completely randomized design with three treatments (densities) and four replicates (cages) was used. Commercial pellets (35% crude protein), were supplied to prawns twice a day, in the morning and late afternoon, at a daily rate of 10% of the estimated biomass in the cages. After 15 days, the prawns were measured to check growth rate and to adjust the amount of feed to be supplied. Nurseries were harvested 28 days after stocking and the prawns were individually counted and weighed to determine survival rate, mean weight, biomass, food conversion rate (FCR) and productivity (juveniles I L−1). 2.4. Secondary nursery phase Only the largest juveniles from the primary nursery phase were selected and assigned to the secondary nursery, in order to standardize the size of animals and use prawns with a higher growth potential. The juveniles (0.12 ± 0.01 g) were randomly distributed in 12 cages, at the densities of 200, 400 and 800 prawns m−2. A completely randomized design with three treatments (stocking densities) and 4 replicates (cages) was used. The stocking densities were based on the cage net bottom area.
The lowest water temperature value registered during the experiment was 17 °C. Dissolved oxygen presented higher values during the secondary nursery phase (4.11 to 5.01 mg L−1) compared to the primary nursery phase (3.53 to 3.91 mg L−1). Values for pH oscillated slightly and remained close to the neutrality. The other water parameters presented similar values for both phases of the experiment (Table 1). 3.2. Primary nursery phase Analysis of variance showed no significant difference among the densities for survival rate, average weight, biomass and FCR. Table 1 Pond water parameters (mean ± SD) ) in cage rearing system of M. amazonicum during primary (28 days) and secondary (62 dias) nursery phases. Water parameters
Primary nursery phase
Secondary nursery phase
Minimum temperature (°C) Maximum temperature (°C) Transparency (cm) Dissolved oxygen (mg L−1) pH Conductivity (μs cm−1) Alkalinity (mg CaCO3 L−1) −1 N–NH3 + N–NH+ ) 4 (mg L N–NO2 (μg L−1) −1 N–NO3 (mg L ) P total (μg L−1)
23.1 ± 1.4 26.9 ± 1.3 19.8 ± 3.8 3.72 ± 0.22 7.00 ± 0.14 39.92 ± 1.06 23.19 ± 0.40 1.01 ± 0.09 15.73 ± 1.15 0.23 ± 0.03 47.58 ± 2.28
18.8 ± 2.2 20.7 ± 2.2 28.6 ± 5.3 4.58 ± 0.91 7.04 ± 0.21 39.26 ± 1.40 24.23 ± 1.09 1.19 ± 0.20 15.70 ± 0.83 0.22 ± 0.02 42.00 ± 2.69
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Productivity differed significantly (P b 0.05) and the highest density produced twice as many juveniles compared to the lowest density (Table 2). 3.3. Secondary nursery phase Survival rate was higher than 95% and did not differ significantly among the densities. The values observed were 96.5, 95.6 and 97.5% for the densities of 200, 400 and 800 prawns m−2, respectively. The difference among mean weights for each treatment increased from the first month of growth. At the beginning, it was lower at the density of 800 prawns m−2; but the difference decreased in the last month of the experiment. The adjusted curves plotting the obtained data presented a high coefficient of determination (Fig. 1). Mean weight differed significantly between the densities of 200 and 800 prawns m−2 (P b 0.05), and was inversely proportional to stocking densities. Mean weight values were more homogeneous at densities of 400 and 800 m−2, when compared to the density of 200 m−2, thus resulting in smaller standard deviation values. Density and mean weight displayed a non-linear inverse relationship. On the other hand, biomass and productivity increased linearly with densities (Fig. 2). Biomass also differed significantly (P b 0.01), with the highest value obtained in the highest density treatment (Fig. 2). FCR did not differ significantly among treatments, resulting in values of 4.15, 4.25 and 4.27 for the densities of 200, 400 and 800 prawns m−2, respectively and remained lower than during the primary nursery phase. The productivity of juvenile II was observed to be correlated to stocking densities, and the results were significantly different for all treatments (P b 0.01). For the stocking density of 800 prawns m−2, productivity was four times higher when compared to the lowest density (Fig. 2).
Fig. 1. Mean weights registered in each biometry of M. amazonicum, during the secondary nursery phase.
3.4. Partial budget analysis Juvenile I buying expenses were more than 50% of the total variable cost, and reached up to 69% at the highest density. Labor followed as the second most expensive item, varying between 41 and 26% of the total variable cost depending on the density (Table 3). The lowest density was not cost efficient, therefore the total income did not cover the total variable costs. On the other hand, at the highest density, a net income of US$ 3.42 represented 21.3% of the total variable cost. The results showed that as density increased from 400 to 800 prawns per m2, net income also increased 895%. 4. Discussion The parameters monitored in the present study were similar to the values observed for M. amazonicum in the indoor primary nursery system (Araujo and Valenti, 2005), and in earthen ponds (Keppeler and Valenti, 2006; Moraes-Riodades et al., 2006; Moraes-Valenti and Valenti, 2007; Preto et al., 2008), in which high survival, growth rates and productivity were achieved.
Table 2 Effect of stocking density on survival, mean weight, biomass, FCR and productivity of M. amazonicum in the primary nursery phase (mean ± SD, n = 4). Mean values in the same row followed by different letters are significantly different by Tukey's test. Parameters
Survival (%) Mean weight (g) Biomass (g) FCR Productivity (juveniles I L−1)
Density 4 PL L−1
6 PL L−1
8 PL L−1
83.5 ± 3.9 0.10 ± 0.01 70.0 ± 4.8 0.77 ± 0.05 3.35 ± 0.12a
80.8 ± 6.2 0.09 ± 0.02 88.5 ± 15.0 0.66 ± 0.11 4.82 ± 0.36b
77.1 ± 16.3 0.08 ± 0.01 93.5 ± 15.9 0.71 ± 0.13 6.17 ± 1.33b
Fig. 2. Relationship among stocking densities of M. amazonicum of weight (A), biomass (B) and productivity (C) in the secondary nursery phase (mean ± SD, n = 4). Different letters plotted near the points show significant differences by Tukey's test.
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Table 3 Comparative partial budget analysis among culture densities of M. amazonicum during secondary nursery phase (62 days). Item (unit)
Value US$ unit−1
Density (prawns m−2) 200 Quantity
Yield Juveniles (90 days) revenue Variable costs Juveniles of 30 days old Feed (kg) Labor (h) Packaging (un) Partial VC Interest on partial VC (month) Total VC Net income
0.05 0.028 1.03 2.09 0.03 0.7 %
96 100 0.125 1 1 2
400 −1
Value US$ cage 4.80 2.80 0.13 2.09 0.03 5.05 0.07 5.22 −0.42
The temperatures registered during the period of the study were below the temperature range observed by Moraes-Riodades et al. (2006) and Moraes-Valenti and Valenti (2007). The lower temperature might have had a negative impact on animal growth, mainly during the secondary nursery phase, period in which the temperature fell below 20 °C. On the other hand, the high survival rates showed that the low temperatures were not lethal to the prawns. According to Maciel and Valenti (2009), M. amazonicum tolerates a wide range of variation in the main water physical and chemical characteristics. Nevertheless, it is recommended that M. amazonicum farming be conducted in the warmer months of the year, in order to obtain better growth. Alkalinity was lower than that observed in semi-intensive cultures of M. amazonicum (Keppeler and Valenti, 2006; Moraes-Riodades et al., 2006 and Moraes-Valenti and Valenti, 2007). However, Preto et al. (2008) reported a favorable performance of Amazon prawns during grow-out phase with water alkalinity values very close to the values observed in this research. Values of total ammonia and total phosphorus were slightly high, although within the range appropriate for freshwater prawn culture (Boyd and Zimmermann, 2000). Those high values probably occurred because the fishes stocked in the same pond were fed daily. Since pH values were close to neutral, unionized ammonia (NH3) was not prevalent, which increases in alkaline medium and is considered more toxic for aquatic organisms (Hargreaves, 1998). Penteado et al. (2007) reported survival rates above 90% for the densities of 2, 4 and 8 PL L−1 in an indoor culture of M. amazonicum, as well as productivities that varied from 7 to 8 juveniles L−1 during a 30-day culture. Those results are higher than the values reported in this research, although higher survival rates are expected for indoor cultures, since environmental conditions can be better controlled. Marques et al. (2000) verified that M. rosenbergii postlarvae stocked in cages during 20 days, at densities of 4, 6 and 8 PL L−1, reached average weight (0.051, 0.056 and 0.042 g, respectively) and final biomass (23.3, 24.6 and 30.1 g, respectively), lower than those reported in the present study for M. amazonicum. These data seem to indicate that M. amazonicum better adapts to cage culture at this phase compared to M. rosenbergii. However, the longer storage period of 28 days may have contributed to this result, as well as the lower aggressiveness of M. amazonicum compared to M. rosenbergii, as reported by Araujo and Valenti (2005). The results reported here showed that M. amazonicum can be stocked in cages, during the primary nursery phase, at densities varying from 4 to 8 PL L−1, without compromising their performance. However, at high densities the stress level is higher, causing the prawns to become more sensitive to environmental changes, and increasing mortality. As a consequence, high density requires more care as an adequate feeding management and closer monitoring of
800 Quantity
Value US$ cage−1
9.55
390
19.50
5.60 0.23 3.13 0.03 8.99 0.13 9.12 0.43
400 0.408 2 2
11.20 0.42 4.18 0.06 15.86 0.22 16.08 3.42
Quantity
Value US$ cage
191 200 0.225 1.5 1 2
−1
2
water quality parameters. On the other hand, increasing density doubled the number of juveniles produced, without affecting weight gain, which can represent higher income to the producers. Due to fast growth, the duration of this phase could be shortened, thereby contributing to improve survival rates. During the secondary nursery phase, average weight values were lower than those reported by Kiyohara (2006) for M. amazonicum postlarvae reared in cages and pens (1.1 to 2.0 g) at lower densities (20 to 160 PL m−2). The present trial period (from March to June) may have contributed for this, since water temperature values declined from April on. Kiyohara (2006) also registered survival rates varying from 86.3 to 88.1%, lower than the values found in the present experiment. Lobão et al. (1994) reared M. amazonicum postlarvae in indoor nursery, and reported a survival of 100% after five months of culture at different stocking densities; however, the mean weight of 0.24 g obtained for the highest density (70 PL L−1) was lower than the ones found in the present study. These results seem to show that M. amazonicum grows best in cages installed in natural environments during nursery phases, compared to indoor synthetic tanks. Probably, the presence of natural food associated to the periphyton developed on cage walls and bottom, contributed to improved growth rates. Regarding survival rates, the values reported by Marques et al. (2000) for M. rosenbergii were lower than the ones reported in this study (78.3 to 83.6%); but substrates (polyethylene screens) were added to the cages in this experiment, which might have protected the prawns (Tidwell et al., 2000), consequently improving survival rate and contributing to increase the amount of natural food due to the periphyton developed in the substrates (Uddin et al., 2006). On the basis of these data, it can be assumed that M. amazonicum presents similar growth pattern to M. rosenbergii when cultivated in cages during the secondary nursery phase at high stocking densities, and slower growth rate at lower stocking densities, thus indicating better tolerance to increasing density compared to M. rosenbergii. Another indication of this tolerance is the low standard deviation values verified for weight and biomass at high densities. These results showed that the culture of M. amazonicum in cages at high stocking densities during the secondary nursery phase is feasible. The decrease in mean weight at the highest density (800 prawns m−2) is compensated by an increase in productivity. In addition, homogeneous prawn growth, as observed at the highest density, is desirable because there is no need for grading prawns prior to transferring them to grow-out ponds. The low FCR registered in this phase may be related to the excess of ration supplied (10% of the biomass), although there was no leftover ration on the bottom of the cages. It is possible that the exceeding feed was carried over out of the cages or consumed by the periphyton fauna found on the cage walls and substrates, a process that can happen very fast due to the recycling velocity of the nutrients in this
H.L.A. Marques et al. / Aquaculture 307 (2010) 201–205
environment (Azim et al., 2002). Another hypothesis is the inadequate digestibility of the ration, since it was not specific for M. amazonicum. Similar values of feed conversion (about 3.4) were also reported by Preto (2007) in rearing systems using ration with the same protein content. The lack of studies concerning the nutrition of M. amazonicum did not allow up to now, the development of a ration appropriate for this species. Partial budget analysis indicated the feasibility of using nursery cages to produce M. amazonicum juvenile II, at high densities. However, the producers should consider the higher initial investment in order to use this technology, and that the budget in commercial farms may be different from the budget in experimental culture. In the same way, environmental costs related to the system intensification must also be quantified and considered. On the other hand, the income generated from the prawn sales could be incremented if other market segments were to be explored such as, live baits for sport fishing. As it happens with M. rosenbergii (Marques et al., 2000), the culture of M. amazonicum in nursery cages may optimize the use of natural resources, since the cages may be installed in a variety of bodies of water, including ponds stocked with non-carnivorous fish, in the present study, thus constituting a multi spatial system. Such fish did not cause any damage to the cages and, apparently, their presence did not affect prawn survival rates, weight gain and biomass. In addition to space usage optimization, the culture in cages facilitates prawn harvesting and transferring to grow-out ponds. Also, it makes possible simultaneous rearing of prawns at different growth stages, during the nursery and grow-out phases, thus optimizing the rearing cycle and favoring steady production. The latter becomes very important when culture takes place in sub-tropical countries where climate conditions allow for a maximum of five or six months of production yearly. 5. Conclusions Cage rearing of M. amazonicum during both primary and secondary nursery phases resulted in good prawn survival and growth. The increase of the stocking densities over 4 PL L−1 and 400 juveniles I m−2, respectively resulted in better productivity of juveniles I and II and, in the secondary nursery phase, proportioned favorable net income, given the experimental conditions of the study. Acknowledgments We are thankful to Sao Paulo State Research Support Foundation (FAPESP) for the financial support (Process 2003/07987-3). Also we are thankful to Prof. Wagner Cotroni Valenti, from the Aquaculture Center of Sao Paulo State University (CAUNESP) in Jaboticabal, for supplying the prawn postlarvae used in the experiment. And, finally, we acknowledge the Pindamonhangaba Aquaculture Research Center, for making our work so much easier. References APHA, 2005. Standard Methods for the Examination of Water and Wastewater, American Public Health Association, American Water Works Association, and Water Pollution Control Federation, Washington, DC, 20th ed.
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Aquaculture j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / a q u a - o n l i n e
Stocking densities in cage rearing of Amazon river prawn (Macrobrachium amazonicum) during nursery phases Helcio Luis de Almeida Marques a,⁎, Julio Vicente Lombardi a, Margarete Mallasen b, Helenice Pereira de Barros b, Marcello Villar Boock c a
Centro de Pesquisas em Aquicultura, Instituto de Pesca, Agência Paulista de Tecnologia dos Agronegócios, Secretaria de Agricultura do Estado de São Paulo, Av. Francisco Matarazzo, 455, 05001-900, São Paulo, SP, Brasil Centro APTA do Pescado Continental, Instituto de Pesca, Agência Paulista de Tecnologia dos Agronegócios, Secretaria de Agricultura do Estado de São Paulo, PO Box 1052, 15025-970, São José do Rio Preto, SP, Brasil c Pólo APTA Nordeste Paulista, Agência Paulista de Tecnologia dos Agronegócios, Secretaria de Agricultura do Estado de São Paulo, PO Box 58, 13930-070, Mococa, SP, Brasil b
a r t i c l e
i n f o
Article history: Received 16 April 2010 Received in revised form 24 July 2010 Accepted 28 July 2010 Keywords: Biomass Freshwater prawns Growth Juvenile Productivity Survival
a b s t r a c t Amazon river prawn (Macrobrachium amazonicum) is widely distributed along Brazilian rivers, being one of the native species with a major cultivation potential. This study evaluated stocking densities during primary and secondary nursery phases for M. amazonicum in cages, regarding survival, growth, biomass, food conversion and productivity. The experiment was carried out in 12 cages of 0.5 m2 (iron frames recovered with polyethylene mash) placed inside of a 1500 m2 earthen pond. Early metamorphosed postlarvae (PL) (0.009 ± 0.006 g) were stocked for 28 days (primary nursery phase), at densities of 4, 6, and 8 prawns L−1. In the secondary nursery phase (62 days), densities were 200, 400 and 800 prawns m− 2 (0.12 ± 0.01 g). Prawns were fed commercial pellets (35% crude protein). Water quality parameters were within the adequate range for freshwater prawn culture. In the primary nursery phase, the productivity for density of 8 PL L−1 was two times greater compared to 4 PL L−1 (6.17 and 3.35 juveniles I L−1, respectively) and differed significantly (P b 0.05). In the secondary nursery phase, mean survival was above 95% and did not differ significantly, while mean weight differed (P b 0.05) for the densities of 200 (0.44 g) and 800 (0.36 g) prawns m−2. The highest biomass (143.6 g) was registered at 800 prawns m−2 density and differed significantly (P b 0.01) from lower densities. The productivity of juveniles II also differed significantly among densities, being about four times greater at 800 prawns m−2 compared to lower densities. Net income was positive only at densities greater than 400 prawns m−2, being highest at a density of 800 prawns m−2. Thus, on an experimental basis, the nursery system for M. amazonicum at high densities in cages showed to be viable. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Freshwater prawn culture in Brazil is almost completely restricted to the exotic species, Macrobrachium rosenbergii. There are however, native species of the same genus with culture potential such as M. acanthurus, M. carcinus and Macrobrachium amazonicum (Valenti, 2007). Although there is no evidence of any negative ecological impact of M. rosenbergii, there are benefits to use local species rather than exotic ones for both genetic and environmental reasons (Araujo and Valenti, 2007). Among native species, M. amazonicum has the greater potential for culture due to biological characteristics (Kutty et al., 2000). The biological features of this species are being studied in Brazil since the 1980s, but only recently technological aspects ⁎ Corresponding author. Tel.: +55 11 3871 7535. E-mail addresses: [email protected] (H.L.A. Marques), [email protected] (J.V. Lombardi), [email protected] (M. Mallasen), [email protected] (H.P. de Barros), [email protected] (M.V. Boock). 0044-8486/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2010.07.035
regarding its farming are being developed (Kiyohara, 2006; MoraesValenti and Valenti, 2007; Preto et al., 2008). Freshwater prawn culture is mainly practiced by small farmers. Thus, it is necessary to develop culture technologies that are simple and relatively low cost, in order to make this activity more profitable. Among alternative culture technologies, the use of cages during both primary and secondary nursery phases have been shown to be viable for the culture of the giant river prawn, M. rosenbergii (Marques et al., 2000). According to the same authors, the easy handling and the possibility of using bodies of water of good quality, such as lakes, ponds and even fish farming ponds to install cages, are some of the advantages of using such a system. Kiyohara (2006) studied the use of cages in the nursery phase of M. amazonicum, at stocking densities varying between 20 and 160 prawns m−2, and concluded that productivity can be higher even at higher densities. Therefore, it might be assumed that stocking densities higher than 160 prawns m−2 may be used during primary and secondary nursery phase. The present study aims at evaluating
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2. Material and methods
Prawns were fed as in the primary nursery phase. The experiment lasted for 62 days, at the end of which all the prawns were individually counted and weighed to determine the performance parameters aforementioned.
2.1. Local and experimental structure
2.5. Partial budget analysis
The experiment was carried out in cages installed inside a 1500 m2 earthen pond located at the Pindamonhangaba Aquaculture Research Center, Fisheries Institute, SP, Brazil (22°55′50″S; 45°27′22″W). The same pond was also being used for rearing reproducers of the noncarnivorous fish Prochilodus lineatus (500 g of mean weight), at a density of 1 fish per each 4 m2. A paddle wheel aerator (0.5 HP) was activated nightly from 19:00 to 6:00 h to assure adequate water circulation and prevent stratification. Cages measuring 70 (height) × 100 (length) × 50 cm (width) built with polyethylene mesh (0.7 mm wide) and iron frames, were used as primary and secondary nurseries. Substrates, made of four 40 × 40 cm polyethylene screen pieces, were fixed vertically to the walls inside the cages in order to increase the available space for prawns. The cages were tied to stakes, suspended about 30 cm from the bottom of the pond and about 40 cm immersed in the water. This set up resulted in primary and secondary nurseries of 200 L volume and 0.5 m2 useful area, respectively. Last, the cages were also covered with polyethylene screen to avoid predators and prawn escape.
A partial budget analysis (Shang, 1990) was performed to evaluate the economic feasibility of increasing stocking densities of M. amazonicum during the secondary nursery phase in cages. In this analysis, only the costs and incomes that varied with increasing densities were considered (juveniles, feed, labor and package). The partial budget was based in a 0.5 m2 cage; it was assumed that the cages were stocked with 30 day old-juveniles, costing US$ 0.028 per unity and estimated that the sale price was US$ 0.05 per unity for a 90 day old-juvenile. The interest rate considered was 0.7% per month. The net income was calculated according to the following expression:
the performance of M. amazonicum cultivated at different densities in cages, during primary and secondary nursery phases.
2.2. Water parameters Temperature (a maximum and minimum thermometer Incoterm), dissolved oxygen (Yellow Springs Instruments 550A), pH (Bernauer F-1002) and conductivity (Bernauer F-1000) were measured daily in the morning, at 30 cm depth, in the surrounding cage area. Water transparency was measured early afternoon using a Secchi disk. Samples of water were collected bi-weekly, at the water sub-surface near the cages, to determine alkalinity, total ammonia (N–NH3 + N– NH+ 4 ), nitrite (N–NO2), nitrate (N–NO3) and total phosphorous (total P), All the analyses were carried out according to APHA (2005).
NI = TR−ðVC + IcÞ; in which NI = net income, TR = total revenue from prawn sales, VC = variable costs and Ic = interests on variables costs. 2.6. Statistical analysis Prawn performance data were analyzed by Shapiro–Wilks and Bartlett tests, to assess normality and homocedasticity respectively. As these conditions were satisfied, means were subjected to an analysis of variance (ANOVA) (Zar, 1999). When significant differences were observed among means (P b 0.05), Tukey test was applied. Values expressed as percentages were square root arcsine transformed prior to analysis, while they are presented as non-transformed for easier review. Regressions were performed using all the values obtained in each replicate. 3. Results 3.1. Water parameters
2.3. Primary nursery phase Newly metamorphosed M. amazonicum postlarvae (PL), originated from an experimental laboratory, were stocked in three 1400 L cages similar to the ones described earlier, placed in the same pond, where they were acclimated for a period of 72 h. Afterwards, the PL (0.009 ± 0.006 g) were randomly distributed in 12 primary nurseries, at densities of 4, 6 and 8 PL L−1. A completely randomized design with three treatments (densities) and four replicates (cages) was used. Commercial pellets (35% crude protein), were supplied to prawns twice a day, in the morning and late afternoon, at a daily rate of 10% of the estimated biomass in the cages. After 15 days, the prawns were measured to check growth rate and to adjust the amount of feed to be supplied. Nurseries were harvested 28 days after stocking and the prawns were individually counted and weighed to determine survival rate, mean weight, biomass, food conversion rate (FCR) and productivity (juveniles I L−1). 2.4. Secondary nursery phase Only the largest juveniles from the primary nursery phase were selected and assigned to the secondary nursery, in order to standardize the size of animals and use prawns with a higher growth potential. The juveniles (0.12 ± 0.01 g) were randomly distributed in 12 cages, at the densities of 200, 400 and 800 prawns m−2. A completely randomized design with three treatments (stocking densities) and 4 replicates (cages) was used. The stocking densities were based on the cage net bottom area.
The lowest water temperature value registered during the experiment was 17 °C. Dissolved oxygen presented higher values during the secondary nursery phase (4.11 to 5.01 mg L−1) compared to the primary nursery phase (3.53 to 3.91 mg L−1). Values for pH oscillated slightly and remained close to the neutrality. The other water parameters presented similar values for both phases of the experiment (Table 1). 3.2. Primary nursery phase Analysis of variance showed no significant difference among the densities for survival rate, average weight, biomass and FCR. Table 1 Pond water parameters (mean ± SD) ) in cage rearing system of M. amazonicum during primary (28 days) and secondary (62 dias) nursery phases. Water parameters
Primary nursery phase
Secondary nursery phase
Minimum temperature (°C) Maximum temperature (°C) Transparency (cm) Dissolved oxygen (mg L−1) pH Conductivity (μs cm−1) Alkalinity (mg CaCO3 L−1) −1 N–NH3 + N–NH+ ) 4 (mg L N–NO2 (μg L−1) −1 N–NO3 (mg L ) P total (μg L−1)
23.1 ± 1.4 26.9 ± 1.3 19.8 ± 3.8 3.72 ± 0.22 7.00 ± 0.14 39.92 ± 1.06 23.19 ± 0.40 1.01 ± 0.09 15.73 ± 1.15 0.23 ± 0.03 47.58 ± 2.28
18.8 ± 2.2 20.7 ± 2.2 28.6 ± 5.3 4.58 ± 0.91 7.04 ± 0.21 39.26 ± 1.40 24.23 ± 1.09 1.19 ± 0.20 15.70 ± 0.83 0.22 ± 0.02 42.00 ± 2.69
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Productivity differed significantly (P b 0.05) and the highest density produced twice as many juveniles compared to the lowest density (Table 2). 3.3. Secondary nursery phase Survival rate was higher than 95% and did not differ significantly among the densities. The values observed were 96.5, 95.6 and 97.5% for the densities of 200, 400 and 800 prawns m−2, respectively. The difference among mean weights for each treatment increased from the first month of growth. At the beginning, it was lower at the density of 800 prawns m−2; but the difference decreased in the last month of the experiment. The adjusted curves plotting the obtained data presented a high coefficient of determination (Fig. 1). Mean weight differed significantly between the densities of 200 and 800 prawns m−2 (P b 0.05), and was inversely proportional to stocking densities. Mean weight values were more homogeneous at densities of 400 and 800 m−2, when compared to the density of 200 m−2, thus resulting in smaller standard deviation values. Density and mean weight displayed a non-linear inverse relationship. On the other hand, biomass and productivity increased linearly with densities (Fig. 2). Biomass also differed significantly (P b 0.01), with the highest value obtained in the highest density treatment (Fig. 2). FCR did not differ significantly among treatments, resulting in values of 4.15, 4.25 and 4.27 for the densities of 200, 400 and 800 prawns m−2, respectively and remained lower than during the primary nursery phase. The productivity of juvenile II was observed to be correlated to stocking densities, and the results were significantly different for all treatments (P b 0.01). For the stocking density of 800 prawns m−2, productivity was four times higher when compared to the lowest density (Fig. 2).
Fig. 1. Mean weights registered in each biometry of M. amazonicum, during the secondary nursery phase.
3.4. Partial budget analysis Juvenile I buying expenses were more than 50% of the total variable cost, and reached up to 69% at the highest density. Labor followed as the second most expensive item, varying between 41 and 26% of the total variable cost depending on the density (Table 3). The lowest density was not cost efficient, therefore the total income did not cover the total variable costs. On the other hand, at the highest density, a net income of US$ 3.42 represented 21.3% of the total variable cost. The results showed that as density increased from 400 to 800 prawns per m2, net income also increased 895%. 4. Discussion The parameters monitored in the present study were similar to the values observed for M. amazonicum in the indoor primary nursery system (Araujo and Valenti, 2005), and in earthen ponds (Keppeler and Valenti, 2006; Moraes-Riodades et al., 2006; Moraes-Valenti and Valenti, 2007; Preto et al., 2008), in which high survival, growth rates and productivity were achieved.
Table 2 Effect of stocking density on survival, mean weight, biomass, FCR and productivity of M. amazonicum in the primary nursery phase (mean ± SD, n = 4). Mean values in the same row followed by different letters are significantly different by Tukey's test. Parameters
Survival (%) Mean weight (g) Biomass (g) FCR Productivity (juveniles I L−1)
Density 4 PL L−1
6 PL L−1
8 PL L−1
83.5 ± 3.9 0.10 ± 0.01 70.0 ± 4.8 0.77 ± 0.05 3.35 ± 0.12a
80.8 ± 6.2 0.09 ± 0.02 88.5 ± 15.0 0.66 ± 0.11 4.82 ± 0.36b
77.1 ± 16.3 0.08 ± 0.01 93.5 ± 15.9 0.71 ± 0.13 6.17 ± 1.33b
Fig. 2. Relationship among stocking densities of M. amazonicum of weight (A), biomass (B) and productivity (C) in the secondary nursery phase (mean ± SD, n = 4). Different letters plotted near the points show significant differences by Tukey's test.
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Table 3 Comparative partial budget analysis among culture densities of M. amazonicum during secondary nursery phase (62 days). Item (unit)
Value US$ unit−1
Density (prawns m−2) 200 Quantity
Yield Juveniles (90 days) revenue Variable costs Juveniles of 30 days old Feed (kg) Labor (h) Packaging (un) Partial VC Interest on partial VC (month) Total VC Net income
0.05 0.028 1.03 2.09 0.03 0.7 %
96 100 0.125 1 1 2
400 −1
Value US$ cage 4.80 2.80 0.13 2.09 0.03 5.05 0.07 5.22 −0.42
The temperatures registered during the period of the study were below the temperature range observed by Moraes-Riodades et al. (2006) and Moraes-Valenti and Valenti (2007). The lower temperature might have had a negative impact on animal growth, mainly during the secondary nursery phase, period in which the temperature fell below 20 °C. On the other hand, the high survival rates showed that the low temperatures were not lethal to the prawns. According to Maciel and Valenti (2009), M. amazonicum tolerates a wide range of variation in the main water physical and chemical characteristics. Nevertheless, it is recommended that M. amazonicum farming be conducted in the warmer months of the year, in order to obtain better growth. Alkalinity was lower than that observed in semi-intensive cultures of M. amazonicum (Keppeler and Valenti, 2006; Moraes-Riodades et al., 2006 and Moraes-Valenti and Valenti, 2007). However, Preto et al. (2008) reported a favorable performance of Amazon prawns during grow-out phase with water alkalinity values very close to the values observed in this research. Values of total ammonia and total phosphorus were slightly high, although within the range appropriate for freshwater prawn culture (Boyd and Zimmermann, 2000). Those high values probably occurred because the fishes stocked in the same pond were fed daily. Since pH values were close to neutral, unionized ammonia (NH3) was not prevalent, which increases in alkaline medium and is considered more toxic for aquatic organisms (Hargreaves, 1998). Penteado et al. (2007) reported survival rates above 90% for the densities of 2, 4 and 8 PL L−1 in an indoor culture of M. amazonicum, as well as productivities that varied from 7 to 8 juveniles L−1 during a 30-day culture. Those results are higher than the values reported in this research, although higher survival rates are expected for indoor cultures, since environmental conditions can be better controlled. Marques et al. (2000) verified that M. rosenbergii postlarvae stocked in cages during 20 days, at densities of 4, 6 and 8 PL L−1, reached average weight (0.051, 0.056 and 0.042 g, respectively) and final biomass (23.3, 24.6 and 30.1 g, respectively), lower than those reported in the present study for M. amazonicum. These data seem to indicate that M. amazonicum better adapts to cage culture at this phase compared to M. rosenbergii. However, the longer storage period of 28 days may have contributed to this result, as well as the lower aggressiveness of M. amazonicum compared to M. rosenbergii, as reported by Araujo and Valenti (2005). The results reported here showed that M. amazonicum can be stocked in cages, during the primary nursery phase, at densities varying from 4 to 8 PL L−1, without compromising their performance. However, at high densities the stress level is higher, causing the prawns to become more sensitive to environmental changes, and increasing mortality. As a consequence, high density requires more care as an adequate feeding management and closer monitoring of
800 Quantity
Value US$ cage−1
9.55
390
19.50
5.60 0.23 3.13 0.03 8.99 0.13 9.12 0.43
400 0.408 2 2
11.20 0.42 4.18 0.06 15.86 0.22 16.08 3.42
Quantity
Value US$ cage
191 200 0.225 1.5 1 2
−1
2
water quality parameters. On the other hand, increasing density doubled the number of juveniles produced, without affecting weight gain, which can represent higher income to the producers. Due to fast growth, the duration of this phase could be shortened, thereby contributing to improve survival rates. During the secondary nursery phase, average weight values were lower than those reported by Kiyohara (2006) for M. amazonicum postlarvae reared in cages and pens (1.1 to 2.0 g) at lower densities (20 to 160 PL m−2). The present trial period (from March to June) may have contributed for this, since water temperature values declined from April on. Kiyohara (2006) also registered survival rates varying from 86.3 to 88.1%, lower than the values found in the present experiment. Lobão et al. (1994) reared M. amazonicum postlarvae in indoor nursery, and reported a survival of 100% after five months of culture at different stocking densities; however, the mean weight of 0.24 g obtained for the highest density (70 PL L−1) was lower than the ones found in the present study. These results seem to show that M. amazonicum grows best in cages installed in natural environments during nursery phases, compared to indoor synthetic tanks. Probably, the presence of natural food associated to the periphyton developed on cage walls and bottom, contributed to improved growth rates. Regarding survival rates, the values reported by Marques et al. (2000) for M. rosenbergii were lower than the ones reported in this study (78.3 to 83.6%); but substrates (polyethylene screens) were added to the cages in this experiment, which might have protected the prawns (Tidwell et al., 2000), consequently improving survival rate and contributing to increase the amount of natural food due to the periphyton developed in the substrates (Uddin et al., 2006). On the basis of these data, it can be assumed that M. amazonicum presents similar growth pattern to M. rosenbergii when cultivated in cages during the secondary nursery phase at high stocking densities, and slower growth rate at lower stocking densities, thus indicating better tolerance to increasing density compared to M. rosenbergii. Another indication of this tolerance is the low standard deviation values verified for weight and biomass at high densities. These results showed that the culture of M. amazonicum in cages at high stocking densities during the secondary nursery phase is feasible. The decrease in mean weight at the highest density (800 prawns m−2) is compensated by an increase in productivity. In addition, homogeneous prawn growth, as observed at the highest density, is desirable because there is no need for grading prawns prior to transferring them to grow-out ponds. The low FCR registered in this phase may be related to the excess of ration supplied (10% of the biomass), although there was no leftover ration on the bottom of the cages. It is possible that the exceeding feed was carried over out of the cages or consumed by the periphyton fauna found on the cage walls and substrates, a process that can happen very fast due to the recycling velocity of the nutrients in this
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environment (Azim et al., 2002). Another hypothesis is the inadequate digestibility of the ration, since it was not specific for M. amazonicum. Similar values of feed conversion (about 3.4) were also reported by Preto (2007) in rearing systems using ration with the same protein content. The lack of studies concerning the nutrition of M. amazonicum did not allow up to now, the development of a ration appropriate for this species. Partial budget analysis indicated the feasibility of using nursery cages to produce M. amazonicum juvenile II, at high densities. However, the producers should consider the higher initial investment in order to use this technology, and that the budget in commercial farms may be different from the budget in experimental culture. In the same way, environmental costs related to the system intensification must also be quantified and considered. On the other hand, the income generated from the prawn sales could be incremented if other market segments were to be explored such as, live baits for sport fishing. As it happens with M. rosenbergii (Marques et al., 2000), the culture of M. amazonicum in nursery cages may optimize the use of natural resources, since the cages may be installed in a variety of bodies of water, including ponds stocked with non-carnivorous fish, in the present study, thus constituting a multi spatial system. Such fish did not cause any damage to the cages and, apparently, their presence did not affect prawn survival rates, weight gain and biomass. In addition to space usage optimization, the culture in cages facilitates prawn harvesting and transferring to grow-out ponds. Also, it makes possible simultaneous rearing of prawns at different growth stages, during the nursery and grow-out phases, thus optimizing the rearing cycle and favoring steady production. The latter becomes very important when culture takes place in sub-tropical countries where climate conditions allow for a maximum of five or six months of production yearly. 5. Conclusions Cage rearing of M. amazonicum during both primary and secondary nursery phases resulted in good prawn survival and growth. The increase of the stocking densities over 4 PL L−1 and 400 juveniles I m−2, respectively resulted in better productivity of juveniles I and II and, in the secondary nursery phase, proportioned favorable net income, given the experimental conditions of the study. Acknowledgments We are thankful to Sao Paulo State Research Support Foundation (FAPESP) for the financial support (Process 2003/07987-3). Also we are thankful to Prof. Wagner Cotroni Valenti, from the Aquaculture Center of Sao Paulo State University (CAUNESP) in Jaboticabal, for supplying the prawn postlarvae used in the experiment. And, finally, we acknowledge the Pindamonhangaba Aquaculture Research Center, for making our work so much easier. References APHA, 2005. Standard Methods for the Examination of Water and Wastewater, American Public Health Association, American Water Works Association, and Water Pollution Control Federation, Washington, DC, 20th ed.
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