Stocking density and date decisions in semi‐intensive shrimp Litopenaeus vannamei (Boone, 1931) farming: a bioeconomic approach

This article analyses the optimal selection of stocking density and date in semi‐intensive culture of shrimp Litopenaeus vannamei (Boone, 1931). The empirical evaluation of productive and economic scenarios derived from the specific choice of these management variables is often unfeasible for decision makers. To overcome this limitation, the bioeconomic modelling is widely applicable in aquaculture systems. In the present study, profit maximization for a semi‐intensive shrimp farm is obtained through the development of a bioeconomic model to analyse the combination of stocking density (range: 6–30 postlarvae (PL) m^?2) and date (from March 1st to June 1st) as decision variables for a shrimp farm located in Sinaloa, Mexico. The results show that pond water temperatures prevailing during culture cycle when the stocking date is June 1st (temperature in 19‐weeks culture period: 30.76 ± 0.87°C) and the stocking density is 20–24 PL m^?2 produce a maximized Present Value Profit (PVπ) of  USThis article analyses the optimal selection of stocking density and date in semi‐intensive culture of shrimp Litopenaeus vannamei (Boone, 1931). The empirical evaluation of productive and economic scenarios derived from the specific choice of these management variables is often unfeasible for decision makers. To overcome this limitation, the bioeconomic modelling is widely applicable in aquaculture systems. In the present study, profit maximization for a semi‐intensive shrimp farm is obtained through the development of a bioeconomic model to analyse the combination of stocking density (range: 6–30 postlarvae (PL) m^?2) and date (from March 1st to June 1st) as decision variables for a shrimp farm located in Sinaloa, Mexico. The results show that pond water temperatures prevailing during culture cycle when the stocking date is June 1st (temperature in 19‐weeks culture period: 30.76 ± 0.87°C) and the stocking density is 20–24 PL m^?2 produce a maximized Present Value Profit (PVπ) of  US$^?ha 10 350 and PVπ US$^?ha 2526 for weekly mortality rates at low (2.1%) and medium (5.8%) levels respectively. The marginal change in the cost of feed (±1%) has the greatest effect on PVπ (?0.58% and 0.59% respectively). The discussion focuses on the combined effect of mortality rate, stocking density and especially, on the stocking date decision, for a given production planning framework, taking into account that the stocking date is the main management decision variable to cope with viral diseases outbreaks.     

Development of a zero water discharge (ZWD)—Recirculating aquaculture system (RAS) hybrid system for super intensive white shrimp (Litopenaeus vannamei) culture under low salinity conditions and its industrial trial in commercial shrimp urban farming in Gresik,East Java,Indonesia

This study aims to develop a hybrid zero water discharge (ZWD) - recirculating aquaculture system (RAS) system to improve water quality, as well as the growth, survival, and productivity, of the super-intensive white shrimp culture under low salinity conditions at semi-mass and the industrial level. The study consisted of two parts: (1) a semi-mass trial for the optimization of shrimp production using a hybrid ZWD-RAS system with a total volume of 2.7 m³ at the different shrimp stocking densities of 500 PL/m³, 750 PL/m³, and 1,000 PL/m³ and (2) an industrial trial at a commercial shrimp urban farming facility in Gresik, East Java, with total volume of 110 m³ at the optimum shrimp stocking density from the semi-mass trial. Both the semi-mass and industrial trials were performed in five steps: (1) preparation and installation of the RAS and ZWD system components; (2) preparation of microbial components including nitrifying bacteria, the microalgae Chaetoceros muelleri, and the probiotic heterotrophic bacteria Bacillus megaterium; (3) acclimatization of white shrimp post larvae from the salinity level of 32 ppt to 5 ppt; (4) conditioning of the biofilter used in the RAS and shrimp tank (microbial loop manipulation in ZWD); and (5) shrimp grow-out rearing for 84 days and 60 days for the semi-mass trial and the industrial trial, respectively. The hybrid system combined a ZWD system and an RAS. Shrimp tanks were conditioned with the addition of microbial components for ZWD at the beginning of the culture period. The RAS was operated when NH₄⁺ and NO₂⁻-N levels in shrimp culture reached above 1 ppm until the levels decreased to 0–0.5 ppm. The culture performance in the semi-mass trial at 500 PL/m³, 750 PL/m³, and 1,000 PL/m³ stocking densities was not significantly different for final mean body weight (12.06 ± 5.72, 11.84 ± 3.58, 12.04 ± 3.71 g/ind, respectively) and productivity (4.205 ± 0.071, 4.691 ± 0.025, 4.816 ± 0.129 kg/m³, respectively). Significant differences in survival (70 ± 7%, 53 ± 3%, 40 ± 4%, respectively) and feed conversion ratios (1.54 ± 0.01, 1.82 ± 0.00, 2.16 ± 0.03, respectively) were observed between the three different stocking densities. Water quality parameters and microbial loads during the semi-mass trial were similar for all stocking densities and were within the tolerance levels for white shrimp grow-out production. The results of the semi-mass trial showed that the hybrid ZWD-RAS system can maintain water quality and a microbial load up to a 1,000 PL/m³ stocking density; however, the optimum performance based on survival, feed conversion ratio, and productivity was reached at the 500 PL/m³ stocking density. The industrial trial of the application of the hybrid ZWD-RAS system using the optimal stocking density of 500 PL/m³ resulted in a comparable shrimp survival of 78% with a total production of 298 kg shrimp biomass (equal to a productivity level of 2.7 kg/m³). The overall results of both the semi-mass and industrial trials showed that the application of a hybrid ZWD-RAS system allows optimal shrimp survival and growth at the stocking density of 500 PL/m³ and has high potential for application in commercial shrimp grow-out production at low salinity levels.     

Zootechnical and physiological responses of whiteleg shrimp (Litopenaeus vannamei) postlarvae reared in bioflocs and subjected to stress conditions during nursery phase

The objective of this study was to assess zootechnical and physiological performance of Litopenaeus vannamei postlarvae (PL) reared in three environments (CW, clear water; B, biofloc; BS, biofloc with artificial substrates) at three stocking densities (300, 600, 900 PL/m³) for 8 weeks. At the end of experimentation, shrimp were subjected to hypoxia, and physiological response was again assessed. During rearing, low levels of total ammonia nitrogen, nitrite (NO₂^?) and nitrate (NO₃^?) were observed in B and BS for 600 and 900 PL/m³. For 300 PL/m³, a slight accumulation of NO₂^? and NO₃^? was detected. For the same stocking density, shrimp reared in B and BS showed significantly higher weights than those grown in CW, except for final weight. No significant differences were observed in survival. The use of biofloc and artificial substrates permitted doubling density from 300 to 600 PL/m³ without affecting growth, survival, feed conversion rate and obtaining twice the biomass. Shrimp grown in B and BS stored a surplus of glycogen and carbohydrates in their hepatopancreas, which probably gave them a better physiological capacity to counteract high‐stocking densities and hypoxia. A tendency of a higher adenylate energetic charge was observed in shrimp maintained in B and BS.     

Pond production of Penaeus monodon in relation to stocking density, survival rate and mean weight at harvest in East Java, Indonesia

The relationships between Penaeus monodon production and three crop characteristics in 107 ponds on nine shrimp farms in East Java were studied. Overall differences of production (Mt ha^-1 year^-1), survival rate (%), stocking density (number m^-2) and mean weight at harvest (g) between regions and between farms were significant, while the difference of production between farms was also significant within regions. Overall analysis revealed that production was positively correlated with survival rate, stocking density and mean weight at harvest, while there was a negative correlation between stocking density and survival rate. Results imply that more attention should be paid to improving shrimp survival. The higher on-farm production in South East Java is linked to higher survival rates and higher post-larvae stocking densities than in North West and North East Java, while similar individual weights at harvest to North West East Java are reached. In this context, the relationship between coastal estuarine water quality and yield needs further investigation. Other parameters which need further investigation are farm management, post-larvae origin and duration of the culture period.     

Production and yield of Penaeus semisulcatus (de Haan) cultured at different densities

Two trials were conducted with two sizes, grow‐out (80.0 mg b.w.) and fattening (5.0 g b.w.), of Penaeus semisulcatus to compare the production and yield of shrimp cultured at different stocking densities within an indoor running‐seawater system. In the first experiment, postlarvae were cultured at 50, 100, 150 and 200 m^?3 for 68 days, while in the second experiment, juveniles were cultured at 24, 50, 74 and 100 m^?3 for 126 days. The results of the two experiments showed significant decrease in weight of shrimp as the stocking density increased. During the grow‐out stage, no statistical differences were observed on survival rates among the shrimp stocked at different densities. Thus, as the primary factor to consider at this stage is the number of shrimp produced, it is recommended to use a density of 200 shrimp m^?3. During the fattening stage, the survival rate at the highest density was statistically lower than the other three densities. The mean yield was 437.02, 869.16, 1217.62 and 1446.78 g m^?3 for shrimp stocked at 24, 50, 74 and 100 m^?3 respectively. Although the average harvest size of juveniles at the lowest stocking density was statistically higher than those stocked at the highest stocking density, both sizes (18.12 and 16.67 g) will be classified as one size group in the market, i.e. medium. As the yield significantly increases as the stocking density is increased, it is therefore recommended that the stocking density for the fattening stage be 100 shrimp m^?3.     

River pen culture of giant freshwater prawn Macrobrachium rosenbergii (De Man) in southern Vietnam

A technical and socio‐economic survey conducted in the Dong Thap province of Vietnam to assess the current status of river pen culture of giant freshwater prawn Macrobrachium rosenbergii (De Man) showed that pen culture, which has been developed and operated by farmers' indigenous knowledge, requires more study in order to optimize stocking density and to assess its environmental impacts. In this study, the prawn pens were of rectangular shape, with an average size of 209 m². Prawns were stocked in June at an average density of 62 pieces m^?2 and fed on farm‐made feed and were harvested 2–4 times starting from 4 months after stocking until late December or the following January. The average prawn yield was 0.52 kg m^?2 year^?1, ranging from 0.14 to 1.6 kg m^?2 year^?1. The average net return was US$0.71 m^?2 year^?1, ranging from US$1.24 to 4.37 m^?2 year^?1. About 73% of the farmers achieved positive net returns. The top five constraints for prawn pen culture were lack of knowledge of culture technologies, poor water quality, disease problems, poor quality of wild seed and lack of capital. Almost all farmers have no environmental awareness, and environmental regulations for prawn pen culture have not been established. Field measurements showed that all measured water quality parameters were within the range for good growth of giant freshwater prawns, and indicated that there was no significant accumulation of nutrients and organic matter at the bottoms of rivers or canals.     

Effects of stocking density and feeding duration in cage‐cum‐pond‐integrated system on growth performance,water quality and economic benefits of Labeo victorianus (Boulenger 1901) culture

We evaluated the effect of varying cage stocking density (60, 90 and 120 fish m^?3) and feeding duration (10, 30 and 60 min) in a cage‐cum‐pond‐integrated system on growth performance, water quality and economic benefits in Labeo victorianus culture. Interactions between stocking density and feeding duration significantly (P < 0.05) affected the fish growth performance and yields in the cages‐cum‐pond system. Stocking density of 60 fish m^?3 resulted in the highest growth in cages and in ponds regardless of the feeding duration, but produced lower yields than at stocking density 90 fish m^?3_. The lowest Apparent Food Conversion Ratio (AFCR) in cages occurred at stocking density of 60 fish m^?3 and feeding duration of 30 min. Growth performance in the open ponds declined with increased feeding duration of the caged fish. Survival in cages and in the open ponds decreased with increased cage density, but was not affected by feeding duration. Low dissolved oxygen were recorded, at stocking density of 120 fish m^?3, the lowest DO occurred when feeding of caged fish lasted 60 min. Growth performance, water quality and economic benefits in Labeo victorianus culture positively respond to interaction between stocking density and feeding durations.     

Harvest time optimization considering the stocking density and heterogeneity of sizes in the culture of white shrimp in freshwater

ABSTRACT

The control and management of production factors have been of great economic interest for the aquaculture industry. In this study, the optimal harvesting time that maximizes the net benefits of shrimp cultured in freshwater was determined using a bioeconomic model fitted to six stocking density strategies (90, 130, 180, 230, 280 and 330 shrimp m^?2). A model was constructed which included the size heterogeneity of the culture and the results obtained were compared with the traditional model which assumes size homogeneity for all individuals. The results from both models indicated that the stocking density of 90 shrimp m^?2 was the best management strategy for optimizing net benefits. The economic importance of taking into account size heterogeneity in the culture of the white shrimp in freshwater is discussed.     

Polyculture of western white shrimp,Litopenaeus vannamei Boone, 1931 with Grey mullet,Mugil cephalus Linnaeus, 1758 controls external parasites of western white shrimp

The main aim of this study was to examine the effects of a polyculture system on the control of the external parasites of western white shrimp, Litopenaeus vannamei. To this end, the western white shrimp postlarvae (PLs) were stocked in nine earthen ponds (600 m²) at a density of 20 PLs m^?2 and reared for 4 months. After 40 days of shrimp stocking, Mullets, Mugil cephalus, were stocked at various densities including: control (0 fish/100 m² pond), treatment 1 (T₁: 2 fish/100 m² pond) and treatment 2 (T₂: 4 fish/100 m² pond). Over the course of the experiment, the external parasites of shrimps were investigated by the preparation of a wet mount from the gill tissue. Based on the obtained results, totally two genera of protozoan parasites, i.e. Zoothamnium sp. and Epistylis sp., were identified over the course of the experiment. In all experimental groups, the incidence and abundance of Zoothamnium sp. was significantly higher than Epistylis sp. (P < 0.05). Also, mean incidence per cent and mean abundance of Zoothamnium sp. and Epistylis sp. were significantly lower in the polyculture treatments (T₁ and T₂) compared to the monoculture group (control) (P < 0.05). Throughout this experiment, the total organic matter (TOM %) content of the bottom sediments and biological oxygen demand (BOD₅ mg L^?1) of water samples in the polyculture ponds were significantly lower than the monoculture group (P < 0.05). In contrast, the polyculture ponds had a higher concentration of water dissolved oxygen (O₂ mg L^?1) compared to the monoculture (P < 0.05). In conclusion, our results show that mullet as a secondary farmed species can reduce indirectly the parasitic pollution of western white shrimp probably through reducing the total organic matters in water and sediments and improving the water quality parameters.     

Effect of Shrimp Stocking Density on Size-fractionated Phytoplankton and Ecological Groups of Ciliated Protozoa within Zero-water Exchange Shrimp Culture Systems

Zero‐water exchange shrimp culture systems are being investigated to reduce water and pathogens input and effluent output. The relative abundance and diversity of ciliates have been used as indicators of water quality and ecosystem dynamics in natural systems; however, their occurrence and role in shrimp production systems have not been investigated. The objectives of this research were to describe the succession of the ciliate community in a shrimp grow out system, to investigate the impact of increasing shrimp stocking density on the characteristics of the ciliated protozoa community, and to correlate this with shrimp performance. A growth trial with Litopenaeus vannamei was conducted outdoors with zero‐water exchange and three stocking densities (50, 75 and 100 shrimp/m²). In all treatments, free‐swimming ciliates were dominant in the early weeks, while substrate‐associated ciliates appeared later. The 100 shrimp/m² treatment exhibited a lower abundance of free‐swimming ciliates but higher abundance of hypotrichous ciliates in the second half of production and higher shrimp mortality and lower shrimp growth in the last 2 wk. These results provide a preliminary examination of the role of ciliates in shrimp culture systems and direction for future work in determining the role of protozoa as indicators of water quality.     

Growth and nutrient conversion of white shrimp Litopenaeus vannamei (Boone) and Nile tilapia Oreochromis niloticus L. in an integrated closed recirculating system

We investigated the effects of the stocking density of white shrimp (Litopenaeus vannamei) on shrimp and tilapia growth and nutrient conversion in an integrated closed recirculating system both with and without Nile tilapia (Oreochromis niloticus). A 2 × 3 factorial design involving tilapia presence/absence and shrimp stocking densities of 40, 80 and 120 m^?2 was applied, using a tilapia:shrimp ratio of 0.025. There were no significant interactions between tilapia presence and shrimp stocking density in terms of shrimp growth performance or feed utilization. The presence of tilapia had no effect on the shrimp growth rate, survival rate or total weight gain (%). Shrimp growth declined significantly with increased shrimp stocking density, but the growth of tilapia was not significantly different among the three shrimp densities tested. The conversion of feed nitrogen and phosphorus into total harvested animal biomass was significantly higher in the presence than in the absence of tilapia. The nutrient conversion rate at the lowest shrimp density (40 m^?2) was significantly higher than at the highest density tested (120 m^?2).     

The effects of sediment redox potential and stocking density on Pacific white shrimp Litopenaeus vannamei production performance and white spot syndrome virus resistance

Redox potential represents the intensity of anaerobic condition in the pond sediment, which may affect the dominant microbial transformations of substances, the toxins production, mineral solubility, as well as the water quality in the sediment–water interface inhabited by the shrimp. This study evaluates the effect of sediment redox potential in conjunction with stocking density on shrimp production performance, immune response and resistance against white spot syndrome virus (WSSV) infection. A completely randomized two factors experimental design was applied with three different sediment redox potential, i.e. ?65, ?108 and ?06 mV, and two shrimp densities, i.e. low (60 shrimp m^?2) and high (120 shrimp m^?2). Shrimp juveniles with an initial mean body weight of 5.32 ± 0.22 g were maintained in semi‐outdoor fibre tanks (270 L in capacity) for 35 days of experimental periods. At the bottom of each tank, 5‐cm deep soil substrate with different redox potential was added according to the treatments. The survival and biomass production were significantly reduced at ?206 mV sediment redox potential, regardless of stocking density. Highly negative sediment redox potential (?206 mV) and higher stocking density significantly reduced total haemocyte counts and phenoloxydase activity, and shrimp resistance to WSSV infection. We recommend to maintain the redox potential of pond sediment at a level of more than ?206 mV.     

Stocking strategies for production of Litopenaeus vannamei (Boone) in amended freshwater in inland ponds

The performance of the Pacific white shrimp Litopenaeus vannamei (Boone) under various stocking strategies was evaluated in earthen ponds filled with freshwater amended with major ions. Six 0.1‐ha earthen ponds located in Pine Bluff, AR, USA, were filled with freshwater in 2003 and 2004, and potassium magnesium sulphate added to provide 50 mg K⁺ L^?1 and stock salt added to provide 0.5 g L^?1 salinity. In 2003, three ponds either were stocked with PL₁₅ shrimp (39 PL m^?2) for 125 days of grow out or with PL₂₅ shrimp for 55 days (23 PL m^?2) followed by a 65‐day (28 PL m^?2) grow‐out period. In 2004, ponds were stocked with 7, 13 or 30 PL₁₅ m^?2 for 134 days of grow out. Salinity averaged 0.7 g L^?1 during both years, and concentration of SO₄^?2, K⁺, Ca²⁺ and Mg²⁺ was higher, and Na⁺ and Cl^? was lower in amended pond water than in seawater at 0.7 g L^?1 salinity. Potassium concentration in amended water was 52–61% of the target concentration. Shrimp yields ranged from 3449 kg ha^?1 in 2003 to 4966 kg ha^?1 in 2004 in ponds stocked with 30–39 PL₁₅ m^?2 for a 125–134‐day culture period. At harvest, mean individual weight ranged from 17.1 to 19.3 g shrimp^?1. In ponds stocked with PL₂₅ shrimp, yields averaged 988 and 2462 kg ha^?1 for the 1st and 2nd grow‐out periods respectively. Gross shrimp yield in 2004 increased linearly from 1379–4966 kg ha^?1 with increased stocking rate. These experiments demonstrated that L. vannamei can be grown successfully in freshwater supplemented with major ions to a final salinity of 0.7 g L^?1.     

An evaluation of intraspecific competition for Pacific white shrimp Penaeus vannamei (Boone) in extensive/semi-intensive ponds

The hypothesis that intraspecific competition affects survival and growth during the culture and harvest at extensive/semi-intensive Penaeus vannamei shrimp ponds was evaluated. Thus, the effect of stocking density on the biomass, shrimp average weight, survival, and economic performance during the culture (133 days) and at the harvest of the P. vannamei shrimp was investigated in 400 m² earthen ponds. In order to reduce the likelihood of infectious diseases, shrimp received preventive health treatments (probiotics and β-1,3/1,6-glucans) during all culture phases. In this way, the effect of density on the intraspecific competition for space/food was isolated. Ponds stocked at 6, 9, and 12 shrimp m^?2 showed competition-dependent growth. Ponds stocked at 12 shrimp m^?2 presented a mortality (12 %) between days 76 and 99. Competition, and accordingly individual growth reduction, could have begun at day 76 at a density of 5 shrimp m^?2. Survival was significantly higher at 6 shrimp m^?2 (84.2 ± 6.2 %) compared with the 12 shrimp m^?2 (64.8 ± 12.4 %) treatment, while no significant differences in yield were observed between both treatments. Ponds stocked at 3 and 6 shrimp m^?2 presented the best benefit–cost rates. The optimal shrimp density during the experimental culture was 5 shrimp m^?2. Given the experimental conditions and considering the fraction of density-independent mortality observed, the optimum stocking density was found to be 6 shrimp m^?2.     

Growout production of camouflage grouper, Epinephelus polyphekadion (Bleeker), in a tank culture system

Growout production of the camouflage grouper, Epinephelus polyphekadion (Bleeker), in a 10-m³-capacity fibreglass tank culture system was evaluated, using hatchery-produced fingerlings (56-59 g initial weight) at stocking densities of five, 15 and 45 fish m^?3. During the first 9 months of a 12-month growout period, the fish were fed twice a day with a moist pellet feed containing 40.9% protein. From month 10 onwards until harvest, the fish were fed moist pellets in the morning and trash fish in the evening at a 1:1 ratio. The final weight of fish at harvest was up to 900 g, with mean weights of 544.6 ± 170.72 g at five fish m^?3, 540.2 ± 150.82 g at 15 fish m-^?3 and 513.3 ± 134.52 g at 45 fish m^?3. The results showed no significant differences (P > 0.05) in growth rate and fish size between the different stocking densities tested. The average daily growth rate ranged from 0.62 to 3.38 g fish^?1 day^?1, with mean weights of 1.49 ± 0.74 g fish^?1 day^?1 at five fish m^?3 through 0.53 to 2.38 g fish^?1 day^?1, 1.32 ± 0.57 g fish^?1 day^?1 at 15 fish m^?3 to 0.48-3.32 g fish^?1 day^?1 and 1.31 g fish^?1 day^?1 at 45 fish m^?3 stocking density. Although up to 100% survival was observed at the lowest stocking density, the survival rate significantly decreased (P < 0.05) with increasing stocking density. The food conversion ratio (FCR) significantly decreased (P <0.05) with increasing stocking densities, showing efficient feed utilization with increasing stocking densities of E. polyphekadion. The FCR averaged 2.1 at a stocking density of 45 fish m^?3. The yield in terms of kg fish produced m^?3 of water used in the culture system significantly increased (P < 0.001) from five to 45 fish m^?3. The yield averaged 17.3 ±0.53 kg m^?3 at a stocking density of 45 fish m^?3. The present results show that the present tank culture system could sustain more biomass in terms of increasing fish stocking densities. The growth performance of E. polyphekadion observed during this investigation has been reviewed with other grouper species.     

Some Limiting Factors in Superintensive Production of Juvenile Pacific White Shrimp,Litopenaeus vannamei,in No‐water‐exchange,Biofloc‐dominated Systems

Superintensive shrimp culture in zero‐exchange, biofloc‐dominated production systems is more biosecure and sustainable than traditional shrimp farming practices. However, successful application of this technology depends upon optimizing dietary formulations, controlling Vibrio outbreaks, and managing accumulative changes in water quality and composition. A 49‐d study investigated the effect of two commercial feeds of differing protein content and an indoor limited‐exchange, biofloc‐dominated culture environment on Litopenaeus vannamei performance and tissue composition, water quality and ionic composition, and Vibrio dynamics. Juveniles (5.3 g) were stocked at 457/m³ into four 40 m³ shallow raceways containing biofloc‐dominated water and fed one of two commercial feeds with differing protein content, 35 or 40%. Shrimp performance, Vibrio populations, and changes in shrimp and culture water composition were monitored. There were no significant differences (P > 0.05) in shrimp performance (survival, weight, growth, specific growth rate, total biomass, yield, feed conversion ratio, and protein efficiency ratio) or proximate composition between feed types. The 40% protein feed resulted in higher culture water nitrate and phosphate concentrations, alkalinity consumption and bicarbonate use, and higher phytoplankton density. The presence of Vibrio, specifically Vibrio parahaemolyticus, reduced shrimp survival. This survival decrease corresponded with increased culture water Vibrio concentrations. Culture water K⁺ and Mg²⁺ increased significantly (P < 0.05), and Sr²⁺, Br^?, and Cl^? decreased significantly (P < 0.05) over time. While Cu²⁺ and Zn²⁺ did increase in shrimp tissue, no heavy metals accumulated to problematic levels in culture water or shrimp tissue. These results demonstrate the importance of monitoring Vibrio populations and ionic composition in limited‐exchange shrimp culture systems.     

Enhancing water use efficiency in monoculture of Litopenaeus vannamei: Impacts on pond water quality,waste production,water footprint and production performance

We studied the effect of rearing densities of Pacific white shrimp, Litopenaeus vannamei in three densities with three replicate treatments [T₁: 0.4 million post-larvae (PL) ha⁻¹, T₂: 0.5 million PL ha⁻¹, T₃: 0.6 million PL ha⁻¹] and water cutback approach on rearing environment, water use efficiency, water footprint and production performance. Conditional water exchange was carried out based on water quality parameters. Water quality suitability index was very good (7.5–9.0) up to 13th, 10th and 5th week of culture in T₁, T₂ and T₃, respectively; which was attributed to rearing density, smaller-sized shrimp and low early feed input. Optimum rearing density of 50 PL m^-2 (T₂) led to total water use of 3.25 × 10⁴ m³. It was seeming as a way to improve shrimp productivity (10.58 t ha⁻¹ 120 d⁻¹), consumptive water use index (1.72 m³ kg^-1 biomass), total water footprint (1229 m³ t⁻¹ biomass) and net consumptive water productivity (USD 1.28 m^-3). L. vannamei culture with low to moderate water exchange as in T₂, helped uphold water quality suitable for the shrimp growth, improved water use efficiency (0.58 kg biomass m^-3 water), minimized sediment load (45.3 m³ t^-1 biomass), effluent outputs (0.63 × 10⁴ m³), pumping cost (USD 30.1 t⁻¹ biomass produced), and ratio of output value to the cost of cultivation (1.97). The findings and advancement in knowledge would offer the basis to augment shrimp rearing efforts and the water management approaches will help in preventing the production of waste and effluent while increasing water use efficiency and production performance.     

Bioeconomic analysis of intensive production of the blue shrimp Litopenaeus stylirostris (Stimpson)

A bioeconomic approach was used to evaluate random variation of growth and mortality parameters and feed conversion ratio (FCR) for intensive production of the blue shrimp Litopenaeus stylirostris (Stimpson). Severe mortality problems caused by high impact diseases were not considered in this analysis. For a 50‐ha farm, the maximum values of the internal rate of return (IRR=44%) and net revenue above operation costs (NR=US$1 211 000) were obtained for a stocking density of 67 postlarvae (PL) m^?2 during winter–spring (cycle 1) and 65 PL m^?2 during summer–autumn (cycle 2). Regardless of the density used for cycle 1, stocking at 50 and 65 PL m^–2 for cycle 2 sufficed to obtain, respectively, IRRs greater than the minimum attractive IRRs of 15% and 30%. A frequency distribution of IRR, projected for densities of 67 and 65 PL m^?2, showed high confidence in obtaining IRR values above 15% and 30% (i.e. confidence >99% and 92% respectively). The frequency distribution of NR showed that the farm could operate without economic losses. Stocking a minimum of 53% of the capacity of the farm would guarantee positive NR. Sensitivity analysis indicated that the IRR and NR were mainly influenced by mortality rate, selling price, density, final weight and FCR.     

The effectiveness of a commercial microbial product in poorly prepared tiger shrimp, Penaeus monodon (Fabricius), ponds

The efficacy of a commercial microbial product was tested in commercial tiger shrimp, Penaeus monodon (Fabricius), ponds for one culture period in Kuala Selangor, Malaysia. Four ponds with replicates for treatment and control were used. The pond bottom was dried but the organic sludge was not removed as normally practised in pond preparation. The ponds were stocked with 15 post‐larvae at the rate of 31.m^?2. Physical, chemical and biological parameters of the pond were analysed every 2 weeks during the culture period. Water quality parameters remained within the optimum range for shrimp culture except for ammonia‐nitrogen being significantly higher in control ponds and silica in treated ponds. Benthic organisms were not found in any of the ponds. The average counts of different bacteria were not significantly higher in treated ponds than control. Because of poor health, the shrimp were harvested earlier (72 days) than the usual 120 days. An average of 875.60 ± 67.00 kg shrimp ha^?1 was obtained in treated ponds with a feed conversion ratio (FCR) of 1.57 ± 0.10 and survival rate of 42.35 ± 5.37% compared with 719.50 ± 130.94 kg shrimp ha^?1, 2.99 ± 0.70 and 21.25 ± 3.26%, respectively, in control ponds. Neither the microbial product nor the frequent water exchange was effective in overcoming the problems caused by the poor pond bottom.