The effects of density and artificial substrate on intensive shrimp Litopenaeus vannamei nursery production

Recirculating aquaculture systems (RAS) can be installed indoors, allowing year-round production of tropical animals in nearly any climate. A nursery phase is commonly used in Litopenaeus vannamei production since it allows for enhanced biosecurity and better quantification of animals while reducing space requirements. However, it is unclear whether animal density and inclusion of artificial substrate may improve shrimp performance during the nursery phase. In this experiment, we compared shrimp production parameters in two stocking densities with or without the use of an artificial substrate by creating four treatments: low-density LD; 1500 PL/m⁻³, low-density with substrate LDS, high-density HD; 3000 PL/m⁻³), and high-density with substrate (HDS). The LDS and HDS treatments included 0.46-m² of high-density polyethylene 2.5-cm mesh as a substrate, which increased the tank surface area by 21 %. Each treatment was randomly assigned to four 160-l culture tanks, each with a biofilter. The shrimp had an initial weight of 4 mg and were grown for 50 days. The low-density treatments had significantly higher dissolved oxygen (DO) and pH than the high-density treatments (P ≤ 0.001). Specifically, LDS had the highest DO and pH followed by the LD, HD, and HDS treatments, respectively. High-density treatments had significantly higher NO₂-N levels than low-density treatments during week 2 of the experiment when an unusually high concentration of nitrite was observed. FCR was significantly lower in both low-density treatments than in high-density treatments. At harvest, the total biomass (kg m⁻³) was significantly higher in high-density treatments than in low-density treatments (P ≤ 0.001), and the HDS treatment had a significantly greater biomass output than HD. Producers should consider artificial substrate and higher densities during nursery production to maximize shrimp production; however, the effects on water quality should also be taken into account.     

Water quality,production parameters and nutritional condition of Litopenaeus vannamei (Boone, 1931) grown intensively in zero water exchange mesocosms with artificial substrates

The effect of artificial substrates on the water quality, production parameters and nutritional condition was assessed in experimental intensive cultures of Litopenaeus vannamei grown in mesocosm units with zero water exchange. The initial stocking densities in triplicate 1000 L tanks were 600 and 800 g of juvenile shrimp (2.7 g) per unit, with (W) and without (WO) artificial substrates. There were no significant differences between the water quality parameters of the four treatments. In the tanks with the lower stocking biomass, the best survival (96.7% vs. 87.0%), growth rate (1.69 vs. 1.35 g week⁻¹), final biomass (1969.6 vs. 1516.0 g m³) and feed conversion ratio (1.30 vs. 1.90) were obtained with artificial substrates. Similar results were observed for the higher stocking biomass (90.9% vs. 74.5%, 1.50 vs. 1.13 g week⁻¹, 2221.6 vs. 1560.8 g m³, and 1.50 vs. 2.60 respectively). The nutritional condition of shrimp was improved using artificial substrates. The protein content in muscle was higher (21.6% and 20.4%) in ponds with substrates as compared with the control (21.2% and 15.9%).     

Format and mode of artificial substrate fixation affect the performance of Litopenaeus vannamei in high‐density rearing systems

We investigated whether the positive impacts of artificial substrates on shrimp performance are altered in any way by their format or mode of fixation in the tanks. To examine this question, substrates were fixed vertically in the water column in three different configurations: SCF treatment (Substrate Completely Fixed), SPF treatment (Substrate Partially Fixed) and SFF (Substrate in Frond Format). Another treatment received no substrate and served as control (WS = Without Substrate). The shrimp were cultured for 38 days in intensive biofloc culture tanks at a stocking density of 1,125 shrimp m^?3. In general, water quality variables were similar among treatments and remained within the appropriate range for shrimp culture. The final biomass was higher (8.5 kg m^?3) and the feed conversion ratio (FCR) lower (1.6) in all tanks with substrates when compared with the WS treatment tanks (final biomass = 6.3 kg m^?3 and FCR = 3.1). However, only shrimp from the SCF and SPF treatments had a higher survival rate (>95.0%) compared to those in WS tanks (75.9%), which was statistically similar to the SFF treatment (88.0%). These results show that substrate format and its mode of fixation in tanks can alter shrimp performance. In well‐aerated intensive tanks, substrates in frond format are constantly pushed to the tank surface, making it difficult for shrimp to adhere to the screens. In such situation, the extra surface provided by the substrates is not always available to the shrimp, a fact that minimizes the positive effects of substrate.     

The quantity of artificial substrates influences the nitrogen cycle in the biofloc culture system of Litopenaeus vannamei

This study evaluated the influence of different quantities of artificial substrate on water quality and the performance of Litopenaeus vannamei in an integrated biofilm-biofloc culture system. Thus, three treatments were performed: the control, the treatment without the addition of artificial substrate; T200, the treatment with a 200 % increase in the lateral area of the tanks using artificial substrates; and T400, the treatment with a 400 % increase in the lateral area of the tanks using artificial substrates. The study was conducted in nine 800 L tanks over 60 days. The animals were stocked at an initial density of 300 shrimp.m⁻² (equivalent to 500 shrimp m^-3), with an initial weight of 1.27 g (± 0.48). Ammonia concentrations did not differ significantly between treatments (p > 0.05). Increasing the amount of substrate from 200 % to 400 % did not cause significant differences in the nitrite concentrations between these treatments. However, in the control treatment, nitrite remained high (above 20 mg.L^-1) for a long period, negatively affecting shrimp performance. Nitrate was lower in T400, indicating a more dynamic process in the nitrogen cycle when the quantity of artificial substrate increased. Weekly growth rates, final weight, survival, and productivity were higher in the treatments integrating biofilm and biofloc substrates and did not show significant differences between T200 and T400. The results demonstrate the importance of artificial substrates in enhancing the water quality in biofloc culture systems over the long term, mostly in terms of maintaining nitrite concentrations below levels toxic to L. vannamei. The performance of the shrimp and the improved water quality at the end of the study reflected the advantages provided by incorporating artificial substrates in shrimp biofloc culture.     

Biofilm versus biofloc: Are artificial substrates for biofilm production necessary in the BFT system?

The aim of this study was to evaluate the addition of artificial substrates in biofloc technology systems that are used for the intensive production of Litopenaeus vannamei. The experiment lasted 35 days. Tanks each with a useful volume of 800 L were filled with water containing bioflocs (25 % of the total volume) and filtered seawater. Three treatments with three replicates each were compared: (1) Ctrl (control), i.e., without the addition of artificial substrate, (2) 200 and (3) 400, with added artificial substrate equivalent to 200 and 400 % of the lateral area of the tanks, respectively. The shrimp with initial weight of 0.40 ± 0.15 g were stocked at a density of 300 shrimp/m². Feed (Guabi/38 Active, Brazil) was supplied two times per day. The water quality parameters were suitable for the production of L. vannamei. The settleable solids (SS) were higher in the Ctrl treatment (82.1 ± 19 mL L^?1) and differed statistically from the 200 and 400 treatments that presented average SS values below 10 mL L^?1. The reuse of water with bioflocs accelerated nitrification in the tanks, and no significant differences were shown between tanks. The presence of biofilm did not interfere with ammonium or nitrite levels, but it did serve as a food source that optimized shrimp performance, as shown by higher final weights. More studies are needed to evaluate the circulation and mixing intensity effects of the substrates on water throughout the production cycle.     

Intensive production of juvenile tiger shrimp Penaeus monodon: An evaluation of stocking density and artificial substrates

Tiger shrimp Penaeus monodon were intensively grown from PL₁₅ for 56 d in tank systems at stocking densities of 1000 and 2000 shrimp m^− 3, with and without the addition of artificial substrates (AquaMat® (buoyant and non-buoyant) and polyethylene mesh) at each density. Shrimp growth was significantly greater at the lower density and when substrates were added. Mean shrimp weight at harvest ranged from 0.64 ± 0.06 g (2000 shrimp m^− 3, no added substrate) to 1.17 ± 0.01 g (1000 shrimp m^− 3, added substrate). Survival was high and averaged 79.5 ± 2.7% across all treatments. The addition of substrates significantly increased survival at both stocking densities; however, survival was not significantly affected by stocking density. A maximum harvest density of 1645 shrimp m^− 3 and biomass of 1.27 kg m^− 3 were produced at a stocking density of 2000 m^− 3 with added substrates. Both harvest density and biomass significantly increased with stocking density and addition of substrates. The feed conversion ratio (FCR) of formulated feed was significantly lower when substrates were added. The results show that growth of P. monodon juveniles was inversely related to stocking density during intensive production. However, production output was significantly increased by addition of artificial substrates, which enhanced both growth and survival.     

Effects of Artificial Substrate and Stocking Density on the Nursery Production of Pacific White Shrimp Litopenaeus vannamei

Nursery production may be enhanced by the addition of artificial substrate to increase the surface area upon which shrimp graze and to serve as refuge. The objective of this study was to assess the effects of the artificial substrate, AquaMats^TM, on the performance of postlarval Pacific white shrimp Litopenaeus vannamei stocked at three densities. Eighteen 230-L tanks were stocked with 10-d postlarvae (mean weight < 0.01 g). Six treatments were evaluated and consisted of shrimp stocked at three densities (778 shrimp/m², 1,167 shrimp/ m², and 1,556 shrimp/m²) with and without access to artificial substrate. Shrimp in all treatments received a commercial diet ad libitum . After 6 wk, shrimp were harvested from each nursery tank, counted, and batch weighed. Mean final weight, survival, production, feed conversion ratio, and water quality parameters were analyzed by 2-way ANOVA. There were highly significant ( P < 0.001) density and substrate effects on final weight, but there was no significant interaction effect. Final weight was 26.0, 17.4, and 34.5% greater in treatments with substrate than without substrate when stocked at 778, 1,167, and 1,556 shrimp/m², respectively. There was no significant density, substrate, or interaction effect on survival or water quality. Mean survival was ± 89.1% for all treatments. Increased shrimp growth in the presence of added substrate was likely due to the availability of attached particulate organic matter on the AquaMats^TM that served as an additional food source. Results from this study indicate that artificial substrate can be used to mitigate the potential negative effects of high stocking density on growth of L. vannamei in nursery systems.     

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.     

Prenursery of the Pacific white shrimp in a biofloc system using different artificial substrates

This study evaluated different artificial substrates during pre-nursery of Pacific white shrimp in a biofloc system. Post-larvae (PL 5–80 PL L⁻¹) were raised in 60 L tanks filled with 52 L of chlorinated seawater (35‰) and 6 L of the microalga Chaetoceros muelleri. Four treatments were performed, including control (no artificial substrate), Bidim^® (geotextile), mosquito net screen (2 mm mesh) and Needlona^® (polyester fiber). The total surface area of artificial substrate comprised 100% of the tank area (0.89 m²). PLs were fed nine times a day using commercial feed. Molasses was added in all treatments four times a day at an average carbon:nitrogen ratio of 14.7:1. The experiment was carried out until the PLs reached PL20, and during this time, water quality, survival, weight gain and survival to salinity stress were all evaluated. Water quality parameters remained within the accepted levels for shrimp rearing, with the exception of total suspended solids (TSS) in mosquito net screen and control, which had the highest values (507 ± 5.50 mg L⁻¹ and 565 ± 23.46 mg L⁻¹, respectively). Using Needlona^® as artificial substrate increased the survival rate (91 ± 11.6%) and reduced TSS (42%) when compared to the control. No significant differences were observed in final weight and survival to salinity stress. Among the different substrates, Needlona^® was the most suitable for application in Pacific white shrimp prenursery in the biofloc system, essentially because it could maintain levels of solids suspended in water without the use of clarifiers or water exchange, resulting in higher survival.     

Growth and performance of the whiteleg shrimp Penaeus vannamei (Boone) cultured in low‐salinity water with different stocking densities and acclimation times

We evaluated the performance of whiteleg shrimp Penaeus vannamei (Boone, 1931) in response to different stocking densities and acclimation periods. Shrimp postlarvae were acclimated from seawater (30 g L^?1) to low‐salinity well water (<1.0 g L^?1) at a constant hourly reduction rate of 40, 60, 80 and 100 h. After acclimation to low‐salinity well water, postlarvae from each acclimation time treatment were stocked in three replicate tanks at densities of 50, 100, 150 or 200 shrimps m^?2 for 12 weeks of growth. Salinity averaged <1.0 g L^?1 for each growth study. The different treatments resulted in significant differences in both the final body weight and the survival rate (SR). Shrimp acclimated for 100 h showed substantially improved survival (83%) relative to shrimp acclimated for shorter periods. Shrimp yields for all cultured periods ranged from 0.32 kg m^?2 in tanks stocked at 50 m^?2 to 1.14 kg m^?2 in tanks stocked at 200 m^?2. We conclude that whiteleg shrimp can be successfully grown in low‐salinity well water, and that the growth, production output and SRs are significantly higher when shrimp are acclimated for longer periods.     

Strategies for ammonium and nitrite control in Litopenaeus vannamei nursery systems with bioflocs

In biofloc technology (BFT) rearing systems, nitrogen compounds, specially ammonia and nitrite, have to be controlled by microbial pathways, mainly through the activity of heterotrophic and chemoautotrophic bacteria. The objective of this work was to assess different water preparation strategies (heterotrophic, chemoautotrophic and mature) in BFT system for nursery of Pacific white shrimp (Litopenaeus vannamei). A 35-day study was conducted with post-larvae shrimp (0.08 g) stocked in twelve 300 L tanks at a stocking density of 2000 shrimp m⁻³. The water preparation strategies for shrimp rearing that were evaluated in this study included: i) Heterotrophic treatment, where the water received sugar as a carbon source; ii) Chemoautotroph treatment, where ammonium and nitrite salts were added to the water; and iii) Mature treatment, which was created by the addition of a significant amount of water containing mature biofloc from another established BFT system. In both mature and chemoautotrophic treatments, the nitrification process was able to keep toxic nitrogen compounds (ammonia and nitrite) at low levels without the addition of carbohydrates. In contrast, heterotrophic system showed peaks of ammonia and nitrite during the rearing cycle, and the level of these compounds were found to be higher in this treatment (relative to the mature and chemoautotrophic treatments). The chemoautotrophic system exhibited a lower abundance of bacteria from the family Vibrionaceae in the beginning of the experiment compared to the heterotrophic and mature treatments. The combination of low Vibrionaceae abundance and good water quality resulted in improved growth performance in this treatment. These findings demonstrate the importance of manipulating the environment of BFT systems to induce an enrichment of nitrifying bacteria before stocking shrimp. We have also found that the addition of a carbon source to BFT systems is necessary only in emergency situations, when ammonia spikes need to be controlled.     

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.     

Effects of Haematococcus pluvialis on the water quality and performance of Litopenaeus vannamei using artificial substrates and water exchange systems

Two kinds of culture systems were constructed, namely, an artificial substrate system (novel sponge biocarrier, SB) and a water exchange system (WE), to evaluate the effects of the microalga Haematococcus pluvialis on the water quality and performance of whiteleg shrimp (Litopenaeus vannamei). The results showed that the average NH₄⁺-N concentration with H. pluvialis was lower than those without it. The average concentration of NO₂^?-N and NO₃^?-N in SB system were significantly decreased than those present in WE system, but there was no significant difference in SB system. The growth performance of shrimp with H. pluvialis was superior to that without it. The final average weight and growth rate of shrimp in SB1 and WE1 tanks were differed significantly among that present in SB2 and WE2 tanks (p?<?0.05). SB1 tended to have the highest average weight gain and lowest feed conversion ratio. The shrimp survival was significantly higher in SB1 and WE1 tanks (89.06% and 82.29%, respectively) than that present in SB2 and WE2 tanks (78.13% and 48.44%, p?<?0.05). The high-throughput sequencing results showed that the diversity of bacterial communities and the abundance of bacteria related to the nitrogen cycle and the degradation of organic matter were increased. The present study showed that H. pluvialis had positive effects on shrimp culture in using artificial substrate system and water exchange system.

     

Determining the effects of stocking density and temperature on growth and food consumption in the pharaoh cuttlefish, <Emphasis Type="Italic">Sepia pharaonis</Emphasis>, Ehrenberg 1890

The purpose of this experiment was to observe the impact of stocking density on growth and food consumption of juvenile Sepia pharaonis reared at 23 and 28°C. Two groups of 32 cuttlefish each were reared in closed recirculating seawater systems with water temperatures of 23°C (group A) and 28°C (group B). Each group was divided into three treatments with two replicates per treatment: low-density (equivalent to 20 cuttlefish m⁻²), medium-density (equivalent to 100 cuttlefish m⁻²), and high-density (equivalent to 200 cuttlefish m⁻²). Measured amounts of live food were added three times a day and the wet body weight of each cuttlefish was measured once a week during the 42-day study. Cuttlefish in group B had higher growth rates and food consumption than cuttlefish in group A. The different stocking densities in group B affected the size of the cuttlefish whereas the stocking densities of the cuttlefish in group A treatments did not lead to different sizes between densities. Overall, the gross growth efficiency of the high-density treatments was lower than that of the low-density treatments, as was the weight of the cuttlefish in the high-density treatment. Although the wet weights of group A treatments were not significantly different (P > 0.05), the wet weights of the cuttlefish in the high-density, group B, treatment were lower than those in the low and medium density treatments. This decrease in individual size suggests that stocking densities of 100 to 200 cuttlefish m⁻² may interfere with growth.     

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.     

Effects of Potassium, Magnesium and Age on Growth and Survival of Litopenaeus vannamei Post-Larvae Reared in Inland Low Salinity Well Waters in West Alabama

Abstract— The production of Litopenaeus vannamei in inland low‐salinity well water is a growing industry in several regions of the world. The state of Alabama in the southeastern USA is one such region with a large saline aquifer that could be utilized for shrimp culture. However, some farmers are experiencing problems rearing marine shrimp while others are having considerable success. Previous work has correlated low levels of potassium andor magnesium to poor shrimp survival. The problem is further complicated by the fact that the age at acclimation may also influence survival. In our present study, we evaluated the effects of potassium, magnesium, and the age of acclimation on growth and survival of PL at two farms. The first experiment was run in a static system utilizing four replicate tanks per treatment. Fifty PL₁₇ (0.0066 g) that had been acclimated to 4 ppt seawater were stocked into each tank and the following treatments evaluated: low salinity well water (LSWW) without mineral supplements, LSWW with KCl, LSWW with MgCl₂, and LSWW with KCl and MgCl, added to the water. Shrimp were harvested, counted and weighed after 4 wk. Survival was significantly higher in treatments receiving mineral supplements whereas biomass was only higher in the two treatments with potassium supplements. The second experiment was set up initially as a static system filled with 8.5‐ppt reconstituted sea water that was then converted to a flow‐through system using LSWW. This experiment evaluated the effect of PL age at acclimation on survival and growth at four different ages (PL₁₅, PL₁₉, PL₂₃, and PL₂₇). All tanks were stocked with 50 PL₁₃L. vannarnei. Two days after stocking, and then at 4‐d intervals, a series of four tanks were converted to flow through (rate of 40 Lhr) using LSWW. After acclimation, water flow was maintained in all tanks until 28 d after stocking when tanks were harvested and surviving shrimp were counted and weighed. Survival and growth increased with PL age when shrimp were acclimated to inland low salinity well water.     

不同放苗密度凡纳滨对虾生物絮团养殖的环境和产出效应

本研究尝试将生物絮团养殖技术(Bio-floc aquaculture technology, BFA)应用到凡纳滨对虾高密度养殖系统中,研究生物絮团在凡纳滨对虾不同放苗密度下的水质调控、对虾生长及存活等方面的作用效果。试验将200、400和600尾/m2的放苗密度分为传统养殖组(TF200、TF400和TF600)和絮团养殖组(BFA)(BF200、BF400和BF600)共6组,分别在18个室内水泥池中进行,其中BFA组通过添加益生菌和赤砂糖培养生物絮团,并在养殖过程中极少换水,而传统养殖组进行传统换水养殖管理。经过113d的养殖试验,随着放苗密度的增加,水质、对虾存活率和对虾特定增长率逐步下降,然而BFA在400尾/m2的凡纳滨对虾封闭式养殖中有良好效果。与400尾/m2的传统养殖组(TF400)相比,400尾/m2的BFA组(BF400)在养殖过程中生物絮团平均形成量提升3.25倍;水体中的亚硝酸氮和氨氮平均含量分别降低67.9%和72.7%,而用水量只有传统养殖组的33%左右;对虾的体重、存活率、特定生长率及单位产量分别提高了14.5%、156.3%、2.4%和194.1%;400 尾/m2的BFA组对虾单位产量达到4.01±0.94 kg/m2,具有最好的环境和产出效应。     

Comparing clear-water RAS and biofloc systems: Shrimp (Litopenaeus vannamei) production,water quality,and biofloc nutritional contributions estimated using stable isotopes

Indoor shrimp aquaculture systems can be used to produce fresh, never-frozen, quality shrimp near metropolitan seafood markets regardless of season and climate. However, questions still remain regarding what type of production system is best suited to maximize indoor production. In this project, two types of systems were compared: clear-water (CW) RAS and biofloc (BF) systems. Three, 1.36 m³ tanks were assigned to each of the two treatments; CW tanks had external settling chambers, two foam fractionators, and external biofilters, all operated continuously. BF tanks had settling chambers and one foam fractionator which were operated as needed to control solids accumulation. Shrimp weighing 0.42 g were stocked in all tanks at 250 m⁻³ and grown for 55 days. Ammonia and pH levels were significantly (P < 0.05) higher in the CW treatment, while nitrite, nitrate, and turbidity were all significantly higher in the BF treatment, although all parameters remained within acceptable ranges for shrimp growth. Shrimp mean harvest weight was significantly higher, biomass (kg m⁻³) was significantly greater, and FCR was significantly lower in the CW treatment; there were no significant differences in survival between treatments. Isotope levels indicated that shrimp in the BF treatment obtained a portion of the C (18-60%) and N (1-18%) in their tissues from biofloc material; however, this effect did not positively influence production in that treatment. By nearly eliminating solids from the water and using an external biofilter, substantially better water quality was maintained in the CW systems, which may have been a major contributor to the improved shrimp production in that treatment.     

Use of artificial substrates in the culture of Litopenaeus vannamei (Biofloc System) at different stocking densities: Effects on microbial activity,water quality and production rates

Although the use of artificial substrates can favor shrimp culture, some studies indicate that their presence in growth tanks does not improve water quality or the performance of the animals. One objective of this study was to evaluate whether the presence of artificial substrates modifies the microbial activity and the water quality of the culture of Litopenaeus vannamei with bioflocs. The substrate effects on the shrimp performance and the relationship between these effects and the stocking density/biomass of shrimp were also evaluated. The experiment consisted of four treatments: D238: 238 shrimp m⁻³; D238 + S: 238 shrimp m⁻³ + substrates; D473: 473 shrimp m⁻³; D473 + S: 473 shrimp m⁻³ + substrates. Twelve experimental units of 850 L were stocked with juvenile L. vannamei (2.6 g) that were grown for 34 days. The substrates did not appear to affect water quality since the concentrations of orthophosphate, ammonia and nitrite were not significantly different in tanks with or without substrates. The periphyton biomass was low and the biological activity on the substrates was not significant, indicating that the water quality variables were mainly controlled by the microbial community associated with the suspended bioflocs. The shrimp grown in the presence of the substrate exhibited greater weight gain (D238 + S = 1.40 ± 0.05 and D473 + S = 1.20 ± 0.04 g week⁻¹) than those grown without substrates (D238 = 0.73 ± 0.04 and D473 = 0.44 ± 0.13 g week⁻¹). The final biomass was 314% greater in the tanks with substrates. The shrimp survival was significantly higher in the tanks with substrates (93.9 ± 2.4%) than in the tanks without substrates (42.5 ± 35.9%). The results indicate that the substrates served to increase the surface area of the tank and to reduce the relative stocking density, which appears to reduce the stress levels of shrimp, indicated by higher shrimp performance. In tanks with higher biomass, where the negative effects of intensification were most severe, the presence of the substrates had a positive effect on the production indices.     

A technical solution to the mass-culturing of larval turbot

A 1000 litre recirculation system of eight cylindrical rearing tanks has been tested in three 40-day periods to determine its capacity for rearing larval turbot (Scophthalmus maximus L.).The larvae were fed on rotifers and Artemia nauplii, as well as mixed marine algae. Continuous artificial light of 1500–2000 lux was applied at the surface. The applied algae served a dual function; keeping rotifers and Artemia at a high nutritional level as well as effectively removing the released ammonia. The combination of upwelling water and light at the surface maximized the contact surface between larvae, food items and algae.With this system, using a stocking density of 16 larvae litre^?1 in the rearing tanks, a survival total of 40% at Day 40 was achieved, giving a production of 6·4 larvae litre^?1 or 3000 larvae metre^?2 of the surface of the rearing tanks.