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An Update on Dr. Tzachi Samocha’s Research

 

 

 

Dr. Tzachi Samocha, a Regents Fellow and Professor at the Texas A&M AgriLife Research Mariculture Lab in Flour Bluff, Texas, USA, conducts research on super-intensive, zero-exchange, biofloc shrimp farming systems.  He hopes to develop a commercial system that could be located close to inland urban markets in the United StatesIn biofloc systems, bacteria gobble up shrimp waste products and create a nutritious food chain that the shrimp feed on.  What could be more beautiful than that? In the fall of 2012, Samocha completed two new studies on his system.

 

 

Feed Study

 

The first study reports on the results obtained from six, 40-cubic-meter, zero-exchange, high-density (500 shrimp/m3) raceways in which two commercial feeds were compared.  The results showed high yields, good growth and low feed conversion ratios (FCRs) for one of the feeds.  The following is a summary of the study that Samocha prepared for Zeigler Bros., a shrimp feed producer in Gardners, Pennsylvania, USA, one of the sponsors of Samocha’s research.

 

 

Use of limited discharge recirculating aquaculture systems can reduce disease introduction and the potential negative environmental impact created by traditional pond culture where extensive water exchanges are being utilized.  In recent years studies at the AgriLife Research Mariculture Lab have focused on the use of a specially designed diet (HI-35) made by Zeigler Bros. and formulated for use in biofloc-dominated, super-intensive, zero-exchange systems.  These systems have high stocking densities (greater than 300 shrimp/m3) resulting in high biomass (greater than 3-6 kg/m3).  A 2009 study at the lab showed that high yields (9.29 kg/m3) and survival (88%) can be achieved with no water exchange and a density of 500 shrimp/m3 while using foam fractionators or settling tanks (STs) to regulate levels of particulate matter in the culture medium.

 

Objectives

 

1. Study the effect of two commercial diets on shrimp performance and selected

water quality indicators under zero water exchange

2. Monitor shrimp growth, survival and FCR under zero water exchange

3. Produce market-size Litopenaeus vannamei at a high stocking density

with zero water exchange

4. Evaluate the benefit of using continuous dissolved oxygen-monitoring equipment

in operating a super-intensive shrimp production system.

 

The study was conducted in six 40-m3 raceways.  Each 25.4 x 2.7 (68.5 m2) raceway was lined with EPDM (ethylene oropylene diene terpolymer, Firestone Specialty Products, Indianapolis, Indiana, USA), a liner previously determined to be non-toxic to shrimp.  Raceways were equipped with a center longitudinal partition positioned over a 5.1 centimeter PVC pipe with sprayer nozzles.  Each raceway had six banks of three 5.1 cm airlift pumps positioned equidistance on both sides of the partition.  In addition, each raceway had six 0.91 cm long air diffusers (1.9 cm OD, Aero-Tube™, Tekni-Plex Aeration, Austin, Texas, USA), a 2 HP centrifugal pump and a Venturi injector capable of introducing atmospheric air or a mixture of oxygen and air.  Raceways were filled with 18 m3 of water used in a preceding 49-day nursery study and another 22 m3 of natural seawater and municipal freshwater.  Each raceway was equipped with a small commercial foam fractionator (VL65, Aquatic Eco-System, Apopka, Florida, USA) and a homemade settling tank (ST).  Shrimp used in this study were produced from a cross between Taura-resistant and fast-growth genetic lines developed by Shrimp Improvement Systems.  Two shipments of postlarvae (PLs) were delivered via overnight-air eight days apart.

 

Postlarvae received on April 12, 2012 (the 1st shipment) were cultured at low density (1,000 PL/m3) in the same 40 m3 raceways described earlier.  Postlarvae received on April 20, 2012 (the 2nd shipment) were stocked in two 20 m3 circular tanks at a higher density (3,000/m3).  Each raceway in the growout study was stocked with an equal number of juveniles originating from these two nursery systems.  The first stocking of the six growout raceways took place on June 1, 2012, using shrimp from the 1st shipment.  A total of 12,000 juvenile shrimp (3.74 grams each) were stocked in the raceways.  The second stocking was done on June 6, 2012, with 8,000 juveniles (0.9 grams) from the 2nd shipment stocked into each raceway, bringing the total number of shrimp stocked in each raceway to 20,000 or 500/m3.  The mixing of juveniles from the two nursery systems resulted in a reduction of the mean average weight of the shrimp to from 3.74 to 2.66 grams.

 

This study compared two feeds with three replicates each.  The semi-intensive diet (SI-35) was formulated to contain 35% crude protein, 7% lipid and 4% fiber and the hyper-intensive diet (HI-35) 35% crude protein, 7% lipid and only 2% fiber, both produced by Zeigler Bros.  Raceways 2, 4 and 6 received the SI-35 diet, while raceways 1, 3 and 5 received the HI-35 diet.  Shrimp were fed by hand for the first three days and by using a combination of hand-feeding and automatic belt feeders for days 4 to 11.  From day 12 to 47, feed was delivered by belt feeders over a 12-hour period.  Beginning with day 48, shrimp were fed over a 24-hour period using belt feeders.  For the first month daily rations were based on an assumed growth of 1.5 grams per week, a feed conversion ratio of 1.4 and mortality of 0.5% a week.  Rations were later adjusted based on observed feed consumption and results of the twice weekly shrimp sampling, where growth was eventually adjusted up to 2.56 grams a week.  Use of the foam fractionators and the settling tanks was initiated 7 and 44 days, respectively, after the study began.  Foam fractionators and settling tanks were operated intermittently, targeting total suspended solids (TSS) concentrations between 200 and 400 milligrams per liter and settleable solids between 10 and 12 milliliters per liter.  Settling tank flow rates varied between 8.5 and 12 liters a minute.

 

Raceways were maintained with zero water exchange throughout the study and municipal freshwater was added to compensate for water losses due to evaporation and operation of the foam fractionators and settling tanks.  Water temperature, salinity, dissolved oxygen and pH were monitored twice daily using a YSI 650 Series multi-probe (YSI Inc., Yellow Springs, Ohio, USA).  Settleable solids were monitored daily.  Alkalinity was measured twice a week; TSS was monitored three times a week, while turbidity, volatile suspended solids (VSS), carbonaceous biochemical oxygen demand (cBOD5), total ammonia nitrogen (TAN), nitrogen (NO2), nitrogen (NO3) and phosphate (PO4-P) were monitored weekly.  Each raceway was equipped with a YSI 5500 multi-parameter monitoring and alarm system with an optical dissolved oxygen probe (YSI Inc., Yellow Springs, Ohio, USA).  Data collected by the monitoring system was uploaded into a computer in the lab that could also be accessed from remote locations for real-time monitoring of the dissolved oxygen in the six raceways.  Daily and weekly water quality data from the two treatments was analyzed by linear mixed models.  Shrimp mean final weights, weekly growth rate, survival, feed conversion ratio, and total yields were analyzed using one-way ANOVA.  A significance level of p<0.05 was used for all statistical tests.  Oxygen supplementation was initiated on day 17 and continued until the end of the 67-day study.  From day 17 until day 38, supplementation was related to daily events (e.g., feeding, molasses addition).  Beginning on day 39, when shrimp biomass was estimated to be 6 kilograms per cubic meter, supplemental oxygen was used 24 hours a day at a flow rate of 3.4–8.2 liters per minute due to low dissolved oxygen in the raceways.

 

The YSI 5500 monitors and their optical probes proved to be a valuable tool for the management of super-intensive shrimp culture, allowing quick adjustments to be made to minimize stress from low dissolved oxygen while setting upper and lower dissolved oxygen limits helped to optimize oxygen use.  Table 1 and 2 (below) summarize the mean values of daily and weekly water quality indicators monitored in this study.  There were no statistically significant differences in dissolved oxygen, temperature, salinities, pH, TAN, NO2-N, NO3-N, PO4, cBOD5 and SS between treatments.  Total ammonia nitrogen levels remained below 0.5 milligrams per liter throughout the study while NO2-N levels remained below 1.22 milligrams per liter with no significant differences between treatments.  While solids were controlled by the use of the foam fractionators and settling tanks, TSS, turbidity and VSS levels in the SI-35 treatment remained significantly higher than the HI-35 treatment.  These results may be related to the higher levels of non-digestible components contained in the SI-35 as determined by analyses made by New Jersey Feed Lab (feed fiber of 2.69% vs. 1.61%) and ash (11.11% vs. 9.55%) than HI-35.  Sodium bicarbonate was initially added to raceways based on past experience (equivalent to ~20% the weight of the feed) to target 160 milligrams per liter calcium carbonate (CaCO3).  The HI feed, however, did not reduce the alkalinity at the same rate experienced with the SI-35 feed.  This quickly led to a separation in alkalinity between treatments due to the initial overcompensation in the HI-35 treatment.  By week 5 the alkalinity levels in the two treatments were similar again.  The total bicarbonate supplementation in the SI-35 raceways averaged 53.6 kilograms and only 41.6 kilograms in the HI-35 treatment.  Oxygen use for the HI-35 treatment was 21% lower compared to the SI-35 treatment and the volume of water used to produce 1 kilogram of shrimp was slightly lower for the HI-35 treatment than the SI-35 (125 per liter vs. 138 per liter, respectively, Table 3).

 

 

 

Analyses of shrimp performance based on harvest data (Table 3, below) showed significantly better mean final weights (22.33 vs. 19.79 g), yields (9.75 vs. 8.71 kg/m3), weekly growth (2.03 vs. 1.76 g/wk) and FCR (1.25 vs. 1.43) of the shrimp fed the HI-35 diet.  No statistically significant differences were found between treatments in survival (87.27% for HI-35 vs. 88.18% for SI-35) however shrimp survival in all raceways was lower than experienced in previous trials.

 

 

This study showed that market size shrimp can be produced with zero water exchange and although the cost difference between the HI and SI feeds is significant ($1.75/kg vs. $0.99/kg), a preliminary economic analysis of profitability indicates that both feeds would be commercially viable with the profit advantage in favor of the HI feed.

 

Acknowledgements: We would like to thank CSREES, USDA Marine Shrimp Farming Program and Texas A&M AgriLife Research for funding this study.  Also, Shrimp Improvement Systems, Islamorada, Florida, USA provided the postlarvae at reduced cost, Zeigler Bros., Gardners, Pennsylvania, USA, donated the feed, YSI Inc., Yellow Springs, Ohio, USA, donated the YSI 5500 multi-parameter monitoring systems, Aquatic Eco System, Apopka, Florida, USA, donated the foam fractionators, Tekni-plex Aeration, Austin, Texas, USA, donated the Aero-Tube™ diffusers, and Firestone Specialty Products, Indianapolis, Indiana, USA, donated the raceway liners.

 

 

Research in Two 100 m3 Raceways with “a3” Aeration

 

Losses due to viral disease outbreaks and the potential negative impact from nutrient-rich water on receiving streams are two major challenges for the development of sustainable, biosecure and cost-effective shrimp farming practices.  Use of greenhouse-enclosed, super-intensive, biofloc-dominated, zero-exchange systems may alleviate these problems; however, operating biofloc systems at high production levels (greater than 6 kg/m3) requires substantial inputs to satisfy the high oxygen demand of the shrimp and the microbial communities.  Previous studies at the Texas A&M AgriLife Mariculture Lab utilized a pump driven Venturi to inject air and/or pure oxygen into a central manifold along the raceway bottom to mix and aerate the water while additional circulation and mixing was provided by airlifts and air diffusers.  This system has worked well for numerous studies in the past, producing 8-9 kg/m3 of marketable size shrimp.  In 2010, however, in an effort to reduce production costs (e.g., oxygen supplementation, electricity use) our lab began testing non-Venturi injectors for aeration and mixing in 100 m3 biofloc raceways.  These injectors (All Aqua Aeration's “a3” system, Orlando, Florida, USA) are currently used in several wastewater treatment facilities in the USA and require little maintenance compared to other aeration methods.  This technology may be successfully transferred to biofloc and other types of aquaculture systems.  According to the manufacturer’s specifications the injector provides a 3:1 air to water ratio.  In contrast, our current Venturi system provides less than a 1:1 ratio and requires use of supplemental oxygen at high biomass loading (greater than 6 kg/m3) to maintain the desired dissolved oxygen (DO) levels.  The 2010 trial was conducted in two 100-m3 raceways and resulted in the production of 6.4 kg shrimp/m3 at harvest while a subsequent 2011 trial resulted in 8.4 kg/m3.  In both cases the injectors were able to provide adequate mixing throughout the water column, eliminating the need for peripheral aeration devices (e.g., an air blower, air diffusers and airlift pumps).  Although FCRs in both of these trials were unusually high, 2.46 and 1.77, respectively, and some oxygen supplementation was required during the 2011 trial, we were confident that we could increase production, reduce FCRs and reduce or eliminate oxygen supplementation in future production trials.

 

 

Objectives

 

1. Evaluate the performance of fast-growth shrimp from Shrimp Improvement Systems

stocked at 500 shrimp/m3 and fed a commercial feed formulated for high-density

minimal water exchange culture systems.

2. Further evaluate the ability of the injectors to maintain adequate dissolved

oxygen (DO) levels and mixing in a zero-exchange, super-intensive raceway system.

 

In addition to these objectives, we hoped to reduce FCRs below those achieved in the previous trials, primarily through continuous feeding (24 hours a day), anticipating that this strategy would also eliminate dramatic feed related drops in DO levels and decrease the need for supplemental oxygen.

 

The current 63-day growout trial was conducted in two 100 m3 EPDM-lined raceways.  To provide aeration and mixing, 14 non-Venturi injectors were positioned parallel to the direction of flow along the bottom of each raceway wall.  The system may be operated using a single 2-HP pump or when conditions dictate (e.g., high biomass, solids loading, low DO) two such pumps working concurrently.  To enable the removal of particulate and dissolved organic matter each raceway had one additional injector to power a homemade foam fractionator and a simple 2 m3 conical settling tank.  Raceways were initially filled to 72 m3 with a mixture of seawater (23 m3), municipal chlorinated freshwater (24 m3) and biofloc-rich water (25 m3) from a previous nursery study.  Whereas the juvenile shrimp (3.14 grams) in the 2011 study were of a Taura-resistant strain and stocked at 390 juveniles/m3, the shrimp used in the current study were a cross produced from Taura-resistant and fast-growth genetic lines (from Shrimp Improvement Systems), and juveniles (3.60 grams) were stocked at 500 shrimp/m3.  Shrimp were fed a 35% crude protein diet (Hyper-Intensive-35, Zeigler Bros., Gardners, Pennsylvania, USA) seven days a week using four 24-hour belt feeders in each raceway.  On day 7, raceways were filled to capacity (100 m3) with a mixture of 14 m3 freshwater and 14 m3 saltwater.  Initial daily rations were based on an assumed FCR of 1:1.4, growth of 1.5 grams a week and mortality rate of 0.5% a week.  Rations were later adjusted based on results of twice-weekly shrimp growth sampling and feed consumption observations.  Raceways were maintained with no water exchange and freshwater was added weekly (equivalent about to 0.475 m3 a day) to maintain salinity and compensate for water losses associated with operating the foam fractionators and the settling tanks.  Water temperature, salinity, dissolved oxygen and pH were monitored twice daily using a YSI 650 Series multi-probe (YSI Inc. Yellow Springs, Ohio, USA).  Each raceway was also equipped with a DO monitoring and alarm system (YSI 5200, YSI Inc., Ohio, USA) to enhance DO management.  Alkalinity was measured twice a week and adjusted to 160 mg/L (as CaCO3) using sodium bicarbonate.  Settleable solids (SS) were measured daily and TSS were monitored at least twice a week.  Turbidity, VSS, cBOD5, TAN, NO2, NO3, and PO4-P were monitored weekly.  Tables 1 and 2 (below) summarize the daily and weekly water quality indicators.  Mean water temperature, salinity, DO, and pH were 29.6°C, 29.3 ppt, 5.5 mg/L and 7.1, respectively.  TAN and NO2-N remained low throughout the study, less than 0.6 mg/L and less than 1.5 mg/L, respectively, and NO3-N levels increased from 67 mg/L at stocking to an average of 309 mg/L at harvest.

 

Foam fractionators (FFs) were started on day 8, and the use of the settling tanks began on day-23 when suspended solids (SS) reached 23 ml/L in one of the raceways.  The flow rate for the FFs was 28 liters per minute while in the STs flows ranged from 8.5-20 liters per minute.  Both methods of solids removal were used intermittently and mean TSS and SS levels (Table 2) were 292 mg/L and 12 ml/L, respectively.

 

Minor mortality was observed beginning the third week of culture, so supplemental oxygen was provided on day 22 to alleviate potential stress and hopefully stop the mortalities.  Supplemental oxygen had no perceptible effect on mortality and on day 44, when biomass was estimated to be about 8.2 kg shrimp/m3, the second 2-HP pump was engaged to increase aeration.  Oxygen supplementation was discontinued three days later.

 

On Day 64 shrimp were harvested using a mechanical harvester (Magic Valley Heli-Arc & Mfg., Inc., Twin Falls, Idaho, USA).  Mean final shrimp weights were 22.72 grams, and shrimp grew an average of 2.12 grams per week, yielding an average 903 kg per 100-m3 raceway (Table 3 below).  Survival was moderate (79.5%), however, mean production levels in the current study were greater than 2011 (9.03 vs. 8.4 kg/m3), and FCR was also reduced (from 1.77 to 1.48).

 

 

 

The injectors were able to maintain adequate DO levels and mixing for the production of marketable size shrimp in a biofloc dominated system with a substantial biomass load (greater than 9 kg/m3), maintaining dissolved oxygen levels in the two raceways above 5 mg/L (83-86% saturation) in most cases.  Although supplemental oxygen was eventually deemed unnecessary in the current study, supplementation was reduced by about 15% over 2011 despite higher biomass (8.4 vs. 9.03 kg/m3).  Continuous 24-hour-a-day feeding seems to have eliminated low DO events observed following hand feeding in the past and may have contributed to lowering the FCR.

 

The major development of the current study was the reduction of the production cycle from 106 days in 2011 to 63 days in 2012 due to sustained weekly growth of greater than two grams a week.  Clearly the use of shrimp from the fast-growth genetic line can significantly increase the number of potential crops per year making these systems more economically viable.

 

Information: Tzachi M. Samocha, Ph.D., AgriLife Research Mariculture Laboratory, 4301 Waldron Road, Corpus Christi, Texas 78418, USA (phone 1-361-937-2268, email tsamocha@ag.tamu.edu, webpage http://ccag.tamu.edu/mariculture-flour-bluff).

 

Sources: 1. A Summary Report Prepared for Zeigler Bros.  Comparison of Two Commercial Diets for the Production of Marketable Pacific White Shrimp, Litopenaeus vannamei, in a Super-Intensive, Biofloc-Dominated, Zero-Exchange Raceway System.  Tzachi Samocha, Timothy Morris, Vita Magalhães and André Braga.  Received at Shrimp News International on October 16, 2012.  2. Production of Marketable Size Pacific White Shrimp, Litopenaeus vannamei, Fed a Commercial 35% Crude Protein Diet Formulated for Use in Super-Intensive, Biofloc-Dominated, Zero-Exchange Raceway Systems.  A Summary Report.  Tzachi M. Samocha, André Braga, Vita Magalhães, Bob Advent and Timothy C. Morris.  November 7, 2012. 3. Bob Rosenberry, Shrimp News International, November 27, 2012.

 

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