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United States Department of Agriculture

Agricultural Research Service

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Location: Warmwater Aquaculture Research Unit

2011 Annual Report

1a. Objectives (from AD-416)
1. Develop and test novel equipment and strategies to increase gas exchange and the efficiency of fish production while minimizing equipment and energy costs. 2. Develop acoustic technology and methodologies to improve the production and profitability of aquaculture in the United States. 3. Determine effectiveness of new germplasm and novel aeration technologies on commercial scales.

1b. Approach (from AD-416)
We have made great strides in understanding the relationships between dissolved oxygen, feed consumption, feed conversion, growth, production and susceptibility to disease, and we will continue to learn more about the impacts of oxygen on fish health, development, growth, and production economics. However, we have learned enough to shift our focus to applications – development, testing and tech transfer of new equipment and techniques to improve oxygen management efficiency in both hatchery and pond systems. We havealso learned a good deal on the use of active SONAR systems to observe and quantify food sized and larger fish in the acoustically complex environment of commercial ponds. We will continue to improve our understanding of this field but will expand it to include other acoustic applications. Acoustic sounds, both from catfish and man-made sources, will be introduced into ponds to determine if the fish can be made to respond in a predictable, desirable manner to improve seining. One of the main objectives of CRIS 6402-31000-008-00D (Catfish Genetics, Breeding, and Physiology) is to “Initiate development of channel catfish and blue catfish germplasm with improved growth, yield, and esc resistance for eventual transfer to commercial producers”. This CRIS has been tasked with developing a procedure that will be used for future on-farm testing and preliminary commercial evaluation of new lines before full-scale release to the industry. Once in place, this model could also be used for assessment of new aeration or pond monitoring equipment, chemical treatments, vaccines, and algal control methods.

3. Progress Report
Research focuses on design and testing of a new catfish egg incubator, management techniques to increase catfish fry survival, improved oxygen management and production efficiency in catfish production ponds, development of new aeration technology, and new uses for active and passive acoustic techniques. Work continued on testing of the see-saw incubator at a collaborating commercial catfish hatchery. Research compared survival through swim-up stage in see-saw incubators either with or without supplemental oxygen supplied through diffusers in each trough. Survival through swim-up stage averaged 71.2% overall and was not significantly different between treatments. These results confirm that at least 45 pounds of eggs can be incubated in the see-saw without supplemental oxygen if the dissolved oxygen concentration of the supply water is at approximately air saturation. In FY2010 a field trial of an in-pond confinement system for short-term (2-3 week) culture of catfish fry before they are released to the open pond was conducted. This technique was examined as a means of improving overall fry survival rates in large ponds, and may provide an opportunity to vaccinate slightly larger (and more immune-competent) fish. While not statistically relevant (N=2), the two commercial ponds using confinement for a pre-growth period had a higher survival and produced larger fingerlings than did the two control ponds. A third year of research on oxygen requirements of blue X channel hybrid catfish in pond production systems was completed and indicates that hybrid catfish consume more feed at lower dissolved oxygen concentrations than channel catfish, and should convert feed better due to reduced mortality. This can result in significant energy and feed savings by the industry as they move to hybrid catfish production. Work on development of the U-tube aerator has progressed with the recruitment of a HQ-funded post-doctoral research associate. An air-lift system is now being tested as a more efficient means of moving and aerating water with the u-tube system. A patent application for this device has been submitted through ARS. Work progressed on the use of a sonicator as a “green” method to reduce pond populations of ram’s horn snails, an intermediate host to the catfish trematode. If this is successful, use of chemical controls such as copper sulfate or hydrated lime will not be necessary. Work is beginning on a project aimed at increasing fry survival and decreasing production costs through fingerling stage. Use of supplemental oxygen may improve survival and growth, and allow for production of catfish fry at much higher densities in the hatchery prior to stocking in open ponds. Supplemental oxygen may thus reduce the need for heated well water in the hatchery, conserving both water and energy.

4. Accomplishments
1. Development of the see-saw catfish egg incubator. Traditional paddle-type catfish egg incubators have served the industry well for nearly a century but require a high water exchange rate and lose efficiency at egg loading rates above 6.8 kg (15 lbs) per trough. ARS researchers at Stoneville, Mississippi, in collaboration with industry partners, have developed a new incubator (the see-saw) which can incubate more eggs using less water and labor. In a direct comparison at a similar egg-loading rate (11.8 kg per trough), the see-saw produced 2.3 times as many viable swim-up fry as the traditional incubator. Additional studies indicate that over 20 kg of eggs/trough can be hatched in the see-saw using only 8 liters per minute of water with no negative impact on hatch rate, saving considerable labor, space, ground water, and energy for pumps and heaters. In commercial field trials thus far over 150 M egg have been hatched. Upon completion of the field trials, technology transfer plans are expected to result in rapid adoption by the catfish industry as well as by public-sector hatcheries which are typically space-limited.

2. Improved catfish feed conversion through pond oxygen management. Dissolved oxygen is assumed to be the most critical water quality parameter in warmwater aquaculture but controlled studies of the impact of this diurnally-fluctuating parameter on channel catfish have been lacking. ARS researchers at Stoneville, Mississippi, are concluding a long-term research program examining the impact of pond DO (dissolved oxygen) concentrations on blue, channel, and blue X channel catfish growth, production, food consumption and food conversion. These studies were made possible by the use of a computer-controlled pond oxygen monitoring system which could initiate aeration at precise DO set-points and continuously record DO, temperature and aerator usage. Results with all three species show that higher DO concentrations than previously thought (best performance at minimum daily DO concentrations of 2.5-3.0 mg/L) are required for optimum food conversion and growth, and this improved growth will significantly shorten the production cycle (currently three to five years) down to two years from egg to food fish. While food conversion is not directly impacted by DO except at extremely low DO concentrations, a shorter production cycle reduces fish losses to all causes, significantly improving food conversion. Feed is the greatest single cost in catfish production. Increased growth resulting from improved DO management can reduce food conversion ratios from an estimated industry-wide 2.5-3.0:1 to 2.0:1, reducing production costs by $0.10-0.20/lb, greatly improving the profitability of catfish farming.

3. Extended culture of catfish fry to improve survival to fingerling stage. Catfish fry are typically raised in hatcheries for only a day or two past swim-up and then are stocked in 10-acre ponds for growth to fingerling stage. Initial survival is dependent on the insect predators and zooplankton species and density and can be highly variable. Continued confined culture for a week or two could result in advanced fry large enough to both eat pelleted feed and escape insect predation. Swim-up fry were stocked in fine-mesh net pens made with 150 ft block-off nets located in two designated 7.6-acre fingerling ponds at a rate of approximately 100,000/acre. Two similar control ponds were stocked on the same dates. Fry were fed several times daily with a commercial fry feed for several days and were gradually switched to a small-diameter floating feed. Aeration and circulation maintained water quality for the two week culture period prior to release in the pond, by which time the fry had grown large enough to consume small floating pellets. While not statistically relevant (N=2), the two ponds using the net pens for a pre-growth period had a higher survival and produced larger fingerlings than did the two control ponds. Continued culture of catfish fry, particularly fry of blue X channel catfish hybrids which are over twice as valuable as pure channel catfish fry, may be feasible, allowing farmers to consistently produce more fingerlings without added cost.

4. Development of improved aerator. Paddlewheel aerators have been used for aeration in aquaculture for over 25 years. They add a lot of oxygen but also distribute a large volume of water which dilutes the aeration effort over the entire pond volume. Thus, a great deal of equipment and a large amount of power is required to prevent low DO (dissolved oxygen) conditions. ARS researchers at Stoneville, Mississippi, have developed a new aerator, Power Tube Airlift (PTA) which can concentrate DO into a small zone of water in a pond using less energy than traditional methods. Aeration efficiency tests were conducted on the device at a variety of water depths and electric motor speeds (rpm) to determine SOTR (standard oxygen transfer rate) and SAE (standard aeration efficiency). Water velocity was also measured to determine water flow rate and pumping efficiency. At an air injection point (sparger water depth) of 6 m (20ft), SOTR and SAE ranged from 4.8-9.6 kg O2/h (10.6-21.1 lb O2/h) and 1.3-1.9 kg O2/kW·h (2.1-3.1 lb O2/hp·h), respectively. Water flow rate and pumping efficiency ranged from 25.2-40.3 m3/min (6,660-10,658 gpm) and 5.5-9.3 m3/min/kW (1,075-1,831 gpm/hp), respectively. Additionally, when initial DO concentrations were lowered to 0.0 mg/L to simulate a total bloom die-off, the outflow water from the PTA produced DO concentrations of approximately 2.70 mg/L. This aerator was an Active Invention as of 04/12/2011 (Docket No: U0110.11). By concentrating the aeration effort into a smaller area of the pond, emergency aeration efficiency would likely exceed that of a paddlewheel aerator. Fewer moving parts and improved efficiency would reduce the costs associated with repair and maintenance, and lower power (electricity) consumption, respectively.

5. Development of an ultrasonic system to control nuisance species. The ram’s horn snail acts as a host to trematodes which markedly reduce the profitability of commercial catfish farming. Traditional treatment involves copper sulfate or hydrated lime to kill the snails and break the trematode lifecycle. Developing an acoustic control technique would provide a green alternative to the use of caustic chemicals. Scientists with the University of Mississippi’s National Center for Physical Acoustics in Oxford, Mississippi, in collaboration with scientists at the National Warmwater Aquaculture Center in Stoneville, MS, are pursuing the use of high amplitude ultrasonic signals to kill the ram’s horn snail. Initial laboratory tests using a commercially available sonicator used for welding plastic is capable of killing individual snails in aquaria nearly instantaneously. Tests with lowered sound power levels to mimic pond absorption showed lower efficacy rates. Work is underway to alter the operating parameters of the sonicator to see if higher power levels are possible and if alternate driving frequencies can provide some benefit. Alternate approaches to achieve more output in the pond would be the use of multiple sonicators in conjunction with a focusing device (parabolic dish or semi-cylinder submerged in the water) to re-create some of the reverberation achieved in the lab testing. Such a device could be attached to a vehicle which carries the electrical power generation in the envisioned field delivery device. This work could lead to improved profitability by eliminating nuisance species without the use of chemicals.

Review Publications
Brown, T.W., Chappell, J.A., Boyd, C.E. 2011. A commercial-scale in-pond raceway system for ictalurid catfish production. Aquacultural Engineering. 44:72-79.

Last Modified: 05/24/2017
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