Location: Warmwater Aquaculture Research Unit
2018 Annual Report
Objectives
The overall objective of this project is to increase profitability of catfish aquaculture by improving farm-level production efficiency. This will be accomplished by developing new production systems and management practices that allow greater control of the culture environment, with the end result that the genetic potential of catfish can be fully expressed. Studies will also be conducted on the use of ultrasound to kill the intermediate host of an important catfish pathogen and reduce bacterial loads in processing plant cold-water washes. Over the next 5 years, we will accomplish the following objectives:
1) Enhance Control of Pond-Based Ecosystems to Maximize Production and Product Quality.
Sub-objective 1.1 Optimize split-pond design for food-sized catfish aquaculture.
Sub-objective 1.2 Maximize catfish production potential of conventional ponds using intensive aeration.
Sub-objective 1.3 Evaluate management practices to reduce the final size variation resulting from variable growth rates in hybrid catfish.
2) Determine the Suitability and Feasibility of Polyculture or Off-season Production of Other Species Using Catfish Culture Infrastructure.
Work on this objective will focus on developing technologies for production of a secondary, non-catfish species, such as tilapia, in split-ponds. Production of secondary filter-feeding species can potentially increase on-farm profits by generating an additional crop at little extra expense and may improve water quality in split-pond systems by feeding on plankton and detritus that are an oxygen-consuming waste product in catfish monocultures.
3) Develop Acoustic Technology and Methodologies to Improve the Production and Profitability of Pond-based Aquaculture in the United States.
Sub-objective 3.1 Develop and test the potential for control of ramshorn snails in ponds using ultrasound.
Sub-objective 3.B. Develop and test the potential for ultrasound to reduce bacteria in the cold-water wash in processing plants.
Work on this objective will be conducted using congressionally mandated funds administered through Specific Cooperative Agreement 58-6402-9-427 (“Development of Active and Passive Acoustic Measurements to Improve Production and Profits of U.S. Aquaculture”) between the ARS Warmwater Aquaculture Research Unit, Stoneville, MS, and the National Center for Physical Acoustics, at the University of Mississippi. Under this Agreement and as part of this Project Plan, novel application of acoustic technology will be tested and developed, including Sub-objective 3.A, developing and testing the potential for control of ramshorn snails (a disease vector in catfish ponds) using ultrasound, and Sub-objective 3.B, reducing bacteria in the cold-water wash in catfish processing systems using acoustic cavitation.
Approach
Four, 7-acre earthen ponds at the National Warmwater Aquaculture Center at Stoneville, Mississippi, will be modified into split-ponds (Sub-objective 1.A). Pump-performance curves will be developed by systematically changing pump operational parameters for four pump types—one pump for each split-pond. High aeration rates will be used to culture hybrid catfish (channel catfish x blue catfish) and measured variables will include fish growth, survival, production, processing yield, feed conversion ratio, dissolved oxygen concentrations, and water quality variables measured biweekly. Relationships among average flow rate (pump type) and fish growth, feed conversion ratio, and selected water quality variables for each year over the 3-year study will be assessed using regression analysis and results will yield different options for farmers using this technology in the industry.
Six, 0.25-acre ponds with 24 horsepower/acre of aeration for hybrid catfish production will be used in this study (Sub-objective 1.B). Dissolved oxygen, temperature and aerator status will be continuously monitored and the aerators controlled using a pond oxygen monitoring and control system already in place. Water quality will be measured biweekly for hybrid catfish production. Response variables will include final fish weight, weight gain, net production, processing yields, survival, feed consumed, feed conversion ratio, aerator usage), and economics Relationships among stocking rate, aerator usage, feed consumed, weight gain, feed conversion ratio, and selected water quality variables will be assessed using regression analysis. This model should allow us to recommend a stocking rate that will allow satiation feeding through the growing season and will be tested on commercial ponds.
Twelve, 1-acre ponds (10-hp of aeration per acre) will be used to produce hybrid catfish at the Delta Branch Experiment Station, Stoneville, MS (Sub-objective 1.C). Production parameters, coefficients of variation in size, and final economics will be compared among treatments using analysis of variance. Pending the results from this study, further studies on hybrid catfish foodfish management practices to reduce growth rate variation, including feeding schedules and practices, will be conducted.
For Sub-objective 2, a 4.5-acre split-pond aquaculture system located at the National Warmwater Aquaculture Center in Stoneville, Mississippi will be modified for to allow for the production of hybrid catfish and Blue Tilapia. Production performance will be measured and a performance average will be taken after three production seasons and a partial budget developed to measure gauges of economic efficiency of this production method as compared to conventional split-pond catfish aquaculture.
Experiments will be conducted on groups of snails using a commercially available sonicator as the acoustic source to destroy snails (Sub-objective 3.A). The potential use of ultrasonic cavitation to reduce bacteria in the cold-water wash in processing plants will be investigated as well in Objective 3.B. A cost-benefit comparison must be made to determine if the proposed design and technique is warranted.
Progress Report
The focus of this project is to develop a more complete understanding of the impacts of water quality, particularly dissolved oxygen and ammonia, on economics, growth and production of channel and hybrid catfish, and to develop new equipment, production systems and management strategies to utilize that information. The ultimate goal is to reduce the production costs for American fish farmers, making them more competitive in a world economy and providing quality fish to American consumers at a fair price.
Most warm water aquaculture research in the United Stated has been conducted in small (0.10-0.25-acre) ponds. Results are then presented to catfish farmers, assuming in most cases that farmers will observe the same relative results in larger (0.3-20-acre) commercial ponds. Agriculture Research Service (ARS) scientists in Stoneville, Mississippi, with collaborators from Mississippi State University, are producing hybrid catfish at two stocking rates (5,000 and 15,000 fish/acre) in small (0.25-acre), medium (2.0-acre) and large (4.0-acre) earthen ponds. Results, when available, will shed light on the application of small-pond research to commercial ponds.
Microbial phytase (FT) is one of the most studied additives in fish diets. Phytase breaks down phytic acid or its salt, phytate, inherent in plant feed ingredients and releases inorganic phosphorus as PO43- which is readily absorbed by fish. Rather than a standard phytase dose, typically about 500 FTU/kg, there is renewed interest in 6-phytase “super-dosing” in animal feeds in an attempt to more quickly and completely hydrolyze phytic acid into PO43- in the early stages of digestive process. Recent reports from the swine and poultry industries show phytase super-dosing at 2,500 FTU/kg and above further improves feed consumption, growth, food conversion ratio (FCR), and the absorption of phosphorus and other minerals over a standard dose. If effective in catfish, it is believed that phytase super-dosing may help alleviate losses associated with catfish anemia, a major disease in catfish production. Two experiments were conducted by ARS scientists at Stoneville, Mississippi, in collaboration with scientists from Mississippi State University to evaluate responses of hybrid catfish, female Ictalurus punctatus × male Ictalurus furcatus, to “super-dosing” of 6-phytase added to existing commercial catfish feeds. In each experiment, two diets with or without a phytase super-dose (2,500 and 5,000 phytase units [FTU]/kg, respectively) were compared. Phytase super-dosing does not appear to have additional benefits beyond the standard dose, at least on promoting growth and preventing anemia in catfish, and also had no beneficial effects on water quality. Ongoing technology transfer efforts recommend 500 FTU/kg phytase and not “super-dosing” to replace inorganic phosphorus in catfish feeds.
ARS at Stoneville, Mississippi, previously determined that channel catfish egg masses require ambient water with over 95% air saturation to maintain maximum oxygen consumption and optimum development as they near hatch. Since hybrid catfish eggs are often kept separated after fertilization by the addition of fuller’s earth and incubated in large vertical tube incubators, it is assumed but not known for sure that the critical oxygen requirement is lower. A study conducted by Agriculture Research Service scientists in Stoneville, Mississippi, determined the critical dissolved oxygen (DO) concentration for incubation of hybrid catfish eggs. The maximum (DO) required by hybrid catfish eggs increased throughout the incubation period, peaking at 79% air saturation during the last two days of incubation. Sac fry require approximately 55% saturation for the first two days post-hatch. It is recommended that hatchery managers maintain DO above 80% during the last two days of incubation.
The single-batch production strategy common with hybrid catfish and to a lesser extent channel catfish, typically results in a large variation in size at harvest, often ranging from 0.75 pounds to more than five pounds. Over- and under-sized fish are often heavily discounted by the processors or categorized as “weigh backs” of no value. Research conducted by ARS scientists in Stoneville, Mississippi, in collaboration with Mississippi State University scientists, have demonstrated grading fingerlings before stocking in a grow-out pond reduces food fish size variation. It has also been shown partial harvest or “topping off” food-size fish during the summer reduces the number of large fish in the fall, but also reduces the total net production.
While size variation in stocked fingerlings has been shown to have a great impact on food fish size variation, little research has yet been done on factors resulting in size variation in pond run fingerlings. ARS scientists at Stoneville, Mississippi, have begun preliminary study to determine the variation in fry size based on the age of the female brooder and also variation in fry size based on the age of swim-up fry when stocked. Ten pond spawns from each of two, three and four-year-old Delta Select (channel catfish) female brooders have been collected and incubated in the hatchery. Samples of sac fry, and two-, four-, and six-day-old swim-up fry will be collected to determine average wet- and dry-weights, and with-in spawn variation based on individual wet weights of 100 fry per spawn. Data are now being collected and analyzed. lf large variations in stocked fry size are found, future pond studies will be conducted to determine the impact of this on fingerling size variation. Farmers may be able to minimize the size range of fingerlings by stocking more uniform fry.
Numerous pond studies have demonstrated that dissolved oxygen concentrations below 3 mg/L in the morning result in lower feed intake, growth, and production in Channel, Blue, and hybrid Catfish. A laboratory project has begun to understand the physiological mechanisms that impact appetite/feed intake in Channel Catfish during periods of low dissolved oxygen (acute hypoxia). Several neuropeptides (brain proteins) are suspected to be involved in the control of appetite in catfish. This project has four components; development of the analytical techniques needed to measure neuropeptides and their gene expression; a broad sampling of neuropeptide(s) gene expression during hypoxia; measuring specific neuropeptide gene expression during varying durations of hypoxia; and determining the function of selected neuropeptides. We have developed a laboratory water handling system that allows us to control dissolved oxygen concentrations in tanks so we can perform the necessary experiments on groups of catfish. Additionally, we have developed analytical methods to measure gene expression of the neuropeptides of interest. Initial results have shown that only certain regions of the brain are involved in the response to hypoxia. We have collected tissue samples and are completing the broad sampling of genes expressed during hypoxia. We have completed individual gene measurements at different time points and have identified conditions that increase gene expression of neuropeptides. Additionally, certain blood parameters change dramatically as a result to exposure to hypoxic conditions. Besides providing a greater basic understanding of the responses of fish to environmental stressors, these studies may lead to a more efficient selection of fish based on the individual gene expression of critical neuropeptides rather than mass selection from long-term pond production studies.
Split ponds use screens to prevent the movement of fish between the two sections. The screens themselves restrict the water flow reducing efficiency to some extent, and collection of grass clippings, weeds and other debris on the screens restrict it further. Significant labor is required to clean the screens. Scientists at the University of Mississippi in Oxford, Mississippi, continued the investigation into the use of acoustic stimuli as deterrents to fish movement between the sections in split ponds. The propagation data was analyzed and appropriate sound levels were determined that should be audible by fish but not harmful. A hardware system was assembled and tested to generate a variety of sounds in a pond and monitor fish movement within a small area. This system will allow the researchers to play arbitrary sounds and determine how it affects fish movement near the screens separating the pond sides. The system will be tested in split ponds with fish to help determine the effectiveness of various sounds and signals as well as determine if the fish eventually acclimate to the acoustic stimuli.
Accomplishments
1. Development of management practices to minimize size variation in hybrid catfish food fish ponds. Two management practices to reduce food fish size variation and resulting weigh backs have been developed by ARS scientists at Stoneville, Mississippi, in collaboration with Mississippi State University scientists also at Stoneville, Mississippi. While in some cases mid-season partial harvest of larger fish can be used with an economic benefit, most farmer have adopted the use of graded fingerlings as has been recommended by Agricultural Research Service scientists when processors penalize farmers for out-of-size food fish.
2. Assessment of phytase “super-dosing” in catfish diets. ARS scientists at Stoneville, Mississippi, in collaboration with Mississippi State University scientists, conducted two experiments to evaluate responses of hybrid catfish, female Ictalurus punctatus × male Ictalurus furcatus, to “super-dosing” of 6-phytase added to existing commercial catfish feeds. It was shown that phytase super-dosing does not appear to have additional benefits beyond the standard dose, at least on promoting growth and preventing anemia in catfish, and also had no beneficial effects on water quality. Ongoing technology transfer efforts recommend 500 phytase units [FTU/kg] phytase and not “super-dosing” to replace inorganic phosphorus in catfish feeds.
3. Determination of dissolved oxygen requirements of separated hybrid catfish eggs incubated in vertical tubes. ARS scientists at Stoneville, Mississippi, had previously determined that channel catfish eggs, incubated as intact egg masses, require water with dissolved oxygen at over 95% air saturation during the last day of incubation for optimum development. Recent research by the same scientists determined that the maximum dissolved oxygen requirement for separated hybrid catfish eggs during the last days of incubation was only 79%. ARS scientists at Stoneville, Mississippi, have begun recommending that farmers maintain the dissolved oxygen in vertical tubes at or above 80% air saturation during the last two days of incubation to maximize egg development.
Review Publications
Boyd, C.E., Torrans, E.L., Tucker, C.S. 2018. Dissolved oxygen and aeration in ictalurid catfish aquaculture. Journal of the World Aquaculture Society. 49:7-70.
Boyd, C.E., Torrans, E.L., Tucker, C.S. 2018. Dissolved oxygen and aeration in ictalurid catfish aquaculture. Journal of the World Aquaculture Society. 49(1):7-70.
