Location: Warmwater Aquaculture Research Unit2020 Annual Report
Objective 1. Enhance selection of channel and blue catfish broodstock for economically important traits. Sub-objective 1.1. Continue selection for increased growth rate and carcass yield in channel catfish, blue catfish and channel catfish x blue catfish hybrids, and establish a selected line of blue catfish to produce improved broodstock. Sub-objective 1.2. Determine magnitude of genetic variation and evaluate potential for including additional traits in channel and blue catfish selection indices. Sub-objective 1.3. Characterize structural variation in the channel and blue catfish genomes and examine the potential for this information to improve the accuracy of estimated breeding values. Objective 2. Improve the efficiency of reproduction for purebred and hybrid catfish. Sub-objective 2.1. Identify and test reproductive pheromones in channel and blue catfish. Sub-objective 2.2. Evaluate the formulation of mammalian Luteinizing Hormone Releasing Hormone analog to improve ovulation and hatching success to improve the efficiency of hybrid catfish embryo production. Sub-objective 2.3. Determine impact of broodfish nutritional strategies on maturation and reproductive performance of channel catfish to maximize hatching success and hybrid catfish fry production. Objective 3. Increase efficiency of warmwater aquaculture by developing and improving production systems and management practices. Sub-objective 3.1. Model split-pond ecosystem dynamics to optimize design and performance. Objective 4. Improve catfish product quality by identifying and managing pre-harvest factors that affect the quality of catfish products. Sub-objective 4.1. Isolate and identify geosmin-producing species of cyanobacteria from catfish aquaculture ponds and determine the seasonal occurrences of blooms of these noxious cyanobacteria species. Sub-objective 4.2. Determine the efficacy of using sodium carbonate peroxyhydrate (SCP) in managing undesirable blooms of cyanobacteria in west Mississippi catfish ponds. Sub-objective 4.3. Determine the effects of pond culture systems on fillet flavor and texture of hybrid catfish.
In order to enhance selection of channel and blue catfish broodstock for economically important traits we will continue selection for increased growth rate and carcass yield in channel catfish, blue catfish, and channel x blue catfish hybrids, and establish a selected line of blue catfish to produce improved broodstock; determine the magnitude of genetic variation and evaluate potential for including additional traits in channel and blue catfish selection indices; and characterize structural variation in the channel and blue catfish genomes and examine its potential to improve the accuracy of estimated breeding values. In order to improve catfish reproductive efficiency, we will identify reproductive pheromones of channel and blue catfish; evaluate the formulation of mammalian Luteinizing Hormone Releasing Hormone analog to improve ovulation and hatching success to improve the efficiency of hybrid catfish embryo production; and determine the impact of broodfish nutritional strategies on maturation and reproductive performance of channel catfish to maximize hatching success and hybrid catfish fry production. In order to increase the efficiency of warmwater aquaculture by developing and improving production systems and management practices, we will model split-pond ecosystem dynamics to optimize system design and performance. In order to improve catfish product quality by identifying and managing pre-harvest factors that affect the quality of catfish products, we will isolate and identify geosmin-producing species of cyanobacteria from catfish aquaculture ponds and determine the seasonal occurrences and blooms of these noxious cyanobacteria species; determine the efficacy of using sodium carbonate peroxyhydrate (SCP) in managing undesirable blooms of cyanobacteria in west Mississippi catfish ponds; and determine the effects of pond culture system on fillet flavor and texture of hybrid catfish.
The release of channel catfish and blue catfish germplasm to U.S. catfish producers was the most significant event in this reporting cycle. The release was advertised in The Catfish Journal, an industry publication, and most fingerling producers participated in the release. This was the first release of the Delta Select channel catfish population that demonstrated improved growth and carcass yield. It was also the first germplasm release of blue catfish, which constitute the paternal line in the F1 hybrid cross. Approximately 60-70% of catfish raised in the US are hybrids, so the blue catfish germplasm was readily received by hybrid producers. The 2020 spawning season saw the initial commercial use of the catfish gonadotropin release hormone II analog (GnRH IIa) that was developed at the Warmwater Aquaculture Research Unit. Personal communications with hatchery managers revealed the spawning aid was successful compared with previously used mammalian-based gonadotropins and managers planned to increase their use of catfish GnRH IIa next spawning season. Warmwater Aquaculture Research Unit scientists published the most extensive (85 pages) peer-reviewed manuscript that reviewed decades of off-flavor research in pond-raised catfish. The value of this manuscript lies in its description of the complexity of the off-flavor issue, and presentation of many approaches to ameliorating off-flavor, most of which have not worked. Research was conducted to determine whether varying phosphorus concentrations in fish feed affected the bloom of blue-green algae in earthen ponds and thereby affected the incidence of off-flavor from geosmin and 2-methylisoborneol produced by the cyanobacteria and bioaccumulated in the fish flesh. The fish were fed for six months, and water and fish samples were collected to measure levels of the two off-flavor compounds. Covid19 restrictions hindered laboratory research progress and efforts of the limited number of staff were focused on maintaining animal care and welfare. Field research aimed toward off-flavor research in industry ponds was hindered due to covid-based travel limitations. WARU successfully produced the next generations of Delta Select channel catfish and Rio Grande and Delta Elite blue catfish. The retirement or resignation of three scientists, the Facility Manager, the Program Support Assistant, and the Information Technology Specialist also constrained research progress, and recruitment efforts are underway to refill vacancies.
1. Development and release of the Delta Select strain of channel catfish. Mission includes development of improved catfish germplasm for release to U.S. catfish farmers. Use of improved catfish germplasm will allow U.S. catfish farmers to reduce production costs and remain competitive in the global seafood market. ARS researchers initiated and continue a selective breeding program to develop a strain of channel catfish (referred to as the Delta Select strain) with superior growth rate and meat yield, traits important to catfish producers and processors. After conducting trials demonstrating improved growth and carcass yield of the Delta Select strain compared to other strains of channel catfish a release of the Delta Select strain channel catfish to U.S. catfish farmers was completed in March of 2020. Approximately 90,000 head (180,000 pounds) of 2-year-old Delta Select strain catfish were released to 12 of the 15 commercial catfish hatcheries in the U.S. with significant channel catfish production. The release provides U.S. farmers access to improved catfish germplasm and will make U.S. catfish farmers more efficient and profitable.
2. Evaluation, development and release of blue catfish germplasm. Over the last 15 years, U.S. catfish production has shifted from predominant use of purebred channel catfish to the current situation where F1 hybrids between channel catfish and blue catfish accounts for over 60% of production. Therefore, evaluation and development of improved blue catfish germplasm has become an important part of the mission to develop improved catfish germplasm for release to U.S. catfish farmers. ARS researchers in Stoneville, Mississippi, evaluated seven strains of blue catfish and found that the Rio Grande strain produced both purebred and hybrid catfish progeny with superior growth and meat yield relative to other blue catfish strains. ARS reseachers initiated the development of a composite strain of blue catfish, referred to as the Delta Elite strain, by crossing blue catfish from the four best performing strains of blue catfish from the seven strains evaluated at WARU. This composite strain possesses increased genetic variation and will be selected for improved performance along with the Rio Grande Strain. In April of 2020, 60,000 pounds (30,000 head) of Rio Grande and Delta Elite blue catfish were released to seven of the nine commercial hatcheries producing hybrid catfish, providing U.S. catfish farmers with unique and improved blue catfish germplasm.
3. Effects of catfish diets and feeding strategies on meat yield. Meat yield, the percentage of whole fish weight comprised on saleable meat, is an important trait in farm-raised catfish and diet composition and feeding regimes can affect meat yield. Catfish farmers are sometimes unable to sell market weight catfish for processing due to lack of demand in the supply chain causing issues with production management. If the fish are fed during this time, they grow larger than the preferred size for processing and the price paid to farmers is reduced substantially. If the fish are not fed, they mobilize muscle tissue for energy and fillet yield is decreased and the price paid to farmers is reduced. ARS researchers in Stoneville, Mississippi, worked in cooperation with Mississippi State University (MSU) fish nutritionists to determine that hybrid catfish fed once or twice weekly for four months remained in the preferred size for processing but had decreased fillet yield. Thirty days of full feeding were needed to restore fillet yield to normal levels in fish were fed once or twice weekly for four months. Results from these studies are provided to catfish producers and processors and allow the catfish farming industry to develop feeding strategies to minimize production costs and maximize profits.
4. Release of the GnRH IIa spawning aid to farmers. ARS researchers in Stoneville, Mississippi, have demonstrated the advantages of using a synthetic peptide analog of catfish gonadotropin releasing hormone II (GnRH IIa) compared to a mammalian luteinizing hormone releasing hormone analog for stimulating the final maturation and release of eggs for manual spawning. ARS researchers in Stoneville, Mississippi, developed a Non-funded Cooperative Agreement with DelTaq Fish Health Services in Stoneville, Mississippi, to obtain an Investigational New Animal Drug (INAD) from the U.S. Food and Drug Administration. The new spawning aid became available for purchase in early 2020 and quantities purchased by US producers were estimated to supply half the industry’s need for hybrid catfish production during the 2020 spawning season. The success of the new spawning aid in 2020 suggests an increased demand for the peptide in 2021.
5. Production of pyranopyrans as potential bacteriocidal compounds against fish pathogens. Loss of commercially raised catfish to disease can result in annual economic losses up to $100 million, and reduction or elimination of bacterial pathogens is critical to the improvement of catfish health. In order to identify novel antibacterial compounds useful against fish pathogens, ARS researchers in Oxford, Mississippi, and in Stoneville, Mississippi, and Villanova University modified the chemical structures of natural compounds produced by a species of fungus to produce novel compounds. The novel compounds, pyranopyrans, possessed significant antibacterial activities against certain species of fish pathogenic bacteria. The scientists received a U.S. Patent for the production and use of these compounds. The limitations of currently approved therapeutants and the adversity to the use of antibiotic-laden feeds in agriculture make acceptance of alternative efficacious natural or natural-based compounds that are active against common fish pathogenic bacteria very acceptable to the catfish industry, with a high percentage (> 50%) of producers expected to utilize the invention. These novel compounds may be useful in mitigating the detrimental effects of common bacterial fish diseases and reduce the economic costs of these diseases which can result in losses of $100 million (U.S.) annually.
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