Aquaculture (NP 106) Annual Report for 2011

Vision: The vision for ARS aquaculture research and technology transfer is to support a 

thriving domestic industry based on improved systems developed through research and 

application of better genetic stocks, improved diets and nutrition, enhanced aquatic animal 

health, and consistent water quality. Our program supplies scientific information on

processes, biotechnologies, and management practices to ensure a high quality, safe supply 

of healthful seafood and aquatic products.

Mission: The mission of the Aquaculture National Program is to conduct high quality, 

relevant, fundamental and applied aquaculture research, to improve the systems for raising

domesticated aquaculture species, and to transfer technology to enhance the productivity and 

efficiency of U.S. producers and the quality of seafood and other aquatic animal products.

The primary aim of the ARS Aquaculture Program, as described in the National Program 106 

Action Plan, is to help develop and ensure an abundant, safe, and affordable supply of 

seafood products within a healthy, competitive, and sustainable aquaculture sector. This

sector is supported by over 4,300 aquaculture farmers who produced in excess of $1 billion 

dollars worth of goods in 2005 (NASS, 2005 Census of Aquaculture). 

Over the past year, there has been striking success in many of our projects, including 

germplasm development and release to industry of Atlantic salmon, oysters, and rainbow 

trout; patenting of new vaccines to prevent warmwater fish diseases caused by Streptococcus 

iniae and columnaris; and several improved technologies to improve profitability in the 

farmed catfish industry. 

NP 106 Events in 2011

We welcomed Travis Brown, Ph.D. as a post-doc with the Catfish Genetics Research Unit in 

Stoneville, Mississippi.

There were no new scientist positions filled in the Aquaculture National Program during the 

2011 fiscal year; however, several scientists have retired in early 2012: Ken Davis from the 

Catfish Genetics Research Unit in Stoneville, Mississippi; Julie Bebak-Williams from the 

Aquatic Animal Health Research Unit in Auburn, Alabama; and Don Freeman from the 

Stuttgart National Aquaculture Research Center in Stuttgart, Arkansas. Don has had a long 

and distinguished career with ARS, heading up the original ARS aquaculture programs in the 

early 1980’s in the Mid-South Area.

Awards and Recognitions:

Scientists in the Aquaculture National Program were well recognized nationally and 

internationally over the past year, with many invited presentations. The following scientists 

in the Aquaculture National Program were recognized with prominent awards:
Julia Pridgeon, Aquatic Animal Health Research Unit, Auburn, Alabama

(Early Career Scientist Award, Mid-South Area)

Phil Kleisus, Craig Shoemaker, and Joyce Evans, Aquatic Animal Health Research 

Unit, Auburn, Alabama (2011 Honorable Mention for Technology Transfer, National

Federal Laboratory Consortium for tilapia diseases, immunology, and vaccines)

National Program 106 involves efforts in nine units at 13 different locations on 23 projects

performed by nearly 100 scientists (49 ARS scientists and an equal number of collaborating 

scientists). Technology transfer activities included invention disclosures, patent filings,

Cooperative Research and Development Agreements (CRADA), and Material Transfer 

Agreements (MTA). These agreements cover transfer of Atlantic salmon germplasm to 

commercial producers, supplies of rainbow trout families to university, industry, and State 

hatchery collaborators, development of vaccines and vaccination methodologies, and transfer 

of specific pathogens strains for vaccine work. A number of additional activities to transfer 

technologies to other scientists and to industry partners were also completed. Among the

outstanding examples of success is the ongoing effort to improve hybrid catfish production at 

Stoneville, Mississippi, where scientists are working closely with a number of hatchery 

operators in the Mississippi Delta region and having tremendous success increasing the 

number of hybrid fry produced across the industry. Another example is the rapid 

development of numerous fish diets including new ingredients. The Trout Grains Project has 

worked with multiple collaborators to improve, develop, and test new ingredients, leading to 

new feed formulations and opportunities for ingredient manufacturers.

Across the program, researchers maintained beneficial collaborations with a number of 

international investigators and laboratories. Canada and Norway lead the list in terms of the 

active collaborations. Work ranges across cooperation on salmon breeding efforts and 

information-sharing on recirculating aquaculture systems with Canadian counterparts, to 

exchange with the Norwegian Aquaculture Protein Center on feed processing, and with the 

Norwegian Institute of Food, Fisheries and Aquaculture Research (NOFIMA) on fish health 

and well-being in recirculation systems. Our aim is to form real partnerships that have benefit 

to the United States and to cooperating countries. These relationships increase the depth of 

our intellectual capital with original ideas from different perspectives.

Funding: During fiscal year 2011, total funding for Aquaculture research was 

approximately $32,164,200. Additional funds have come from grants, other government 

agencies, and industry. The National Center for Cool and Cold Water Aquaculture (Leetown, 

West Virginia), Trout-Grains project (Hagerman, Idaho), Catfish Genetics Research Unit 

(Stoneville, Mississippi), Aquatic Animal Health Research Unit (Auburn, Alabama), and the 

National Cold Water Marine Aquaculture Center all received extramural funds.

Research Results

The following section of the report summarizes the specific high impact research results 

addressing objectives in the current National Program Action Plan.
Genetic and Genomic Resources:

Faster growing Atlantic salmon developed and germplasm released to commercial 

producers

Increasing harvest size and reducing the time to harvest of Atlantic salmon are two goals of 

the salmon producers in North America. Commercial salmon producers in the United States

utilize stocks that are not many generations removed from wild, unselected stocks and are 

legally required to culture stocks certified to be of North American origin. ARS researchers 

at the National Cold Water Marine Aquaculture Center in Franklin, Maine, evaluated the 

growth of salmon from their breeding program in commercial sea cages in collaboration with 

industry. A salmon line selected for faster growth and greater weight was produced and 

germplasm was released to commercial producers. Utilization of improved germplasm will 

reduce the time to harvest, increase the profitability and sustainability of coldwater marine 

aquaculture in the United States, and provide a quality seafood product to U.S. consumers.

Rapid, reliable production of sterile, fast growing salmonids 

Production of sterile (non-reproductive) salmonids is important in situations where 

reproductive interaction with natural populations is undesirable. For example, where trout 

will be released for sport-fishing in regions that support natural (but not numerous) 

populations and genetic interaction would be detrimental. Current methods used to create 

sterile rainbow trout involve manipulating sets of chromosomes during early embryonic 

development. Most techniques are less than 100% effective, therefore benefits of sterility 

(e.g., more efficient growth and reproductive isolation) are not fully realized and resources 

must be used to screen for sterile individuals. ARS researchers in Leetown, West Virginia,

identified that correcting for egg age post-ovulation improves timing of chromosome set 

manipulation. Methods developed allow sampling of very few fish to determine parameters 

for efficiently manipulating chromosomes for entire spawning groups. As a result, sterile 

salmonids can be produced with more certainty and less effort required to validate sterility.

Third generation of selectively bred yellow perch has been developed

In Spring 2010, select performers of the second generation for each of three strains of perch 

(Perquimans, Choptank, Winnebago) were developmentally accelerated through 

environmental manipulation and spawned in 2011 to produce third generation growthselected progeny for each strain. Selection for growth has decreased the time to market size 

(between the first and second generations) by 1.5 months (about 15%) and further gains are 

expected in subsequent generations.

Release of novel Kumamoto oyster breeding stock, Ariake Kumo

Existing U.S. Kumamoto oyster breeding stock had been hybridized with Pacific oysters and 

subjected to excessive inbreeding, producing undesirable characteristics and making larval 
culture difficult. In 2006, ARS researchers at Newport Oregon, in collaboration with the

Molluscan Broodstock Program at Oregon State University, the University of Southern 

California, and Taylor Shellfish Farms collected a genetically diverse sample of Kumamoto 

oysters from the Ariake Sea in southern Japan and used molecular markers to confirm their 

species identification. From 2007-2010, an entire generation was raised under strict 

quarantine conditions. Extensive disease testing was conducted on the imported parents and 

their first- and second-generation progeny to preclude the introduction of non-native pests 

and pathogens. This non-inbred and non-contaminated breeding stock is currently being used 

and evaluated by commercial producers and is likely to replace or revitalize current stocks 

and thus enhance the production of Kumamoto oysters.

Estimation of genetic parameters for growth and Enteric Septicemia of Catfish (ESC)

resistance in channel catfish

Information on heritabilities and interactions among economically important traits is required 

for efficient improvement of these traits in channel catfish. ARS scientists located at the 

Catfish Genetics Research Unit in Stoneville, Mississippi, evaluated channel catfish growth, 

fillet yield, and resistance to ESC as part of an integrated breeding program. Heritability for 

growth and fillet yield were moderately high (0.35 and 0.38, respectively) while heritability 

for survival to ESC challenge was not different from zero. Breeding values were estimated 

and fish were selected for improved growth and fillet yield based on a selection index with 

equal weighting for growth and fillet yield. The selected catfish form the foundation for a 

genetically improved population intended for release to the industry.

ARS trout lines incorporated into commercial lines

Plant-based fish feed reduces dependence on marine fishery resources. ARS researchers in 

Hagerman, Idaho, have selected lines of rainbow trout for several generations for improved 

feed conversion, protein retention, and growth rate at six months after first feeding when fed 

fish-meal free, barley-containing diets. Working jointly with a commercial partner, these 

trout were incorporated into a commercial breeding program. During the next production 

cycle these fish will account for at least 15% of commercially produced rainbow trout in the 

United States. Improved genetic trout lines from the ARS broodstock program are available 

to the trout industry and to trout researchers nationwide.

Animal Performance, Well-being and Efficiency:

Supplementing lipid in catfish diets improves sexual maturity and reproductive

performance of channel catfish 

Hybrid catfish (a cross between a female channel catfish and a male blue catfish) production 

requires the strip spawning of a huge quantity of high quality eggs. Lipids and fatty acids 

play a major role in broodstock nutrition and influence the quality of developing eggs. Pond 

trials conducted by ARS scientists at the Catfish Genetics Research Unit in Stoneville, 
Mississippi, showed that catfish oil incorporated as a dietary lipid supplement improved the 

fatty acid content of eggs and subsequent reproductive performance of channel catfish. With 

a 5% catfish oil supplementation to the diet compared to 2% in the control diet, a higher 

percent of catfish females reached maturity (78% vs. 60%), they produced 20% more eggs, 

with a 16% increase in hatch rate of the hybrids, all leading to superior hybrid catfish 

production. 

Regulators of feed efficiency in catfish

Factors that control feed efficiency are not well understood in catfish. Therefore ARS 

scientists in Stoneville, Mississippi, conducted research to investigate the role of 

mitochondrial respiratory chain enzyme activities on low and high Feed Efficient (FE) 

families of catfish. Mitochondrial complex enzyme activities showed that the activities of the 

liver mitochondrial complexes (I, II, III, IV) were all lower in the low FE family compared to 

the high FE family. Enzyme activities of the muscle and gene expression from the liver and 

muscle are currently being evaluated. Understanding how the mitochondrial respiratory chain 

controls FE will help researchers develop strategies to improve FE in catfish.

Efficacy of salmon luteinizing hormone releasing hormone (LHRHa) to induce channel 

catfish spawning for hybrid embryo production

Exogenous hormone treatments are successfully used in channel x blue hybrid embryo 

production in catfish hatcheries but there is a need for an effective hormone that can be 

applied at reduced rates to lower production costs. ARS scientists at the Catfish Genetics 

Research Unit in Stoneville, Mississippi, demonstrated that low doses of salmon LHRHa 

were as efficacious as the currently used mammalian LHRHa to induce channel catfish 

ovulation. The results of this research were field tested in three commercial hatcheries. Low 

dosage salmon LHRHa can reduce the hormone costs associated with strip spawning of 

channel catfish in hybrid embryo production.

Nutrient Requirements, Nutrient Composition of Feedstuffs, and Expanding 

Alternative Ingredients 

Development of a standardized digestibility database for traditional and alternative feed 

ingredients 

To develop new ingredients for fish feed diets, the availability of the nutrients in the 

ingredients, known as digestibility, need to be determined. This information must be 

generated empirically by testing the ingredients on fish, there are no laboratory methods with 

commercial processing to determine digestibility. ARS scientists in Hagerman, Idaho, and 

Stuttgart, Arkansas, compiled a first of its kind database containing digestibility coefficients 

for macro-nutrient, amino acids, and minerals for 80 ingredients with rainbow trout and 26 

ingredients with hybrid bass. This information has been requested by commercial aquafeed 
companies and ingredient suppliers both nationally and internationally, and will allow for 

more efficient feed utilization and ingredient substitution by the aquaculture industry.

Wheat distiller's dried grains with solubles (WDDGS) is an economical feed alternative in 

aquaculture

Feed cost is the single largest expenditure in intensive fish production and protein is the most 

expensive component in fish feeds. For the aquaculture industry to be profitable and 

sustainable, feed costs must be reduced. Distiller's dried grains with solubles (DDGS), the 

main byproduct of the ethanol industry, are readily available at a lower cost than most 

commonly used protein sources but their use in fish feeds is limited because of the high fiber 

content. Wheat DDGS differs markedly in nutrient content from corn DDGS. No information 

is available on its use in fish diets. ARS scientists located at the Aquatic Animal Health 

Research Unit in Auburn, Alabama, evaluated the influence of dietary levels of WDDGS on 

growth performance and feed utilization efficiency in tilapia and catfish. Results of this 

research showed that 30% and 20% WDDGS can be used in tilapia and catfish feeds, 

respectively, as replacement, on an equal protein basis, for a mixture of soybean meal (SBM) 

and corn meal (CM) without requiring the addition of lysine. With supplementation of lysine, 

WDDGS level can be increased to 40% for both species. Replacement of a mixture of SBM 

and CM in catfish feed with 20% WDDGS and in tilapia feed with 30% WDDGS or 40% 

WDDGS with added lysine (for both species) reduced feed cost by at least $15/ton. 

Moreover, incorporation of DDGS in fish diets will also lead to increase in demand and 

expand the market of the U.S. DDGS.

Alternative feeding ingredients

Prices of soybean meal and corn, the two most commonly used traditional feed ingredients in 

channel catfish diets, have increased dramatically in recent years. Using less-expensive 

alternative feed ingredients to partially replace soybean meal and corn will reduce feed cost. 

ARS scientists at the National Warmwater Aquaculture Center, Stoneville, Mississippi, 

investigated the use of corn gluten feed and cottonseed meal, two promising alternative 

feedstuffs, as replacements for soybean meal and corn in diets for pond-raised channel 

catfish. The study showed that a maximum of 50% of the soybean meal in channel catfish 

diets may be replaced (soybean meal was reduced from 51.4% to 25.7%) by a combination of 

corn gluten feed and cottonseed meal (up to 20% of each in the diet) without markedly 

affecting the physical quality of feed pellets, fish growth, processed yield, and body 

composition. Results are being used by catfish feed mills to reduce feed costs while 

providing a nutritionally complete feed for commercial catfish farming.

Developed sustainable commercial feeds for Atlantic salmon

Sustainable aquafeeds for Atlantic salmon (Salmo salar) are being developed using 

alternative protein blends in collaboration with the University of Idaho on a marine 
aquaculture research grant funded by the National Oceanic and Atmospheric Administration. 

Two alternative soybean and wheat protein sources were evaluated to replace expensive 

animal proteins in juvenile Atlantic salmon diets by scientists at the National Cold Water 

Marine Aquaculture Center in Franklin, Maine. Juvenile Atlantic salmon had similar growth 

and feed conversion ratios compared to salmon fed a typical fish meal feed demonstrating 

that plant based proteins can cost-effectively replace animal proteins in salmon diets. Data 

from these trials have been requested by a commercial feed company for consideration of 

these ingredients in commercial salmon diets.

Improving Health 

Novel diagnostic assays differentiate virulent strains of the fish pathogen, Yersinia ruckeri

The fish disease “enteric redmouth” caused by the pathogen Yersinia ruckeri was a 

devastating disease that has been controlled for years with an effective vaccine. However, 

recently newly identified strains of Y. ruckeri, called Y.ruckeri biotype 2 (BT2), pose an 

emerging threat to rainbow trout aquaculture and improved diagnostic assays are needed. 

ARS researchers at the National Center for Cool and Cold Water Aquaculture located in 

Kearneysville, West Virginia, have developed assays for the rapid and precise identification 

of the three specific strains of BT2 Y. ruckeri that are currently circulating in the United 

States and Europe. The assays are easy to perform and interpret and depend on equipment 

already common to diagnostic laboratories. These assays will be used to identify infected fish 

populations, and will facilitate the application of specific vaccines or other management 

practices aimed at controlling these newly emerging strains of bacteria in aquaculture.

Vaccine developed to protect fish against columnaris disease

Flavobacterium (F.) columnare is the causative agent of columnaris disease. Columnaris 

disease is threatening both warm water and cold water fish worldwide. Annually, columnaris 

disease is responsible for economic losses of at least $30 million to fish farmers. To control 

bacterial diseases, use of antibiotics is a general method. However, antibiotics are too 

expensive. In addition, frequent use of antibiotics has led to the development of antibioticresistance in the fish pathogen. Therefore, alternative methods to control bacterial diseases 

are urgently needed. ARS scientists at Auburn, Alabama, developed an attenuated live 

vaccine against columnaris disease, which offered significant protection for both channel 

catfish and largemouth bass. This vaccine has been commercially licensed to prevent 

columnaris disease, benefitting fish farmers and the aquaculture industry.

Progress to combat proliferative gill disease (PGD) in catfish

Proliferative gill disease (PGD) or hamburger gill, is the most prevalent and costly parasitic 

disease associated with the commercial production of channel catfish. Infection by the 

parasite can result in a severe inflammatory response at the gills with mortality rates 

approaching 100% in severe outbreaks. Recently, a rapid quantitative molecular assay has 
been validated for the detection and quantification of infectivity levels in pond water that can 

predict production losses in newly stocked fish. For control measures, the anti-parasitic drug 

amprolium was shown to reduce parasite levels in the fish host 60 days post-infection. 

Further, smallmouth buffalo, a fish which feeds on bottom dwelling worms that are part of 

the parasitic lifecycle, reduce infections in fish. Predictability and control strategies are 

helping to reduce losses to PGD.

Antiviral pathway identified in fish cells 

Various fish cell lines have been developed to characterize viral recognition and response 

pathways in fish. ARS collaborators have individually expressed the major proteins of the 

viral hemorrhagic septicemia virus (VHSv) in fish cells to investigate infectivity and 

virulence of these proteins at a cellular level. Two VHSv proteins were found to inhibit 

antiviral responses in fish cells, decreasing production of the antiviral molecule, interferon. 

Furthermore the research indicated that interferon already present in the cell can block VHSv 

from multiplying. Collectively, this work suggests that the VHS virus adversely affects the 

cellular response to interferon which allows virus replication. Knowledge of how particular 

VHSv proteins affect the viral recognition and response pathway in fish will enable 

development of a more targeted and effective vaccine for treatment of this pathogen in 

important aquaculture species.

Determining the role of macrophages in resistance and susceptibility to disease in catfish

Developing strategies for improving disease resistance through selective breeding requires an 

understanding of the biological and genetic basis of resistance to disease. ARS scientists at 

the Catfish Genetics Research Unit in Stoneville, Mississippi, have cultured macrophages 

from catfish that demonstrate a highly resistant (>80% survival) or a highly susceptible 

phenotype, following experimental challenge with relevant pathogens. Results of 

experiments show that macrophages from resistant families have an enhanced ability to kill 

intracellular pathogens and are able to inhibit intracellular replication, despite the fact that 

there is no difference in initial uptake rates of pathogens by either “resistant” or “susceptible”

cells. The results from these studies will be confirmed and extended with the intention to 

improve vaccine development and selective breeding to enhance innate immunity in catfish.

Production Systems and Products:

Dramatic production improvements through pond oxygen management

Dissolved oxygen is 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, examined the impact of pond 

dissolved oxygen (DO) concentrations on catfish growth, yield, food consumption, and food 

conversion. A computer-controlled pond oxygen monitoring system maintained precise DO 

set-points. Results showed that for optimum food conversion and growth, DO levels of 2.5 to 
3.0 mg/L are required and this is higher than common practice for the industry. With higher 

levels of DO, improved growth will significantly shorten the production cycle and reduce 

fish losses to all causes, significantly improving food conversion. Increased growth resulting 

from improved DO management can reduce food conversion ratios (weight of feed input/fish 

weight gain) from an estimated industry-wide 2.5-3 to 2, reducing production costs by $0.10-

0.20/lb, greatly improving the profitability of catfish farming.

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 dissolved oxygen (DO) 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 the standard oxygen transfer rate (SOTR) and standard aeration 

efficiency (SAE). 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.

A split-pond aquaculture system

A split-pond aquaculture system has been developed that potentially can increase channel 

catfish production by 2 or 3 times that achieved in traditional earthen ponds. The new system 

splits an existing earthen pond into two unequal sections with an earthen levee and then links 

the two systems by circulating water that is pumped with a large, efficient, slow-turning 

paddlewheel. Fish are held in the small section and the larger section provides waste 

treatment and oxygen production. The new, full-size (4.5-acre) system studied by ARS 

scientists at the National Warmwater Aquaculture Center in Stoneville, Mississippi, produced 

77,000 pounds of fish (17,000 pounds/acre) at a feed conversion ratio of 1.8. Based on these 

results, several hundred acres of split-ponds have been built by commercial farmers in 

Mississippi and Arkansas.

New analytical method developed for measuring the degree of starch gelatinization

Starch gelatinization plays an important role in determining the structural and textural 

properties of processed foods and feeds. It also affects human and animal nutrition through 

changing enzymatic access to glucosidic linkages and the consequent digestibility of starch. 

Several methods are available to measure the degree of starch gelatinization, but some of 

them require costly instrumentations while others are applicable only to purified starch. ARS 

researchers at Aberdeen, Idaho, have developed a new rapid and low cost enzymatic method 
that can measure the degree of starch gelatinization, not only for purified starch, but also for 

processed feed or food. This new method will speed development of new feeds.

Maximizing Atlantic salmon health and performance in recirculating aquaculture systems

A major cost of raising fish in closed, recirculating systems is pumping and treatment of 

water in the culture system. To keep the pumping and treatment costs at the minimum 

possible, safe water quality criteria must be well-defined. Elevated carbon dioxide (CO2) can 

negatively affect fish performance and is a key water quality parameter that has traditionally 

been maintained at or below 10 mg/L. Scientists at The Conservation Fund Freshwater 

Institute in Shepherdstown, West Virginia, raised Atlantic salmon for 12 months at either 

high (20 mg/L) or low (10 mg/L) CO2 concentrations, and observed that performance and 

survival were comparable between treatments. Atlantic salmon can therefore be raised safely 

to market size at relatively higher concentrations of CO2. This means that water pumping 

can be reduced significantly and improve the cost effectiveness of closed containment fish 

production.

Swimming speed and dissolved oxygen (DO) concentration affect Atlantic salmon 

performance

Exercise has been shown to enhance salmonid performance, but DO levels can be limiting. 

Hence, there is a need for research optimizing swimming speed and DO parameters. 

Scientists at The Conservation Fund Freshwater Institute in Shepherdstown, West Virginia, 

determined that for Atlantic salmon mean weight was significantly enhanced by both higher 

DO levels and swimming speeds. Exercise significantly reduced the prevalence of precocious 

males, which have negative impacts on production. Increased performance and reduced 

precocity in industry can therefore be achieved through exercise and supplemental DO.

Alternative recirculating aquaculture system outperforms traditional recirculating system

Although recirculating aquaculture technologies allow for intensive fish production, 

increased biosecurity, reduction in water use and effluent discharge, these traditional systems 

are expensive to operate and are capital and energy intensive. Therefore, improvements in 

cost and energy efficiencies are needed to maximize profits per unit of volume. ARS 

researchers in Fort Pierce, Florida, in collaboration with Florida Atlantic University, 

demonstrated greater production and economic efficiencies using a low-energy, low-pressure 

recirculating system in a direct side-by-side comparison with traditional recirculating systems 

for the production of market-ready Florida pompano in low-salinity environments. While

nearly doubling the number of pompano produced per unit volume, and also establishing 

lower cost and greater efficiency, this technology provides marine fish producers an option 

that can be readily implemented.
Identification of the cause of earthy-musty off-flavors in recirculating aquaculture system 

(RAS)-cultured fish

Aquaculture systems that treat and recycle water can be extremely efficient with regards to 

water use. Nevertheless, off-flavors described as “earthy-musty” can be present in fish 

produced in recirculating aquaculture systems and such off-flavors could hamper growth of 

this industry. An ARS researcher at University of Mississippi, determined the compounds 

and microorganisms responsible for earthy-musty off-flavors in fish including arctic charr, 

barramundi, rainbow trout, and Atlantic salmon cultured in recirculating aquaculture 

systems. Discovery of the responsible compounds and determination of their concentrations 

in fish flesh have allowed the development of management practices that reduce the levels of 

the off-flavor compounds and provide a good-tasting, high-quality product to consumers. 

These management practices reduce off-flavor occurrence and thereby avoid economic losses 

due to delaying harvests, such as additional feeding costs, losses of fish to disease, and water 

quality problems. 

Commercial production of channel x blue hybrid catfish fry

Production of channel catfish x blue catfish hybrids has increased substantially over the last 

three years. Hybrids comprised about 20% of food fish harvested in 2011 and interest in 

producing hybrids continues to increase. The hybrid generally has better growth, survival,

and meat yield than channel catfish, which most producers currently grow. However, 

production of hybrid fry involves hormone-induced ovulation and manual (or strip) spawning 

of females. Few farmers are familiar with the techniques for hormone induced spawning 

required to produce hybrids. ARS scientists at the Catfish Genetics Research Unit (CGRU) in 

Stoneville, Mississippi, in conjunction with Mississippi State University scientists, offered a 

two day workshop demonstrating techniques for production of hybrid catfish fry. Eighteen 

catfish producers attended the workshop and provided very positive feedback. Additionally, 

CGRU scientists provided frequent on-site consultation to the six hatcheries that currently 

produce hybrid catfish fry. Hybrid fry production for the spring of 2011 was estimated to be 

110 million, an increase of 20% from 2010. Three additional hatcheries have contacted unit 

scientists indicating intent to produce hybrid fry in 2012 and requesting advice and assistance 

of unit scientists.

Effects of stocking density on production traits of channel catfish x blue catfish hybrid 

foodfish

Hybrid catfish are commonly grown in commercial ponds but more information is needed to 

determine best production strategies such as optimal stocking densities. ARS scientists at the 

Catfish Genetics Research Unit in Stoneville, Mississippi, performed pond growth trials of 

hybrid catfish fingerlines at varying stocking densities, then measured growth, survival, feed 

conversion, and meat yield. Net production (pounds of fish produced per acre) increased as 

stocking density increased but stocking density did not affect survival, feed conversion ratio, 
or meat yield from 3,000 to 9,000 fish per acre. However, ponds stocked at 11,000 fish per 

acre resulted in smaller fish and fewer fish of marketable size; therefore, the production cycle 

would be longer and production costs would increase at this density. The experiments 

provided key information on stocking parameters for hybrid catfish production.

Chrondroitin sulfate from fish

Chondroitin sulfate is taken orally by many individuals to help alleviate pain from arthritic 

joints, thus there is potential to increase the value of fish processing byproducts by extracting 

chondroitin sulfate from fish connective tissues. Therefore, a study was conducted by ARS 

scientists in Kodiak, Alaska, to determine chondroitin sulfate content in the different tissues 

of different salmon heads. Analytical techniques were adapted to determine chondroitin 

sulfate content in the heads of different salmon species and in fractions from red salmon 

heads. The fraction of the red salmon head that contains the highest concentration of 

chondroitin sulfate was the connective-tissue rich snout and braincase, or if from male 

salmon, the exaggerated kype (a pronounced curvature of the jaws in male salmon), with 34 

mg/g total chondroitin sulfate (dry weight basis). The levels of chondroitin sulfate in salmon 

heads appear to be sufficient to be used for the cost-effective extraction of chondroitin sulfate 

suggesting that extraction of chondroitin sulfate from fisheries byproducts is possible and 

may result in new value-added products.

Purification of salmon fish oil using a pilot scale adsorption column

An economically viable purification method is needed to remove impurities from unpurified 

salmon oil (USO) without changing the desirable fatty acid composition. A study by 

scientists at Louisiana State University in collaboration with ARS and University of Alaska 

scientists in Kodiak, Alaska, was initiated to develop an adsorption column process for 

purifying salmon oil. USO and purified salmon oil samples were analyzed for fatty acid 

profiles, peroxide values, free fatty acids, moisture content and rheological properties. This 

study demonstrated that the column adsorption process effectively reduced peroxide values, 

free fatty acids, and moisture content of salmon oil, which will improve the purification 

process for industry.