ARS Aquaculture National Program (106)

National Program Annual Report: FY 2003

Introduction
Genetic Improvement
Integrated Aquatic Animal Health Management
Reproduction and Early Development
Growth, Development, and Nutrition
Aquaculture Production Systems
Sustainability and Environmental Compatibility of Aquaculture
Quality, Safety, and Variety of Aquaculture Products for Consumers

Introduction

The Aquaculture National Program NP 106 had another great year with expanded program, scientific productivity, and recognition of scientific quality. The FY 2003 appropriations expanded aquaculture research in five of the seven research program components areas. ARS implemented a new program on genetic improvement of North American Salmon at the National Cold Water Marine Aquaculture Center, Orono/Franklin, Maine.

A new Action Plan was posted on the Aquaculture National Program (106) home page. This new Action Plan is the product of the Joint ARS/CSREES Program Planning Work Shop held in St. Louis, Missouri, November 20-22, 2002. The writing teams are complimented on the comprehensiveness and quality of the document. The Aquaculture National Program is in the first phase of scientific peer review with prospectuses in the process of being written.

The Catfish Genetics Research Team received an USDA, ARS Technology Transfer Award for creative, sustained, and effective research leading to the development, evaluation, and transfer of NWAC103 catfish line to the commercial catfish industry.

Welcome to 4 new permanent full-time scientists (Ric Barrows, Gibson Gaylord, Richard Eaton, and Charles Wierich) who joined ARS in 2003 to work on aquaculture. Four proposals for post-docs (Class of FY 2004) were awarded to scientists in the Aquaculture National Program.

ARS scientists delivered 15 invitational scientific presentations at national and international conferences. The Agency helped support five symposia, workshops, field days or annual association meetings through partial funding, participation, sponsorship or hosting on use of fishery byproducts, sources of protein for fish feed, genetic improvement of striped bass, re-circulation aquaculture forum and trout production.

Three new patents were filed with the ARS Patent Committee.

Genetic Improvement

Since there has been limited genetic improvement of aquaculture stocks, there are major opportunities for improvement through traditional animal breeding, broodstock development, germplasm preservation, molecular genetics, and allied technologies. ARS research addresses improvement of growth rates, feed efficiency, survival, disease resistance, fecundity, yield, and product quality; genetic characterization and gene mapping; and conservation and utilization of important aquatic germplasm.

Breeding project initiated for North American Atlantic salmon. Genetically improved Atlantic salmon lines selected for multiple economically important traits and derived from North American germplasm are important for the viability and continued growth of the commercial U.S. salmon industry. Program funding to initiate research was obtained in 2003 and a Research Leader was hired to develop temporary facilities to initiate the breeding program and plan construction of permanent facilities. The applied breeding program in the ARS National Cold Water Marine Aquaculture Center, Orono/Franklin, Maine will initially focus on growth, but also evaluate other commercially important traits.

A physical gene of map the rainbow trout genome. The effective use of molecular technology to assist development of genetically improved strains of rainbow trout requires that the DNA markers and the genes affecting economically important traits be located on the chromosomes. This is most successful through the use of bacterial artificial chromosomes (BACs) that are pieces of chromosomes (DNA) that have been cloned into a bacterial vector and provide a smaller, more workable subunit of the larger chromosome on which to locate genes and identify physical associations. Utilizing a BAC library produced from rainbow trout for the National Cool and Cold Water Aquaculture Research Center, Leetown, West Virginia, scientists have identified BAC clones that contain genes of interest using known genes and cDNA from their rainbow trout expressed sequence tag (EST) library. A protocol for DNA fingerprinting and assembly of the BACs based on amount of overlap between them has been developed and applied to the BAC library. This enables identification of the most informative BACs from several that harbor the same genomic region and will be an important tool for assembling a physical map for the entire rainbow trout genome. Such a physical map will be needed to clone and work with genes affecting traits of economic importance in rainbow trout.

Foundation strains of rainbow trout performance tested. Evaluation of germplasm and development of brood-stock lines is critical to genetic improvement of economically important traits such as growth, nutrient utilization efficiency, and stress and disease resistance for the rainbow trout industry. Scientists at the National Cool and Cold Water Aquaculture Research Center, Leetown, West Virginia conducted performance evaluations for growth and feed intake on 2002 brood-year fish and started a 2003 brood-year population with four rainbow trout strains. A total of 84 families are in the 2003 brood-year population. These fish represent the parental generation (P1) of a combination of genomes that complement the germplasm already available and provide additional genetic variation on which to base a selection program to improve important production traits.

Established basis of a breeding plan for rainbow trout. Genetic variation is imperative for selective change in natural and captive populations of animals. Samples from three strains of mature rainbow trout that were used for establishing the NCCCWA broodstock in 2002, were analyzed by scientists at the National Cool and Cold Water Aquaculture Research Center, Leetown, West Virginia for nine polymorphic DNA microsatellite loci to determine the amount of variation within, and differentiation among the strains. Analyses of the results demonstrated that all strains appeared to be genetically unique and that a greater scope for selective improvement in multiple traits would be obtained by making a synthetic strain combining the three strains rather than selecting within one of the strains. The outcome of this work provides direction for the breeding plan to improve rainbow trout.

Probability high for Improving feed utilization by rainbow trout. Nutrient utilization efficiency is a key concern of rainbow trout producers because of feed cost and the need to maintain environmental quality standards of water from rainbow trout farms. Scientists at the National Cool and Cold Water Aquaculture Research Center, Leetown, West Virginia conducted a project to identify fish with superior nutrient utilization efficiency and measured the genetic component of this trait. Significant variation among strains was identified for feed efficiency. Improvement of rainbow trout for increased feed efficiency will reduce production costs and help producers become more environmentally sustainable and economically competitive..

Collaborative effort speeds-up functional genomics for rainbow trout. The rainbow trout EST library developed by scientist at the National Cool and Cold Water Aquaculture Research Center contains 45,000 sequences and defines the functional identity of these sequences essential for using this information to assist in producing genetically improved strains. Completion of such an undertaking requires the input of large numbers of researchers. A Rainbow Trout Gene Index was established in collaboration with The Institute for Genome Research and was initially made available to the public in April 2003; an update of the original submission was conducted in June 2003. This provides a very large quantity of molecular DNA information to the scientific community and combines gene sequence data with that from many international projects. This collaborative information will greatly enhance the functional definition of the sequences and speed-up progress on rainbow trout functional genomics.

Incorporating disease resistance into rainbow trout. Disease outbreaks cause large losses during production of rainbow trout. Genetic characterization of the rainbow trout immune response and identification of the genes that influence disease resistance will provide information on mechanisms that can be used to combat pathogen infections. In all agriculturally important species the Major Histocompatibility Complex (MHC) has been shown to be the gateway to immune responses and scientists at the National Cool and Cold Water Aquaculture Research Center, Leetown, West Virginia have mapped clones from their BAC library that contain MHC genes and have begun sequencing the most informative clones. This is a collaborative effort with the University of Maryland's Marine Biotechnology Institute in Baltimore, MD, and will lead to the sequence of the entire trout MHC regions. Such information will provide a better understanding of the response of the rainbow trout immune system and point to future approaches for developing disease resistance into rainbow trout.

The evaluation of cortisol and performance. It is well accepted that stress has a negative impact on many traits in rainbow trout that are important to aquaculture production, including growth rate, feed efficiency, disease resistance and reproductive performance. Although stress response, as measured by blood levels of the hormone cortisol, is highly heritable and lines of low and high responding fish can be generated, investigations into the performance benefits of altered stress response via breeding have been inconclusive. Families of rainbow trout from the broodstock development program that differ by about 2X in cortisol response to stress have been identified and will be evaluated for a variety of performance traits as well as several additional measures of stress response. Positive correlation between stress response indicators and performance traits will provide the information on which to base selection to address the negative effects of stress in aquaculture production.

Knowledge of genes of catfish increasing. Knowledge of catfish genes at the DNA level is limited. Scientists at the Catfish Genetics Research Unit, Stoneville, Mississippi submitted 18816 DNA samples for sequencing and 16416 multiplexed samples for genotyping. To date, this has led to submission of 7833 EST sequences to GenBank. Increased knowledge of genes in the form of BACs and ESTs sequences will assist in the development of microarrays and permit identification of genes controlling economically important traits of catfish.

Further improvement of a select line of channel catfish. Genetically improved catfish lines selected for multiple economically important traits are important for the viability and continued growth of the commercial catfish industry. The applied catfish breeding program in the Catfish Genetics Research Unit at Stoneville, Mississippi, developed a genetically improved catfish line simultaneously selected for growth, feed consumption, processing yield, early sexual maturity, and bacterial disease resistance. Two generations of selective breeding was combined from family ranking of approximately 100 full- and half-sib USDA103 line catfish families from 1999 year-class spawns and approximately 85 families from 2001 year-class spawns to produce a select line. Parentage of spawning fish was obtained from inheritance of microsatellite markers, and this select line will be evaluated and compared to control line USDA103 fish to determine potential performance increases over the previously released strain to commercial producers and consumers.

Integrated Aquatic Animal Health Management

Despite progress in aquatic animal health, significant losses to diseases still occur. ARS research addresses improvement of survival, growth, vigor, and wellbeing of cultivated aquatic animal stocks through integrated aquatic animal health research, improved technologies and practices, such as population health management; and development of health management products, including vaccines and therapeutics, and disease detection/diagnostic techniques.

Model system to evaluate efficacy and approval of therapeutants. Field efficacy trials are not typical for treatment of diseased fish in aquaculture ponds. A model system was designed by scientists at the HKD Stuttgart National Aquaculture Research Center at Stuttgart, Arkansas to simulate the pond environment for use in field efficacy trials to study the effect of copper sulfate and potassium permanganate for controlling mortality associated with ichthyophthiriasis in channel catfish. Studies with copper sulfate in local pond water were conclusive of efficacy, and results indicate that half of the recommended dose of copper sulfate is needed to effectively control an occurrence of ichthyophthiriasis. This information will be crucial to extension agents and farmers as it will prove copper sulfate to be more cost-effective as a disease treatment and for the future of copper sulfate as an FDA-approved aquaculture therapeutant.

Molecular methods used to clarify misidentified F. columnare. Columnaris is the second most costly infection to the channel catfish industry; however, there is no reliable diagnostic technique to definitively identify the causative agent (Flavobacterium columnare) of the disease. Phylogenetic analyses were conducted by scientists at the Harry K. Dupree Stuttgart National Aquaculture Research Center, Stuttgart, Arkansas on the 16S RNA gene of F. columnare isolates and different F. columnare related species. A molecular technique based on the 16S RNA gene was developed to definitively identify F. columnare. An American Type Culture Collection isolate that was misidentified in earlier literature was also correctly identified. The development of a reliable definitive identification technique is a crucial step to control the disease and has demonstrated the importance of molecular epidemiological in fish health management..

Data package on Copper Sulfate Completed. FDA-approval of copper sulfate as an aquaculture therapeutant requires data packages for product chemistry, mammalian toxicology, efficacy, human food safety, target animal safety, and an environmental assessment. All of these data packages were submitted by scientists at the Harry K. Dupree Stuttgart National Aquaculture Research Center, Stuttgart, Arkansas and have been accepted, with the exception of the target animal safety and the environmental assessment. A target animal safety study has been completed, with copper sulfate demonstrating that it is very safe for channel catfish; the report has been written and will be submitted for review. This information will be a required part of the data package used to approve copper sulfate as an aquaculture therapeutant by the U. S. Food and Drug Administration.

Hydrogen peroxide improves catfish hatchability. Little is known regarding biological and environmental effects on the efficacy of hydrogen peroxide as an egg therapeutant. Scientists at the Catfish Genetics Research Unit, Stoneville, Mississippi assessed the effects of embryo developmental stage, hybridization, and water temperature on treatment efficacy. As a result of this research, hydrogen peroxide treatment methods have been optimized to account for differences between channel and hybrid catfish under different culture temperatures, and dependant upon developmental stage at the time of treatment. By following management recommendations, commercial catfish producers could realize as much as a 30-40% increase in annual fry production.

Improving stress tolerance in catfish. Cortisol is a primary stress hormone in all aimals. Stress and/or cortisol adversely effect feeding, growth, disease resistance, reproduction, and overall fish health. Cortisol secretion and clearance rates were investigated in channel catfish as an initial step toward elucidating the regulatory mechanisms involved in cortisol metabolism. The results of this research suggest that cortisol secretion can continue for some time after removal of the stressor, and that the continued increase is due to continued secretion. This research provides the foundation for developing stress-reducing handling methods, and for selecting broodfish with improved stress tolerance.

Polymerase Chain Reaction used to detect Flavobacterium columnare. A rapid polymerase chain reaction (PCR) based detection test for Flavobacterium columnare was developed and evaluated using isolates of F. columnare collected from catfish pond water and from catfish eggs that were experimentally inoculated with F. columnare. Columnaris disease is among the leading causes of catfish mortality. This PCR worked well for the catfish pond water and eggs. This rapid test for columnaris will be further validated by using it on catfish farms.

Protein isolated and characterized to evaluate virulence factors of Flavobacterium columnare. Several major proteins associated with F. columnare have been identified, purified, and characterized to understand virulence. These proteins include a protease, chondroitinase, and phosphatase. The identification, purification, and characterization of these proteins is a significant first step in evaluating virulence factors.

Reproduction and Early Development

Reproduction and early development are important aspects of species domestication and sustainability. ARS research on this component interacts with several of the other components of the Aquaculture National Program. The selection below exemplifies the multi-disciplinary character of husbandry research.

Improved rotifers production for fingerlings. Production of many species of fingerling fish in tanks requires feeding them rotifers or other tiny live food that must be cultured with the use of algae. Scientists at the HKD Stuttgart National Aquaculture Research Center, Stuttgart, Arkansas developed a rotifer culture system that utilizes an automated feeding system to deliver a highly condensed algae paste to feed rotifers. The researchers were able to obtain rotifer densities far in excess of what is expected using traditional rotifer culture. The system uses inexpensive and easily obtainable materials, is straightforward to construct, occupies comparatively little space, is modular and expandable and greatly increases the potential for farmers to be able to culture, on a year-round basis, fingerlings of hybrid striped bass and other fish that require rotifers.

Nitrogen fertilization better than phosphorus for improving productivity of nursey ponds. Commonly used fertilization practices for catfish nursery ponds were developed over 40 years ago. Mississippi State University scientists at the National Warmwater Aquaculture Center, Stoneville, Mississippi compared the responses of phytoplankton and zooplankton to various fertilization methods in catfish nursery ponds. Ponds responded more to nitrogen additions than phosphorus additions, and increasing nitrogen application stimulated the phytoplankton bloom more quickly and significantly increased preferred zooplankton densities. Dramatically changing previous pond fertilization methods can increase the densities of important zooplankton, improving fry growth, survival and health.

Catfish fry graze on the largest zooplankton taxa. Zooplankton populations are important components of the pond ecosystem, yet have been largely ignored in catfish production. Mississippi State University scientists at the National Warmwater Aquaculture Center Stoneville, Mississippi determined zooplankton feeding preferences of catfish fry. Catfish fry showed a preference for the largest zooplankton as soon as they are able to forage. The implication for management of fry ponds is that stocking decisions should not be based on total zooplankton densities, but on the numbers of large zooplankton taxa present.

Growth, Development, and Nutrition

There are substantial opportunities to improve the growth, development, and nutrition of cultivated aquatic organisms. ARS research addresses improving survival, growth rates, feed conversion, environmental tolerances, and feed formulations and feeding strategies to reduce dependence on marine fish-based protein in aquaculture diets.

Protein content can be 25% lower in low- discharge shrimp production systems. Feed represents about half of the total cost of shrimp culture. Understanding of how culture water affects protein and energy requirements in shrimp is important to improving sustainability of shrimp production. Growth and survival of shrimp were compared for ten weeks, using two sources of water (flow-through well water, and static water with high accumulations of suspended particulate organic matter), and diets containing one of four lipid levels (7, 8.5, 10, 11.5%) and one of two protein levels (30% or 40%). Dietary lipid level had no impact on shrimp growth in either of the water systems, although shrimp in the flow-through system fed the 40% protein diets grew better than those fed the 30% diets. In the static water system, shrimp growth did not appear to be affected by protein level. This information provides justification for developing more cost effective feeds containing lower levels of lipid and protein for use in culture systems with low or zero water exchange, and supports this type of culture environment over flow-through systems.

Capability of trout to utilize barley is heritable. Genetic improvement of trout germplasm is necessary for a sustainable enterprise, especially in regards to higher priced feed costs, stricter environmental standards, and increased competition from foreign markets. ARS scientists at the Hagerman Fish Culture Experiment Station, Hagerman, ID have obtained several strains of rainbow trout and distinct families have been evaluated for their growth and utilization of a formulated 40% barley replacement fish feed. More recently selected individuals from superior performing families were crossed and currently their progeny are being tested for growth and diet utilization by both physiological and molecular methods. The generation of rainbow trout strains that demonstrate an enhanced ability to utilize cereal grains in place of fish meal will reduce the cost of feed for farmers, reduce dependence on marine fish stocks for feed and help aquaculture increase its status as sustainable agriculture.

Alternatives to fish meal. Fish meal is an expensive protein source in fish diets and world supplies are limited. The feasibility of using poultry by-product meal, blood meal, feather meal, and two proprietary poultry by-product blends as fish meal substitutes were determined in separate digestibility trials by scientists at the HKD Stuttgart National Aquaculture Research Center, Stuttgart, Arkansas in collaboration with a poultry processor and a fish feed manufacturer. The determined digestibility values for poultry by-product meal, blood meal, and feather meal, as well as two proprietary by-product blends, indicated that these ingredients have potential as substitutes for fish meal in diets for hybrid striped bass. Accurate digestibility values will greatly aid feed manufacturers to cost-effectively use fish meal substitutes in feeds for hybrid striped bass.

Dry feed replaces frozen fish. Some broodstock require frozen fish as a source of essential nutrients to ensure successful egg production; however, reproductive success and biosecurity would be greatly enhanced if dry feeds were available. Trials were conducted by ARS scientists at the Harry K. Dupree Stuttgart National Aquaculture Research Center's Sustainable Aquaculture Systems Research Project at Fort Pierce, Florida to compare reproductive success of broodstock flounder fed formulated dry feeds vs. frozen whole fish diet. Fish fed dry feed preformed equal to fish fed the traditional broodstock diet of frozen fish. These results demonstrate it is possible to successfully spawn flounder on dry formulated feed with reproductive success and enhanced biosecurity.

Cost-effective feed for black sea bass. Optimum growth and efficiency in fish depend on feeds that are balanced to meet nutrient and energy requirements. There is no published information on the nutrient requirements of black sea bass. Protein and lipid are the two most expensive components in fish diets. Scientists at the Harry K. Dupree Stuttgart National Aquaculture Research Center's Sustainable Aquaculture Systems Research Project in Fort Pierce, FL, conducted a study to evaluate multiple protein sources and dietary lipid concentrations for black sea bass for maximum growth and efficiency of black sea bass reared in saltwater. This accomplishment provides information for feed manufacturers to formulate less-expensive and more-efficient feeds for black sea bass.

Aquaculture Production Systems

There are opportunities to improve the performance of aquaculture production systems through development and application of innovative engineering approaches and technologies. ARS research addresses development and successful application to aquaculture of new technologies as well as relevant existing technologies and engineering presently employed in other sectors of the economy.

Zero-water discharge system improved for shrimp production. Optimum feed and culture management practices in a high stocking density, zero-water exchange shrimp culture system is important for the shrimp industry to achieve sustainable goals. A growth experiment was conducted by scientists at the Oceanic Institute(OI), Waimanalo, Hawaii using a prototype feed (30% protein) that was compared to a commercial feed. The OI culture system tanks (circular, flat-bottomed, 1.52 m diameter and 1.15 m3 volume) were equipped with Aquamats to augment natural biota productivity and bead filters to remove solid and toxic wastes. Tanks were stocked with 1.8-g shrimp at very high density (208 shrimp/m2). Shrimp fed the OI prototype feed averaged 21% higher growth, 22% higher survival rate, and 18% larger final weight compared to shrimp fed the commercial diet, reflecting an average yield of 3 kg/m2 or 4.8 kg/m3 for the OI feed, vs. 2.1 kg/m2 or 3.3 kg/m3 for the commercial feed, or a 45% higher yield for the OI feed. This finding represents a significant improvement in our understanding of diet and system interactions, and provides a benchmark for future development of feeds, feeding strategies, and culture management practices for intensive shrimp production in an environmentally friendly system.

Low-cost control of bird predation. Double-crested cormorant and other bird predation on cultured fish is often cited as a major economic loss for the aquaculture industry. Using six privately owned catfish production facilities across a large area within southeastern Arkansas, scientists at the HKD Stuttgart National Aquaculture Research Center, Stuttgart, Arkansas evaluated the effectiveness of a low-cost, physical barrier system for deterring fish-eating birds under commercial settings. The technique limited cormorant access to aquaculture ponds by 4 to 10 fold, prevented other fish-eating birds from landing at similar rates to complete exclusion at some farms, and limited the duration cormorants stayed on ponds. This economical, non-lethal method has gained industry support with at least 10 major catfish farms now employing this approach to greatly reduce losses of cultured fish by double-crested cormorants and other fish-eating birds.

Fillet yield 3 % higher for sunshine than for palmetto bass. U.S. farmers of hybrid striped bass grow one of two commercial crosses with very little objective information about the advantages or disadvantages of producing either one. In cooperation with a regional hybrid striped bass producer, pond production characteristics (feed consumption, feed conversion rate, growth, and fillet yield) of the two crosses were determined by scientists at the HKD Stuttgart National Aquaculture Research Center, Stuttgart, Arkansas. Results indicated that fillet yield was 3% greater for sunshine bass (white bass female x striped bass male) than palmetto bass (striped bass female x white bass male), whereas all other production characteristics were not significantly different. This information suggests to producers that sunshine bass can be more profitable to grow than palmetto bass due to a greater proportion of edible flesh.

Reducing stress during handling and transport of striped bass. Stress as reflected from secretion of plasma cortisol during fish handling can decrease growth and increase disease susceptibility in fish. Scientists at the HKD Stuttgart National Aquaculture Research Center used standardized stress tests, several anesthetics and a wide range of temperatures to determine the conditions under which cortisol levels increase in hybrid striped bass during handling. Metomidate, an anesthetic, suppressed cortisol secretion, and temperatures of 50 to 60° F also suppressed cortisol. The knowledge that hybrid striped bass should be maintained at 50 to 60° F during handling and transport will be useful to reduce economic losses.

Feed efficiency maintained at larger body weights. Minimum size of channel catfish accepted at processing plants has increased, yet farmers lack basic production information for growing larger (> 1.25 lb) food fish in ponds where the catfish population is composed of fish that range from several ounces to near market weight in size. Scientists at the ARS Aquaculture Systems Research Unit, Pine Bluff, AR, in collaboration with a scientist at the University of Arkansas at Pine Bluff Aquaculture/Fisheries Center of Excellence conducted research to quantify growth, feed conversion, and production economics to produce channel catfish of greater than 1.25-lb average weight in ponds stocked with 4-6" fingerlings and 0.5-lb sub-marketable fish. Results showed that channel catfish grow rapidly to average individual weights of 1.25, 1.75, or 2.25 lb, that feed-conversion efficiency was maintained across size classes, and that gross yield of catfish increased from 5,942 to 9,892 lb/acre as fish size increased. Results were presented at the biennial Catfish Farmers of America Research Symposium to give farmers information for modifying farm production strategies to produce larger fish in a cost-effective manner.

Sustainability and Environmental Compatibility of Aquaculture

The overall goal of ARS research in this area is to protect and conserve the nation's water resources and natural environments by conducting research and technology transfer to improve the sustainability and environmental compatibility of aquaculture production systems.

Commercial-scale re-circulation system is operational. Expansion of aquaculture is significantly constrained by the impacts of biological and physical exchanges and other undesirable interactions between open fish farm production systems and the external environment. Scientists at the Conservation Fund's Freshwater Institute (Shepherdstown, WV) are designing and evaluating sustainable land-based finfish production systems that utilize intensification and water recycling technology consistent with biological, environmental and food security objectives. A commercially relevant scale re-circulating fish farm system continuously produced a ton of marketable coldwater finfish per week, demonstrating a practical land-based alternative to ponds, net pens or race-ways. Domestic and international commercial fish farm operations producing Atlantic salmon smolts, Arctic char, ornamental fish, tilapia, rainbow trout, walleye, yellow perch and hybrid striped bass have adopted production systems designs and altered management based on research results from this project.

Phosphorus and bio-solids removal from re-circulation systems feasible. Phosphorus discharged by aquaculture systems, one of the nutrients of high regulatory concern due to its impact on receiving bodies of water, is primarily contained in the filterable or settle-able bio-solids fraction discharged from fish farms. Scientists at the Conservation Fund's Freshwater Institute, Shepherdstown, WV conducted standard jar test studies to evaluate the effectiveness of several commonly used coagulation-flocculation aids at removing both suspended solids and phosphorus from the relatively concentrated microscreen drum filter backwash flow from an intensive re-circulating aquaculture system. Dosages, mixing speed and time, and flocculation conditions for applying alum, ferric chloride, and high iron concentration acid mine drainage (AMD) sludge amendments were optimized to effect maximum removal of both suspended solids and phosphorus from microscreen drum filter backwash flows. Application of coagulation-flocculation chemicals will improve capture of fine solids and total phosphorus in the overflow from aquaculture bio-solids thickening and settling treatment systems.

Impact of 1.5 mg/L dissolved oxygen on catfish production. Research was conducted to evaluate the effect of minimum dissolved oxygen (D.O.) concentration on catfish food consumption, growth and production. Scientists at the Catfish Genetics Research Unit in Stoneville, Mississippi conducted research in six 0.25- acre ponds and collaborating scientists at Mississippi State University conducted research in fifteen 1.0-acre ponds at the Delta Western Research Center at Indianola, Mississippi. Allowing the dissolved oxygen to fall to 1.5 mg/L before commencing aeration reduced feed consumption by 45.1%, growth by 30.5% and net catfish production by 54.0%; at higher dissolved oxygen concentrations, a net production of 23,547 kg/ha was achieved. Preliminary management recommendations are being made available to the industry while research continues on this topic.

New environmental management system achieves 80 % reduced mass discharge. The United States Environmental Protection Agency recently announced the decision to develop nationally applicable discharge standards for aquaculture. Mississippi State University scientists at the National Warmwater Aquaculture Center in Stoneville, Mississippi, responded by evaluating a simple environmental management system to reduce the amount of waste produced within catfish ponds and decrease the volume of water discharged from ponds. After 2 years of study, average mass discharge of total nitrogen, phosphorus, suspended solids, and 5-day biochemical oxygen demand has been reduced by over 80% in ponds managed with the system. Catfish farmers can easily adopt these practices, which will allow catfish farms to be operated with little or no impact on the environment.

Quality, Safety, and Variety of Aquaculture Products for Consumers

The overall goal of ARS research in this area is to improve the quality, safety, and variety of aquaculture products through research and technology transfer. ARS research addresses improvement of the safety, freshness, flavor, texture, taste, nutritional characteristics, and shelf life of cultivated fish and shellfish, and development of new and improved value-added products and processes.

Specialty feeds from fishery byproducts. Knowledge of the chemical content and properties of fish byproducts is needed for the development of value-added products. Detailed chemical content and nutritional properties of pollock, cod and salmon fish processing byproducts (heads, viscera, frames, and skins) was performed by ARS scientists at the Subarctic Agricultural Research Unit, Fairbanks, Alaska in collaboration with scientists at the University of Alaska, the National Marine Fisheries Service, and

the University of Idaho. Determinations were performed on product tissue components content, amino acid profile, calculated rat protein-efficiency ratio, pepsin digestibility, mineral content, and percent soluble protein as altered by pH and temperature. Results indicate the potential to create specialized feed ingredients to fit niche markets by using different byproducts or by combining certain byproducts to create higher valued products.

Impact of herbicides and defoliants on aquaculture. Much of the pond culture of fish in the United States takes place in proximity to cotton culture that often requires the use of aerially applied herbicides having the potential to adversely affect fish in culture ponds by damaging pond organisms and water quality. Scientists at the HKD Stuttgart National Aquaculture Research Center, Stuttgart, Arkansas in collaboration with scientists at the University of Arkansas at Pine Bluff, determined the effects of seven commonly used cotton herbicides and defoliants at various concentrations on pond water quality, phytoplankton and zooplankton. Only Diuron used as either an herbicide or as a defoliant caused reductions in zooplankton levels and algae to the extent that dissolved oxygen levels decreased to levels adverse to fish health. This information allows cotton farmers to make informed decisions about the application of Diuron in fields adjacent to fish ponds.

Preventing exercise at harvest improves fillet quality. Rested-harvesting (sedated-harvesting) of channel catfish could improve fillet quality by avoiding the physiological responses of farm-raised catfish to exercise and stress common during fish harvest and transport. Isoeugenol (a product currently undergoing FDA approval for use in foodfish with zero withdrawl time) was used by scientists at the Catfish Genetics Research Unit at Stoneville, Mississippi in cooperation with scientists at New Zealand Crop and Food Research to determine effects on physiological responses and fillet quality of channel catfish. Isoeugenol minimized the stress and exercise of fish during harvest, reduced detrimental physiological responses associated with typical harvest, and resulted in fillets with improved color and texture. Rested-harvest has potential to benefit catfish producers, processors, and consumers by providing a higher quality fillet.

Using succession to predict a problem. Understanding is needed of the complex interrelationships among bacteria, cyanobacteria, algae, and other zooplankton in catfish aquaculture ponds in the context of off-flavor production. Scientists at the Southern Regional Research Center, New Orleans, Louisiana initiated an 18-month field study of a commercial catfish farm in southern Louisiana in which 20 ponds are sampled weekly. The muddy, musty off-flavor compounds, geosmin and 2-methyl-isoborneol produced by pond cyanobacteria and algae were determined in the pond water samples by gas chromatography/mass spectrometry (GC/MS) The deoxyribonucleic acid (DNA) of the organisms in these samples were analyzed to identify the species that are present. Determining the succession of micro-organisms in the pond water will allow more lead time for farmers to harvest or treat if predictor species precede problematic species.