Background

Successful and efficient reproduction is essential for sustainable aquaculture.  There are many opportunities for improving reproduction and early development of cultivated aquatic organisms.  Development of domestic strains with increased fertility will allow more efficient production of aquatic species with desirable culture characteristics and consumer appeal.  Inefficiencies in maintaining viable seedstock, sexing of individuals, storing and utilizing gametes, and maintaining embryos and early life stages limits hatchery production, and utilization and conservation of valuable germplasm.  Suboptimal fertilization rates and poor development during early life stages reduces production efficiency and profitability.  Understanding requirements for proper gamete production and development of early life stages will lead to improved reproduction techniques.  Research efforts will improve the understanding of environmental, neuro-endocrine and genetic factors controlling reproduction in aquaculturally important species, and development of methods to enhance reproductive output, embryo development, and rearing of cultivated aquatic organisms during early life stages. 

Vision

Produce reproductively efficient aquatic strains that require fewer resources, are environmentally friendly, and supply aquaculture products that more fully meet consumer expectations. 

Mission

Research will seek to improve gamete and seedstock quality with year-round availability; improve development and survival during early life stages; and ultimately achieve optimum reproductive efficiency. 

Impact

Decrease overhead and unit cost of production of all aquatic species, resulting in greater profitability for U.S. aquaculture producers and in lower food costs for consumers. 

Linkages

Other USDA-ARS National Programs: 101 Food Animal Production. 

Other Agencies and Departments: U. S. Colleges of Agriculture and State Agricultural Experiment Stations, U. S. Fish and Wildlife Service, and U. S. Food and Drug Administration 

Private Sector: U. S. Aquaculture and Grower Associations. 

Problems to be addressed 

a.  Control of reproduction

Control of reproduction is essential for genetic selection, cost efficient and reliable production of seedstock and product quality.  Currently there are few species where specific seedstock can be induced to produce gametes year-round and the timing of gamete availability is optimal for grow-out strategies or genetic selection efforts.  Furthermore, the percentage of animals successfully producing high quality gametes is low, increasing hatchery costs; while on the other hand, the high energy demands of gonadal development in pre-market size animals reduces product quality and production efficiency.  Reproduction is regulated by environmental factors detected by higher brain centers, which in turn activate the neuro-endocrine system controlling gonadal development and spawning.  There is genetic variation in how the individual animal responds to these signals.  Controlling reproduction requires characterizing then managing the environment for optimum reproductive efficiency, which in turn requires understanding basic neuro-endocrine regulatory mechanisms and gonadal development and function.  Since optimal or even minimal requirements may not be met in captivity, hormonal intervention and other strategies may also be required. 

Goals

1.      Elucidate pathways for neuro-endocrine regulation of gonadal development and function, and identify candidate genes for enhancing reproductive efficiency.

2.      Elucidate environmental influences and the impact of stress on critical control points limiting reproductive efficiency.

3.      Develop methods to identify reproductive stage.

4.      Develop methods to alter timing of reproductive development. 

Approach

1.      Determine mechanisms of neuro-endocrine regulation of gonadal development and function.

2.      Identify genes whose expression is differentially regulated in individuals with enhanced reproductive efficiency.

3.      Determine environmental effects and stress on neuro-endocrine pathways controlling gonadal development and function.

4.      Develop diagnostic tools to identify reproductive stage.

5.      Determine environmental, neuro-endocrine, and genetic influences on the timing of reproductive events that are amenable to manipulation.

6.      Improve hormone delivery systems, the use of probiotics and other strategies for controlled reproductive development. 

Outcomes

• Management strategies and techniques for controlling reproduction and enhancing efficiency, improved reproductive efficiency and on-demand production of gametes.
• Ability to delay, shift, or prevent the onset of gonadal development. 

ARS Locations

• Stoneville, MS 
• Leetown, WV 
• Stuttgart, AR

b.  Control of Gender and Fertility

Among many aquatic species, one gender has characteristics that make it more desirable for food than the other.  The desirable gender for aquaculture is determined by several characteristics and different species may have a different preferred gender.  This difference in sex-associated characteristics can be taken advantage of by developing methods to produce only the desirable sex.  Monosex populations can be produced directly by exogenous hormone treatment if the fish are treated during early development, or by gynogenesis and androgenesis.  Indirect production of monosex populations can be produced by hormonal sex reversal combined with genetic backcrosses, gynogenesis, or androgenesis.  The indirect technique is often more desirable because parental strains are produced, and their progeny are then sold for aquaculture production.  Under some conditions, sterile animals, such as those produced by polyploid induction, are useful in aquaculture.  These animals cannot reproduce if they escape to the environment and often demonstrate increased growth. 

Goals

1.      Identify desirable gender-specific characteristics for aquaculture species.

2.      Determine the conditions by which gender can be controlled.

3.      Develop new technologies and improve current methods to control gender and fertility.

4.      Develop genetic techniques to determine the sex genotype. 

Approach

1.      Determine the type of sex determination model that exists for species important to the aquaculture industry.

2.      Identify protocols that will alter the sex phenotype of developing fish, including the use of hormones, gynognesis, androgenesis, and environmental effects on gender differentiation.

3.      Develop techniques to induce sterility, including polyploid induction.

4.      Develop genetic diagnostic tools to determine sex genotype independent of phenotype.

5.      Determine genetic location and function of gender related genes. 

Outcome

• Monosex seedstock to maximize desirable characteristics for improved production efficiency and market value. 
• Seedstock that can be ownership protected since only the progeny are sold for grow-out. 
• Understanding of gender-related genetic make-up and the plasticity of the sex determining system. 
• Sterile animals to reduce risk of environmental damage will be produced if feasible. 

ARS Locations   

• Leetown, WV 
• Stuttgart, AR 
• Orono/Franklin, ME

c.  Gamete and Zygote Quality

Improvement of gamete quality or zygote (fertilized egg) quality is essential for cost efficient and reliable production of seedstock and genetic selection.  Egg quality is unacceptably low for all fish species.  The multitude of factors contributing to egg quality makes this a particularly difficult problem to address.  Determination of egg quality has genetic and environmental components.  Environmental factors affecting egg quality include but are not limited to improper environmental cues leading to failed neuro-endocrine regulation of gonadal development and function, stress, and diet.  Lacking is an understanding of what makes a good egg or high quality gametes.  Improving egg quality requires understanding basic processes involved in the assembly of the egg, and needs of the developing embryo; then providing the seedstock with the environmental conditioning and nutritional requirements to produce quality gametes (egg and sperm), followed by appropriate methods for spawning and fertilization.

Goals

1.      Elucidate processes involved in gamete production. 

2.      Elucidate environmental and neuro-endocrine influences on processes of gamete production.

3.      Develop methods to evaluate quality of gametes and zygotes.

4.      Identify diets appropriate for optimal gamete quality.

5.      Identify superior seedstock.

Approach

1.      Determine biochemical mechanisms involved in egg protein and lipid synthesis, production, uptake, and processing for optimal egg production.

2.      Determine environmental effects on biochemical and neuro-endocrine pathways controlling egg protein and lipid synthesis, production, uptake, and processing.

3.      Determine mechanisms involved in sperm production, spawning and fertilization that affect zygote quality, and elucidate environmental effects upon these mechanisms.

4.      Determine effects of diet on gamete and zygote quality.

5.      Develop diagnostic tools and indices to evaluate gamete and zygote quality.

6.      Determine characteristics of superior seedstock (genetics, age, size, fecundity, health, stress response).

Outcome

• Management strategies and diets resulting in high quality gametes and zygotes will be developed. 
• Reduced loss from maintaining non-productive seedstock, and reduced mortality during hatchery operations. 
• Reliable methods for identifying high quality seedstock standards will be realized.

ARS Locations

• Leetown, WV
• Stuttgart, AR 
• Stoneville, MS

d.  Gamete and Embryo Storage, Cryopreservation, and Use

Artificial fertilization utilizing stored gametes extends longevity and use of superior germplasm many fold.  However, this technology is currently limited for aquatic species to the cryogenic preservation of sperm.  New and commercially applicable methods for cryopreservation of gametes and embryos could greatly enhance reproductive efficiency.  These new reproductive technologies can further increase the rate of genetic improvement and reduce costs of aquatic animal production.  Storage of embryos, eggs, and somatic cells would enable the preservation of genetic information.

Goals

1.      Develop new and improved existing methods for cryogenic preservation of sperm, somatic cells, eggs, and embryos of aquatic species.

2.      Develop improved methods of in vitro oocyte maturation and fertilization.

3.      Improve developmental competence of embryos.

Approach

1.      Develop freezing and thawing methods that result in improved fertility and survival of cryopreserved gametes and embryos.

2.      Evaluate biological and environmental factors that impact sperm, egg, and embryo survival after cryopreservation.

3.      Develop new technologies to improve fertilization and embryo development.

Outcome

• Reliable methods for cryogenic preservation of sperm, eggs and embryos will be developed.
• Increased reproductive efficiency that expands use of superior germplasm.

ARS Locations

• Stoneville, MS 
• Leetown, WV 
• Stuttgart, AR 
• Ft. Collins, CO

e.  Early Life Stage Development and Survival

Maximum production efficiency requires all fertilized eggs to result in healthy, normally developed offspring that survive and grow to a juvenile stage.  Although 100% survival is unrealistic, survival to a juvenile life stage in many aquatic species is unacceptably low, often less than 10%.  Others are born with developmental abnormalities that contribute to losses throughout development or impact processing and consumer acceptance.  Factors contributing to losses during early life stages and/or inappropriate development are numerous and interacting. 

Goals

1.      Mitigate and prevent abnormal and inefficient growth and development during embryonic and early life stage development of cultured aquatic species.

2.      Improve embryo and early life stage handling, rearing and culture techniques to enhance survival and health.

Approach

1.      Identify genetic and physiological mechanisms causing inappropriate development and poor survival during embryonic and early developmental life stages.

2.      Develop culture techniques, including feeding strategies, and methods to control physiological mechanisms resulting in inappropriate development and poor survival.

Outcome

• Enhanced embryonic and early life stage development and survival. 
• Reduce inputs used to obtain healthy offspring and improve production efficiency and profitability. 

ARS Locations

• Stoneville, MS
• Stuttgart, AR