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Aquaculture
Affiliated research principals:
Dr. G. Joan Holt
Mariculture is a rapidly developing scientific and commercial discipline that benefits the way we harvest and
conserve marine fish species. Although great strides have been made, the field is limited by unreliable rearing
systems and impractical diets for larvae and mature fish. FAML works to reliably spawn fish in captivity, determine
essential nutrition, and optimize its supply to enhance fish reproduction, growth and survival. Our Nutrition
studies focus on increasing the quality of both live and artificial food sources, expanding our knowledge of the
nutrient requirements of marine fish across every stage of life. Close relationships with regional resource managers
and aquaculture operations allow rapid handoff of new rearing techniques.
Our spawning research conveys direct benefits to Gulf fisheries right outside our door. Life history traits are
unknown for the majority of Gulf of Mexico fish species impacted by human activities such as offshore gas production,
and fishing. The data we procure on fish reproduction, developmental changes in larval feeding, and physiological
responses to environmental parameters is invaluable for predicting the effects of human actions on coastal ecology.
This work will also provide information that is critical to advancing fisheries management, and develop the technology
necessary for responsible stock enhancement.
Aquaculture Research Areas:
Larval fish:
- Diet optimization [Show Details]
The production of live food for mariculture fish species is costly, unreliable and high mortalities are seen
when larvae are weaned to artificial diets. A key research theme at FAML is the development of effective
early weaning diets. Currently, we are designing and testing diets to wean cobia (Rachycentron canadum ),
red drum (Sciaenops ocellatus), and southern flounder (Paralichthys lethostigma) larvae. Nutrition is paramount to production success, and the design of
specific diets for all life stages is needed. We are working with cobia on the protein requirements and
optimal energy / protein ratios of juveniles. Additionally, we are studying the ontogeny of digestive tracts
in cobia and southern flounder, along with the role of select enzymes. Future work is planned with determining the HUFA requirement of cobia,
evaluating how HUFA affects the ability of cobia to osmoregulate, while examining possible replacements with
terrestrial oil sources.
Other work involves the hormone cholecystokinin (CCK) and its role in the development of the digestive tract
of larval red drum. We are exploring how CCK regulates the release of pancreatic digestive enzymes in larvae
which have not yet developed a stomach. A study of the digestive system of developing larvae suggests that
young cobia can be weaned from live zooplankton to dry diets by 12-14 days of age.
- Density effects in juvenile survival [Show Details]
Future investigations of density dependent survival and growth will improve production of fingerlings. Our goal is to
improve juvenile production by increasing larval survival in high density rearing systems, where density dependent effects
during early survival may be related to the surface area of a tank instead of volume.
- Lipid Nutrition [Show Details]
One method used to determine the specific nutritional requirements of fish larvae is through the use of artificial diets
comprised of varying levels of lipids, proteins, vitamins, etc. Recent nutritional studies utilizing this method have
indicated a high dietary lipid requirement for larvae. The purpose of our studies are to further investigate the
response of larvae to dietary changes in total lipid and fatty acid composition. The growth, survival, and
stress resistance of larvae reared from first feeding to 20 days after hatching have been assessed for live diets
and compared to commercially available artificial diets.
- Alternative Prey Items [Show Details]
Rotifers and Artemia nauplii are currently the standard initial foods in the culture of many species of marine fish.
However, neither of these organisms is naturally rich in PUFAs, which are known to be important in fish nutrition.
Culturing a prey species more able to meet larval fish nutritional requirements would improve the efficiency of fish
hatcheries currently using rotifers and Artemia. This project is aimed at culturing both copepods and dinoflagellates,
and assessing their nutritional value as first foods for larval fish by measurements of larval survival, growth and stress
resistance. Of particular interest are certain copepod species that produce resting eggs, which may allow the development
of a storable larval food similar to Artemia cysts.
Juvenile fish [Show Details]
We are carrying out feeding trials on juvenile cobia (Rachycentron canadum) to test the effects of varying protein/energy
ratios on growth and survival. We are finding that cobia survive and grow well with a lower protein and higher carbohydrate diet.
This is significant because it can lead to a reduction in the amount of fish meal required for commercial production of cobia.
Recent studies with southern flounder have evaluated changes in digestive enzyme capacity in order to determine when changes in dietary
requirements occur during development. In progress are experiments to establish salinity limits to growth for juvenile flounder
in order to identify habitat requirements for young flounder in the estuary.
Relevant Reference:
Faulk, C.K., A.D. Benninghoff and G.J. Holt. 2007. Ontogeny of the gastrointestinal tract and selected digestive enzymes in cobia Rachycentron canadum (L.).
Journal of Fish Biology 70:567-583.
Broodstock & Spawning [Show Details]
FAML is world renowned for conducting research that can provide valuable life history details such as size and age at spawning, fecundity
(number of eggs), density of eggs and larvae, age at first feeding, and growth rates. These life history traits are unknown
for the majority of fish species impacted by humans in the Gulf of Mexico. FAML’s data on reproduction, developmental changes
in larval feeding, and physiological responses to environmental parameters is invaluable for interpreting the response of fishes
to anthropogenic activities, and developing stock enhancement programs. The main objectives of our current spawning research are:
- Spawn economically valuable fish species under natural conditions in captivity to establish fecundity and provide eggs for further studies and stock enhancement
- Determine the buoyancy of eggs and larvae of each of these species
- Evaluate the effects of temperature on survival of eggs and larvae and on growth rates of larvae
- Assess how temperature and salinity affect feeding rates of larvae at different stages
Species currently studied:
Cobia (Rachycentron canadum)
Red drum (Sciaenops ocellatus)
Southern flounder (Paralichthys lethostigma)
Snook (Centropomus undecimalis)
Yellowtail snapper (Ocyurus chrysurus)
Tripletail (Lobotes surinamensis)
In order for the commercial production of any marine fish to be successful, a steady supply of high quality eggs is necessary for grow-out.
Variations in the biochemical composition of fish eggs have been correlated with changes in egg viability and hatch rates, embryo development
and larval survival. Egg composition is dependent upon a variety of factors including inter- and intra-specific genetic differences,
broodstock diet or age, spawning period and environmental parameters such as temperature and salinity. We are currently quantifying the
composition of cobia eggs over multiple spawning seasons and will look for relationships between egg composition and egg viability and
hatch rate. Because broodstock diet and egg composition are often highly correlated, understanding how egg composition and egg quality are
related may provide a stepping stone to the formulation of a quality broodstock diet for cobia.
We are working with Texas Parks & Wildlife to transfer these techniques to the state hatchery for potential stock enhancement if that
should become a priority in the future.
Pertinent references:
Arnold C.R., Kaiser J.B., and Holt G.J. 2002. Spawning of cobia (Rachycentron canadum) in captivity. Journal of World Aquaculture.
33:2.
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