Science Serving Maryland's Coasts
Roger Newell, Ph.D.
Horn Point Laboratory
Development of a Heterotrophic Algal Diet for the Aquaculture of Larval Oysters (Crassostrea virginica)
Due to overharvesting and parasitic diseased, the Chesapeake Bay population of oysters has declined dramatically. Aquaculture of oysters is presently impeded in part by the high costs (electrical and labor) of producing large quantities of the microalgal food required by the larval and juvenile life stages. Development of a diet consisting of commercially produced, inexpensive heterotrophic algae would reduce hatchery energy and overhead costs required to produce the phototrophic algae now used.
The effectiveness of algal diets was determined by comparing growth and mortality in larvae fed combinations of commercially produced heterotrophic algae, phototrophically grown algae, and starved controls. The heterotrophic algal diets were successful in raising larvae through metamorphosis, although with a lower growth and survival rate than the phototrophic algal diets.
The effects of resuspension by sonication on the heterotrophic algae was determined using a Coulter Multisizer and by DOC analysis. Sonication increase particle numbers and decreases their size. Resuspended heterotrophic algae solution contains approximately lOx more DOC than phototrophic algal cultures and the heterotrophic algal particles are considerably more dense than the phototrophic algae.
Determination of clearance rates using the Coulter Multisizer proved unsuccessful due to bacterial growth and feces production in the cultures. The use of a Flow Cytometer to determine clearance rates appears possible, but not completed at the end of this study.
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