Aquaculture: Nutrition/Feed Development

The Nutrition Group is interested in crustacean nutrition with the majority of our research being focused on the lobster (Homarus americanus). One of the goals of the program is the development of an optimum nutrient profile for the lobster which will serve as a guideline for a commercial ration. Research is also conducted on defining other nutritional parameters, such as consumption, assimilation, and food conversion, which will be important to the commercial lobster aquaculturist. We have found that addition of a phospholipid (lecithin) to the diet of juvenile lobsters eliminates "molt deaths," which were responsible for up to 70% of the juvenile lobsters that died when fed previous artificial diets. The specific component of lecithin which is essential, was found to be phosphatidylcholine, a compound which lobsters apparently cannot synthesize at a rate high enough to meet their physiological needs. The effectiveness of phosphatidylcholine in reducing mortality related to the molt death syndrome is dependent on the source of the compound. Phosphatidylcholine molecules which are comprised of long-chained polyunsaturated fatty acids are the most effective. Further research has indicated the physiological role of phosphatidylcholine is related to the transport of cholesterol, an essential nutrient for lobsters as well as all other arthropods which are incapable of synthesizing this sterol. Although a basic outline has been developed as to the role of phospholipids in lobster nutrition, a number of detailed questions have yet to be answered as to optimum dietary levels of phospholipids and cholesterol, in order to maximize ration efficiency. Continuing studies will extend these findings, evaluate the effects of other dietary components, and test particular diet mixes in long-term lobster growth experiments. Two graduate students, Michele Bronstein and Karen Norman, are working under the direction of Dr. Conklin in the Nutrition group. Michele Bronstein, who joined the laboratory this summer, is a graduate student at UC Davis, being jointly sponsored by Dr. Duane Brown of the Food Science and Technology Department and by Dr. Conklin, is examining the role of Vitamin D metabolites on the physiology of fish. She is particularly interested in aspects of comparative physiology comparing a typical bony fish, the catfish, and the sturgeon, which although evolutionarily a bony fish, has reverted to the more primitive cartilaginous skeleton. Michele has refined and optimized existing HPLC (High Pressure Liquid Chromatography) techniques, specifically for analyses of Vitamin D metabolites in fish serum. Karen Norman, a Ph.D. student in the Nutrition Graduate group at UC Davis, is investigating amino acid metabolism in the lobster, Homarus americanus. Preliminary feeding trials have indicated that the amino acid profile required by lobsters may be unique. Further investigations will allow for optimization of protein quality in commercial lobster rations, and should help in the movement of lobster aquaculture from the lab to commercial reality.