This 3-year research program is a continuation of a previous study dealing with the elucidation of the absorptive and secretory functions of the crustacean gastrointestinal tract and kidneys. Many crustacean species are undergoing extensive aquaculture throughout the world. One of the major problems with the successful rearing of these animals from egg to market is providing a cost-effective diet that leads to rapid growth. Prior to the initiation of this research program, little was known about the absorptive functions of the crustacean gut and therefore few recommendations could be made concerning the nature of an artificial diet to provide cultured animals. Previous work has used a variety of in vitro techniques to study the various organs of the gastrointestinal tract of these animals to obtain an understanding of how nutrients, minerals, and water are absorbed during normal digestive processes. The present proposal will extend earlier studies by characterizing nutrient transport mechanisms in the major absorptive organ of these animals, the hepatopancreas. Biochemical isolation techniques will be employed to purify gut transporting membranes that bring about the uptake of dietary components to study the characteristics of these uptake processes for comparison with more thoroughly investigated systems in mammals. In addition, cultured cell preparations of the absorbing organs will be used to quantify rates of transcellular absorption of sugars, amino acids, and other important dietary compounds in these animals. The second goal in this research program is to study the processes of nutrient reabsorption by the crustacean kidneys to establish their roles in metabolite conservation. In mammals nutrients in the blood are filtered and selectively reabsorbed back to the blood by the kidneys and in this way potential toxins can be excreted and important nutrients conserved. Whether the same processes occur in the invertebrates as well as defining the characteristics of reabsorptive processes will be examined. Similar membrane isolation and purification techniques and cell culture studies will be employed with kidney cells as will be associated with the gut organs discussed above. This 3-year study will provide a better understanding of how the gut and kidneys of an economically important group of invertebrates contribute to organismic growth. Important basic scientific information about cell physiology will be forthcoming from these studies, as well as potential useful applied results that may aid in the successful rearing of these animals under controlled conditions.
