Schroeder, G.L., Institute of Animal Sciences, Agricultural Research Organization: The Volcani Center, P.O.B. 6, Beit Dagan, Israel

The natural isotopic ratio of 13C12C (reported as δ C) in plant matter varies predictably among plant types. The isotopic ratio of an animal body reflects the isotopic ratio of the feed metabolized. By selecting inputs to an aquaculture feeding and/or fertilization system such that the components have significantly different δ C values, the relative meta-bolization of each of these inputs by the fish can be measured. In tank-grown Tilapia aurea (δ C = -17), supplied feed (δ C = -18) provided the carbon incorporated into the fish body even though between feedings the fish consumed large quantities of algae (δ C = -22). In penaeid (δ C = -12) grow-out ponds, δ C analyses indicated that selected components of the feed pellet (average δC = -17; components: corn and sorghum δ C ∼ -12, soybeans δ C ∼-25) were metabolized, while the benthic natural foods and other bottom organic matter (δ C = -21) provided little or no input. The value of such information for pond management and nutrition studies is clear. © 1983.