NUTRIENT PROFILES OF GREEN AND DECOMPOSED RICE-FORAGES AND THEIR UTILIZATION BY JUVENILE CRAYFISH (PROCAMBARUS-CLARKII)

A series of experiments was conducted to determine the nutrient content of rice during decomposition, the gross trends in biomass of associated microorganisms, and the effects of these components on crayfish weight gain. Rice forage (variety Mars) underwent aerobic decomposition at 22.5 +/- 1.5-degrees-C in pond water with soil for various intervals of time. Nutrient profiles (ash, crude protein, crude lipid, cell-wall content and C:N ratio) of rice and its products of decomposition varied according to plant portion and decomposition time. In general, decomposition decreased crude lipid content and C:N ratio; whereas, ash increased, and cell-wall and protein contents decreased over time after an initial increase. Detrital microbial biomass was highest prior to 7 weeks post-inundation and was limited by phosphorus under the conditions of this study. A series of feeding experiments also was conducted in a flow-through culture system to assess the contribution of single components from fresh and various stages of decomposed rice as well as a prepared feed (Dupont's Crawdeaux(TM)) to weight gain of juvenile crayfish (Procambarus clarkii) housed individually. The ability of juvenile crayfish to use plant components for weight gain was extremely limited compared with their ability to use the prepared feed, and their ability to use detrital rice varied directly with the total biomass of associated microbes.