Nutritional components of forage-based food systems and their contribution to growth of juvenile crawfish (Procambarus clarkii)

Abstract

Commercial crawfish aquaculture in the United States presently depends primarily on a forage-based food system, with rice (Oryza sativa) being the major forage. More precise nutritional information about this forage-based system should facilitate its management for crawfish production. Therefore, this study was conducted to determine the nutrient composition of rice during decomposition, to determine the gross trends in biomass of associated microorganisms and their effect on crawfish growth, and to estimate the contribution of separable fractions of available food resources to crawfish growth. A three-part approach was undertaken to address these objectives. In part one, preboot rice (variety Mars) underwent aerobic decomposition at 22.5[plus or minus]1.5°C with pond water and 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 while ash, cell-wall and protein contents increased over time. The second part of the research consisted of a series of feeding experiments in a flow-through tank system to assess the contribution of single feedstuffs to growth of juvenile crawfish (Procambarus clarkii) housed individually. The ability of juvenile crawfish to use plant components for growth was limited, compared with their ability to use a prepared feed (Dupont's Crawdeaux[TM]); and, their ability to use detritus varied directly with the total biomass of associated microbes. The last part of the research focused on crawfish growth in static-water microcosms with and without various components of the detrital food chain and the prepared feed. The growth data were used to fit a multiple linear model with zero intercept to estimate contribution to growth from separable components of the treatments. These were--in order of importance--prepared feed, microbially-enriched detrital forage, soil benthos, soil substrate and possibly meiofauna and larger organisms associated with detritus.