Trophic structure and energy fluxes in a grass carp (Ctenopharyngodon idellus) cultured pond ecosystem

A grass carp (Ctenopharyngodon idellus) cultured pond in east China was described using an Ecopath with Ecosim (EwE) model, aimed at characterizing trophic structure, the interactions among ecological groups and assessing the efficiency of the pond ecosystem. Fifteen functional groups were incorporated into the model (including artificial feed). Values for production, consumption and respiration were compared with the total system throughput. The results indicated that both primary and secondary productivity were not well utilized in the pond ecosystem, resulting in an accumulation of detritus. The maximum trophic level of any functional group in the model was only 3.14. This indicates a short food chain, typical of simple or immature food webs in terms of structure and dynamics. The different size fractions of phytoplankton made different contributions to the system, and larger-sized phytoplankton were easier to eat by organisms at higher trophic levels. The study indicated that introducing a polyculture system would increase the efficiency and outputs from the pond ecosystem.