Effects of farming practices on the performance of fish pond polyculture assessed by trophic modeling

Abstract

This study aimed to identify species compositions that use resources more efficiently and recommend management practices for extensive and semi-intensive pond polyculture by modeling food webs and calculating performance indicators. We monitored 8 polyculture fish ponds managed by fish farmers that had contrasting fish species compositions in two regions of France and analyzed their biomass flows using the Ecopath model. The ponds that had been stocked with at least 5 species × size classes had the highest net fish yield and nutrient recycling (Finn cycling index [FCI]), which highlighted the importance of diversity and complementarity for increasing resource use, nutrient recycling, and productivity. Carnivorous fish appeared to contribute significantly to net fish yield and nutrient recycling. Ponds stocked with grass carp had significantly higher mean net fish yield, likely because the grass carp occupied an otherwise vacant trophic position. Ecotrophic efficiency (EE) was high for benthic macroinvertebrates (0.90–0.99) and zooplankton (0.55–0.99), which indicated that they can limit pond productivity, but low for phytoplankton and detritus (0.06–0.29 and 0.04–0.17, respectively), which indicated that they were underconsumed. FCI was not significantly correlated with net fish yield but was significantly correlated with the EE of phytoplankton (r = 0.90) and detritus (r = 0.91), which highlighted the importance of these functional groups to nutrient recycling. This study provides insights into biomass flows among species during a production cycle, which could be improved by modeling temporal dynamics of the system. It indicates that nutrient recycling and productivity in fish ponds can be increased by defining the percentages of species more precisely.