Abstract
Using the common carp Cyprinus carpio L. in polyculture ponds to increase both phyto- and zooplankton availability has become a popular practice for the cultivation of plankti - vorous fish, such as rohu Labeo rohita Hamilton. However, the dynamics of how common carp influences the environment and ecology in polyculture ponds are unclear. In the present study, the effects of various stocking densities (0, 0.5 and 1 m �2 ) of common carp on the dynamics of nutri- ents, phytoplankton, zooplankton and benthic macroinvertebrates were investigated every other week over a 137 d period in rohu (density: 1.5 m �2 ) ponds under fed and unfed conditions. All envi- ronmental parameters and all groups of phytoplankton, zooplankton and benthic macroinverte- brates significantly changed over time, although trends in these changes were inconsistent at dif- ferent common carp densities. The correlation between phosphate-phosphorus (PO4-P) and total phytoplankton biomass indicated that the phytoplankton biomass was limited by low PO4-P con- centrations in ponds without common carp. Common carp-driven resuspension increased N and P fluxes from the sediment to the water column and subsequently increased primary and secondary production. A stocking density of 0.5 common carp m �2 had strong effects on nutrients and both phyto- and zooplankton availability, with an increasing trend over time. These effects were par- tially lost in ponds with 1 common carp m �2 , which can be considered as overstocking. This study suggests that an optimal density of common carp can be used as a management tool to manipulate the aquaculture environment for better growth and production of fish.
Highlights
Most of the nutrients in ponds are stored in bottom sediments in both organic and inorganic forms (Briggs & Funge-Smith 1994, Boyd 1995, Rahman et al 2008)
PO4-P and total phosphorus (TP) concentrations in the water and benthic macroinvertebrate availability in bottom sediment increased with increasing time
Time effects on the PO4-P and TP increase were more pronounced in the presence of 0.5 common carp m−2, followed by 1 common carp m−2, and without common carp
Summary
Most of the nutrients in ponds are stored in bottom sediments in both organic and inorganic forms (Briggs & Funge-Smith 1994, Boyd 1995, Rahman et al 2008). According to Biro (1995), sediment can store 100 to 1000 times more nutrients than water. Transference of nutrients back into the water column by the resuspension of sediment can have an important influence on the limnology of ponds (Zambrano & Hinojosa 1999, Rahman et al 2010). Several fish species often resuspend sediment; the Publisher: Inter-Research · www.int-res.com. Aquacult Environ Interact 6: 223–232, 2015 availability for planktivorous fish. Planktivorous fish reduce algal biomass and water turbidity, which in turn has an important impact on photosynthesis (Rahman 2006, Rahman & Verdegem 2007). The combined effect of benthivorous and planktivorous fish on pond limnology is highly complex and has not been well quantified
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