Effect of Nile tilapia on plankton community and primary productivity of freshwater microcosms

Abstract

Abstract: In this paper, the effect of varying densities of Nile tilapia, Oreochromis niloticus,on structure and function of freshwater microcosms is studied. The results show thatthe predation of Nile tilapia induces the decrease of zooplankton density and results in the increase of phytoplankton denslty,primary productivity and P/Rratio. In the meanwhile, the transparency of water column is decreased andits pHvalue is increased, which induces the water body of freshwater microcosms becoming eutrophic in the later period of experiment. There are significant differences in plankton densities and P/Rratios among all or part of the microcosms with tilapia, but their primary productivity, final physicochemical condition and fish harvest are about the same. Therefore, the changes of community structure and metabolism in microcosms under experimental conditions are not well consistent with the predictions from trophic cascade hypothesis ,indicating that the microcosms is regulated or controlled by both predation (top-down effect and physico-chemical factors (bottom-up effect). It is inferred that if stocking greater density of Nile tilapia, the eutrophication process of natural water body under greater nutrient loading will be speeded up.

Key words: Microcosms, Nile tilapia, Plankton community, Primary productivity

Ruan Jingrong, Rong Kewen, Wang Shaomei, Liu Quxia . Effect of Nile tilapia on plankton community and primary productivity of freshwater microcosms[J]. Chinese Journal of Applied Ecology, 1993, 4(1): 65-73.

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