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Turkish Journal of Fisheries and Aquatic Sciences 2006, Vol 6, Num, 1     (Pages: 7-15)

The Effects of Grass Carp (Ctenopharyngodon idella Val., 1844) on Water Quality, Plankton, Macrophytes and Benthic Macroinvertebrates in a Spring Pond

Mine U. Kırkağaç 1 ,Nilsun Demir 1

1 Ankara University, Faculty of Agriculture, Department of Aquaculture and Fisheries 06110 Dışkapı, Ankara, Turkey Viewed : 4208 - Downloaded : 3680 Due to the excessive plant growth in the spring originated Sakaryabasi-West Pond which supplied water to a trout farm, grass carp was stocked at a rate of 2 fish/100 m2 on March 2004 and its effects on aquatic plants, water quality, plankton, chlorophyll a and benthic macroinvertebrates were investigated until November 2004. A net cage with a dimension of 7x7x2 m was placed to the pond as control (without fish). Aquatic plant samples from eight stations and water, plankton, benthic macroinvertebrate samples from two stations were taken monthly. The variance of aquatic plant biomass, dissolved oxygen, pH, total hardness, ammonium nitrogen, nitrate nitrogen, nitrite nitrogen, total phosphorus, chlorophyll a, zooplankton and benthic macroinvertebrates were found statistically significant by months and stations (p<0.01). During the research period, the cage was covered by the aquatic plants such as Potamogeton pectinatus, Ceratophyllum submersum and Lemna trisulca. These aquatic plants were preferred primarily by grass carp and disappeared in the pond. Filamentous algae, Cladophora sp., Zygnema sp. and Spirogyra sp. decreased but not disappeared. The aquatic plant biomass increased 7 times inside the cage and decreased 2.5 times in the pond at the end of the study period. Phytoplankton abundance and chlorophyll a concentration were found higher inside the cage than those in the pond whereas zooplankton and benthic fauna were found to be higher in the pond than those in the cage (p<0.05). Keywords : Ctenopharyngodon idella, water quality, phytoplankton, zooplankton, benthic macroinvertebrate