The effects of grass carp (Ctenopharyngodon idella Val. 1844) on water quality, plankton, macrophytes and benthic macroinvertebrates in a spring pond.

摘要

Due to excessive plant growth in a spring originating from the Sakaryabasi-West Pond in Ankara, Turkey, which supplied water to a trout farm, grass carp was stocked at a rate of 2 fishes/100 m2 in March 2004. The effects of grass carp introduction on the aquatic plants, water quality, plankton, chlorophyll a concentration, and benthic macroinvertebrates were investigated until November 2004. A net cage with a dimension of 7x7x2 m was placed in the pond as the control (without fish). Aquatic plant samples from 8 stations, and water, plankton and benthic macroinvertebrate samples from 2 stations were obtained monthly. Variances due to months and stations were significant (p<0.01) for aquatic plant biomass, dissolved oxygen, pH, total hardness, ammonium nitrogen, nitrate nitrogen, nitrite nitrogen, total phosphorus, chlorophyll a, zooplankton and benthic macroinvertebrates. The cage was covered with the aquatic plants, such as Potamogeton pectinatus, Ceratophyllum submersum and Lemna trisulca. These aquatic plants were preferred primarily by grass carp; thus, these plants completely disappeared in the pond. Filamentous algae, Cladophora sp., Zygnema sp. and Spirogyra sp. decreased in densities, but did not completely disappear in the pond. The aquatic plant biomass increased by 7-fold inside the cage and decreased by 2.5-fold in the pond at the end of the study period. Phytoplankton abundance and chlorophyll a concentration were higher inside the cage than in the pond, whereas zooplankton and benthic faunas were more diverse in the pond than in the cage (p<0.05)..