Effects of cage culture of rainbow trout, Oncorhynchus mykiss on phytoplankton and zooplankton communities (Case study: Golestan Reservoir 1, Gorgan, Iran)

The environmental effects of fish cage culture have poorly been studied in reservoirs. Since this activity is increasingly practiced, investigations on the impacts of cage culture on physicochemical parameters and biodiversity of the reservoir is imperative. The aim of this study was to study the effects of rainbow trout cage culture on water quality, as well as plankton population structure and communities in a reservoir (Golestan Reservoir 1, Gorgan, Iran). Four sampling stations were selected in the following manner: sampling station immediately below the cages, stations some distances including 50 m, 150 m and 1000 m (control station) away from the cages. Phytoplankton, zooplankton and water samples were obtained on a monthly basis for 4 months (December, January, February and March 2016). The depths of the stations were the same. Water temperature, pH, dissolved oxygen, EC, transparency, TDS and TSS did not exhibit statistically significant differences among the stations. Significant increases were detected in the ammonium, nitrate, phosphate and chlorophyll α concentrations at the cage station (P˂0.05). Five phytoplankton phyla including Bacillariophyta, Chlorophyta, Cyanophyta, Euglenophyta and Dinophyta and also four zooplankton phyla including Protozoa, Rotatoria, Cladocera and Copepoda were identified in the reservoir. The obtained results revealed that cage culture exerts significant effect on the population and communities of planktonic organisms. Increase