The ecosystem of the Caspian Sea have been strikingly changed by human activities. This area has undergone significant ecological alterations and serious environmental degradation since the beginning of 1990s. The impact of fish cage culture on the zooplankton community was studied in the southwestern Caspian Sea, off Jafrud during January to April 2013. A total of 12 zooplankton belonging to 9 taxa were identified at the study area. Only one species of Cladocera (Pleopis polyphemoides), was present in our study. Acartia tonsa and Balanus improvisus were the most dominant species. Bivalvia larvae, P. polyphemoides (Cladocera) and Synchaeta sp. (Rotifera) occurred only in January. The average of zooplankton abundance varied between 1,600 and 14,500 ind.m^-3 in the study. The principal component analysis revealed the spatial variations of zooplankton abundance between the fish cage culture site and the reference site stations. The findings confirmed the impact of fish cage culture on the zooplankton population structure from the prominent abundance of A. tonas, B. improvisus, P. polyphemoides, and Bivalvia larvae at the fish cage site as compared with the reference site. The ecosystem of the Caspian Sea have been strikingly changed by human activities. This area has undergone significant ecological alterations and serious environmental degradation since the beginning of 1990s. The of fish cage culture on the zooplankton community was studied in the southwestern Caspian Sea, off Jafrud during January to April 2013. A total of 12 zooplankton belonging to 9 taxa were identified at the study area. Only one species of Cladocera (Pleopis polyphemoides), was present in our study. Acartia tonsa and Balanus improvisus were the most dominant species. Bivalvia larvae, P. polyphemoides (Cladocera) and Synchaeta sp. (Rotifera) occurred only in January. The average of zooplankton abundance varied between 1,600 and 14,500 ind.m^-3 in the study. The principal component analysis revealed the spatial variations of zooplankton abundance between the fish cage culture site and the reference site stations. The findings confirmed the impact of fish cage culture on the zooplankton population structure from the prominent abundance of A. tonas, B. improvisus, P. polyphemoides, and Bivalvia larvae at the fish cage site as compared with the reference site. The ecosystem of the Caspian Sea have been strikingly changed by human activities. This area has undergone significant ecological alterations and serious environmental degradation since the beginning of 1990s. The of fish cage culture on the zooplankton community was studied in the southwestern Caspian Sea, off Jafrud during January to April 2013. A total of 12 zooplankton belonging to 9 taxa were identified at the study area. Only one species of Cladocera (Pleopis polyphemoides), was present in our study. Acartia tonsa and Balanus improvisus were the most dominant species. Bivalvia larvae, P. polyphemoides (Cladocera) and Synchaeta sp. (Rotifera) occurred only in January. The average of zooplankton abundance varied between 1,600 and 14,500 ind.m^-3 in the study. The principal component analysis revealed the spatial variations of zooplankton abundance between the fish cage culture site and the reference site stations. The findings confirmed the impact of fish cage culture on the zooplankton population structure from the prominent abundance of A. tonas, B. improvisus, P. polyphemoides, and Bivalvia larvae at the fish cage site as compared with the reference site. The ecosystem of the Caspian Sea have been strikingly changed by human activities. This area has undergone significant ecological alterations and serious environmental degradation since the beginning of 1990s. The of fish cage culture on the zooplankton community was studied in the southwestern Caspian Sea, off Jafrud during January to April 2013. A total of 12 zooplankton belonging to 9 taxa were identified at the study area. Only one species of Cladocera (Pleopis polyphemoides), was present in our study. Acartia tonsa and Balanus improvisus were the most dominant species. Bivalvia larvae, P. polyphemoides (Cladocera) and Synchaeta sp. (Rotifera) occurred only in January. The average of zooplankton abundance varied between 1,600 and 14,500 ind.m^-3 in the study. The principal component analysis revealed the spatial variations of zooplankton abundance between the fish cage culture site and the reference site stations. The findings confirmed the impact of fish cage culture on the zooplankton population structure from the prominent abundance of A. tonas, B. improvisus, P. polyphemoides, and Bivalvia larvae at the fish cage site as compared with the reference site. The ecosystem of the Caspian Sea have been strikingly changed by human activities. This area has undergone significant ecological alterations and serious environmental degradation since the beginning of 1990s. The of fish cage culture on the zooplankton community was studied in the southwestern Caspian Sea, off Jafrud during January to April 2013. A total of 12 zooplankton belonging to 9 taxa were identified at the study area. Only one species of Cladocera (Pleopis polyphemoides), was present in our study. Acartia tonsa and Balanus improvisus were the most dominant species. Bivalvia larvae, P. polyphemoides (Cladocera) and Synchaeta sp. (Rotifera) occurred only in January. The average of zooplankton abundance varied between 1,600 and 14,500 ind.m^-3 in the study. The principal component analysis revealed the spatial variations of zooplankton abundance between the fish cage culture site and the reference site stations. The findings confirmed the impact of fish cage culture on the zooplankton population structure from the prominent abundance of A. tonas, B. improvisus, P. polyphemoides, and Bivalvia larvae at the fish cage site as compared with the reference site.