The scientific lecture with the title of "Effect of cage fish farming on the environment of the Caspian Sea" was presented by Dr. Siamak Bagheri in the conference hall of the research institute. Since the beginning of the 1990s, the Caspian Sea ecosystem has been severely affected by human activities and environmental pollution. Due to the increasing use of fertilizers and pesticides in agriculture and deforestation, the concentration of nutrients in the river has increased and its amount has multiplied in recent years. Few studies have been conducted on the effects of fish farming on the ecosystem of the Caspian Sea, due to the young age of this industry on the southern shores of the Caspian Sea. The aim of this study was to investigate the changes in the structure of plankton and comb jelly populations as well as the amount of nutrients around the sea cages used for fish farming located in the south of the Caspian Sea, Caspian coast. The results showed that the density of phytoplankton in the stations adjacent to the sea cages was higher than that in the reference stations. Also, non - native species are more abundant in stations adjacent to fish farming cages than in reference stations or away from cages. In this study, for the first time in February, 2020, a new non - native species of comb jelly with the scientific name of Beroe ovata Mayer 1912 was observed at stations adjacent to fish farming cages that feed on M. leidyi. The results showed that the density of B. ovata was higher in the stations adjacent to the cages. It seems that the increase in the amount of nutrients due to feeding and fecal waste from fish farming in cages is one of the main reasons for the increase in the abundance of M. leidyi and the emergence of a new non - native species of B. ovata at the stations near the fish farming site. Since the present study was conducted on a small marine cage aquaculture site, in any case, the implementation of a project to assess the environmental impact of cage fish farming on the sensitive ecosystem of the Caspian Sea is recommended due to the development of fish farming in recent years.