The impact of rainbow trout culture in floating cage on structure of phytoplankton community in the Abbas Abad area, southern basin of the Caspian Sea

This study was designed to determine the effect of rainbow trout culture in floating cage on the distribution and structure of Phytoplankton community in the Abbas Abad area, southern basin of the Caspian Sea. For this purpose, water and phytoplankton samples were collected by a distances of 5, 50, 100 and 1000 m from the cage culture during December 2014 (pre cage), March and April (production period) and August 2015 (post cage). The results of physicochemical factors of water showed that most of the measured parameters had significant differences only among different sampling periods (P<0.05). In this study, 42 taxa of phytoplankton belonging to five phyla (with the dominance of Bacillariophyta) were identified. The results showed that the abundance of most dominant phytoplankton samples had a significant difference during different periods (P<0.05), but this significant difference between different stations was observed for few species studied only. Also, the results of determining the effect of environmental factors using CCA test on the Bacillariophyta abundance showed a minor impact and a positive correlation with turbidity and total nitrogen, While the effect of temperature and ammonium on its abundance was negative. It seems that the rainbow trout cage culture in the Abbas Abad region had a minor impact on water quality factors and nutrients concentration probably due to short duration of cage culture activity and high velocity currents, but no remarkable effect on phytoplankton structure in the vicinity of fish cages, so that the observed changes were more associated with seasonal fluctuant.