The effect of cage rearing rainbow trout (Oncorhynchus mykiss) on macroinvertebrates community of southern part of Caspian Sea (Nashtaroud region)

This study carried out to investigate the fluctuation of benthic population in cages of rearing trout (Oncorhynchus mykiss, Walbaum, 1792) in depths of 30-25m of southern part of Caspian Sea at Nashtaroud region of Mazandaran province, This study was performed 150 days with measuring and evaluating physico-chmical factors of water during 5 phases up to the end of rearing period .Samples collected by Ekman Grab was 3 replicates in and out of cages, monthly. In order to investigate population of benthic, some indices such as Shanon-wiver,Simpson and Margalof are used to determine diversity dominance and enriching of species. Totally, 200 specimen of invertebrates (g/m2) belonging to 3 families Bivalvia Molluscas, polychaeta worms and Crustacea collected. The maximum and minimum biomass belongs to Abra ovata 49.2 gm-2 and species like Nereis diversicolor, Balanus improvises and Mytilaster lineatus 1gm-2 respectively. The results of study on organic material showed significant differences in the stations, so that highest was seen in west of cages and the lowest seen inside the cages (P<0.05). There is significant correlation between density and biomass of benthic and percent of mud in the bottom (P<0.05). The results showed positive correlation between Shannon diversity index and biomass of benthic (p=0.001; r= 0.684). Results showed that although after the introduction of salmon cage rearing larvae statistically significant difference was observed in the diversity and density benthoses (P<0.05),but the changes in the diversity of macrobenthose have been very little and partial in the established rearing cages. According to ecological of Classification was done educational platforms studied were placed in stressful and polluted.