Distribution and Composition of Benthic-Invertebrate Community at Fish Floating Cages in Tigris River Before Al- Kut Barrier/ Wasit Province, Iraq

Seasonal study was done for the distribution and composition of benthic invertebrate community in three selected sites (S1, S2 and S3) near a fish floating cages in Tigris river before Al-Kut Barrier south Baghdad, during the period from January to December 2014. Some of water quality parameters were measured as following: temperature ranged from 14°C in winter to 32 °C in summer, dissolved oxygen from 5.2 in summer and 9.8 mg/l in winter, pH values from 7.5 to 7.8, salinity from 0.5 in winter to 0.73 mlg/l in summer and water turbidity from 250 in spring to 900 NTU in autumn. The river bottom of study area was clay loan, silt clay, clay loan and clay for sites S1, S2 and S3 respectively. A total of 19 benthic fauna species were identified. Of these 8, 6, 3, and 2 species belonged to Arthropod, Oligochaet, Mollusca and Nematode respectively. There were significant differences shown at S2 (inside cages) for the organic matter 4.7%, and for organic carbon 2.74%, 19 species, the abundance was 813.4 ind/ m2 and benthic biodiversity was 2.86, compared with S1 and S3. Also, S2 was shown the dominance for Arthropod: Insect (46.6%), followed by Oligochate, Mollusca and Nematode (32.9%, 16.5% and 4%) respectively of the total benthic invertebrate density. The results shown increment in benthic invertebrate density and biodiversity inside cages (site S2) compared with the other two sites before and after cages respectively.