The current study has evaluated Shatt Al-Arab water using organic pollution index. The study included three stations, the first Al-Sharash, the second Al-Salhiya and the third area Al-Dweab. Water samples were monthly collected from December 2017 to November 2018. Five environmental parameters were used to calculate the organic pollution index (OPI) including Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Active nitrate (NO3), Ammonium ion (NH4) and Total Phosphate (TP). The highest biological oxygen demand was 9 mg.l-1 at Al-Sharash station in July and the lowest values 1mg.l-1 in the Al- Dweab station during December, January, February and April. The highest chemical oxygen demand (250 mg.l-1 was recorded at Al-Sharash station in September and the lowest value was 6.2 mg.l-1 in Al-Dweab station during December. Nitrates was recorded the highest value 41.51 mg nitrogen-nitrate.l-1 at Al-Salhiya station in May and lowest value 1.49 mg nitrogen- nitrate.l-1 at Al-Sharash station during December. The ammonium ion was recorded in highest value 7.7 mg.l-1 at Al- Salhiya station in December and the lowest value 0.5 mg. l-1 at Al-Sharash station during June, while phosphate value was 0.23 and 1.99 mg.l-1 were recorded at Al-Sharash station in August and July respectively. The highest value of organic pollution index was 2.56 at Al-Salihiya station in August and lowest value 0.69 in the Al-Dweab station in April, while the annual rate of organic pollution index for the first, second and third stations were 1.55, 1.81 and 1.47 respectively, and 1.61 for Shatt Al-Arab water.

The digestive tract in Eriocheir sinensis consists of the alimentary canal which includes a foregut consisting of the mouth, esophagus, and stomach. The mouth is surrounded by several pairs of appendages which are specialized for chemoreception and prey capture while esophagus is short and straight moves food from mouth to the stomach, which look like an oval sac divided in to two parts called the cardiac chamber and the pyloric chamber. The composition of digestive tract were investigated and the diet analysis was assessed using two methods: points and frequency of occurrence. The main food items included eight types, the highest percentage of 43.6% shrimp, 42.8 % detritus and 14.5% sand, while the lowest were (0. 39 %, 0.69% and 0.97% for eggs, plants and filament algae respectively. Feeding intensity and activity values arranged between 12 -15.9 and 76 - 86%, respectively, while the Vacuity index were 14 - 31.6%, and Feeding index values were 59.9 - 79.7%.