Current study was conducted in 13 floating cages located in Shatt Al-Arab River bank at Al-Hartha District. Common carp Cyprinuscarpio
of different weights (290-1700 gm) and numbers (400-1047) fish/cage was cultivated in these cages. Observation was also taken from earthen pond at the same location cultivated with common carp, silver carp Hypophthalmichthys molitrix
and grass carp Ctenopharyngodonidella
. Results showed that water temperature range between 30-35 0
C during May-June, 2015 and a range of 36- 38 0
C during July-August, 2015 in floating cages, while in earthen pond there were 1 0
C more. Salinity don’t differ too much during experiment and range between 1.5-3 ppt. Results of earthen pond revealed no fish mortality during experiment for three species cultivated in this pond. Results appeared that fish mortality during May-June don’t largely differed and its ranged between 0.709%-1.861% and there weren’t any relationship between fish mortality and fish weight. Different fish mortality during July-August which ranged between 3.88% for average fish weight of 400 g and total fish mass of 412 kg and 14.75% for average fish weight of 1700 g and total fish mass of 680 kg. Significant correlation (r=0.86) was found between average fish weight and fish mortality.Significant correlation (r=0.72) was also found between total fish weight and fish mortality. From previous results we concluded that there were positive relationship between fish mortality and fish weight during July-August.