Sixteen Arabian Gulf fish species were recorded for the first time in the mid and upper region or Shatt Al-Arab River, Basrah, Iraq. Most of them are pelagic species, widely distributed in the Arabian Gulf and even in the different seas. They are obviously adapted to rather various environmental conditions. The changing in the chemical, physical and biological characters of Shatt Al-Arab River during the Iraqi-Iranian war may have facilitated recent immigration. A review to the environmental characters of both the Arabian Gulf and Shatt Al-Arab River are given.