A clupeoid fish Nematalosa nasus (Bloch), inhabiting the Gulf of Aden, Arabian Sea, Hongkong (Whitehead, 1972) is considered an important commercial fish in these regions. This species enters the Shatt a1-Arab River in spring and sometimes reaches further north to the Hor al-Hammar marsh (Whitehead, 1965). The species is found year round in Khor a1-Zubair, the north west extension of the Arabian Gulf.
N. nasus is caught in the Shatt a1-Arab and Khor area and is estimated to contribute 50% of the combined annual clupeoid production.
Variations in meristic characters have been used as a basic tool in separating populations of different fish species (Seymour, 1959; Anthony, 1968). Meristic differences between populations of fishes may be influenced by genetic or environmental factors, or both (Bailey and Gosline, 1955). Different workers attributed the difference in meristic characters to environmental factors such as light, temperature and disolved oxygen during the period from fertilization to hatching (Tåning, 1952; Wallace, 1973; Kwain, 1975).
This study was undertaken to determine whether one or more populations of N. nasus occur in Iraqi and Kuwaiti waters by analyzing variations in meristic characters.