Population structure of the sillaginid fishes collected from Fao marine environment, marine, estuary of Shatt al-Arab River and the lower reaches of Shatt al-arab river, Basrah, Iraq

Meristic variation among stocks of the two sillaginid species Silago arabica and S. sihama in the lower reaches of Mesopotamia was examined using meristic characters. Non parametric analysis was used to compare meristic traits from freshwater, estuarine and marine environment. Results suggested that there is constrained migration of populations of these two species from the freshwater location through the estuarine and finally the marine environment. Three separated self-recruiting populations of the two sillaginid species were observed one at the freshwater, second at the estuary of Shatt al-Arab and the third population at the marine waters of Iraq. Inspection of the role of each meristic trait variable to analysis showed that changes among samples appeared to be linked with the pattern of distribution of water temperature. The reversal pattern of the number of the scales in the lateral line of S. sihama may be related to the effect of gradients of salinity.