Effect of the salinity gradient on fish assemblage composition in the Shatt Al-Arab River

The effect of the salinity gradient on fish assemblage composition

Abstract

Because there have been only a few studies on the effect of the salinity gradient on the formation of fish assemblages in the Shatt Al-Arab River, the present study was conducted on the river from Al-Deer district to the river's estuary at Al-Fao town during the period from January to December 2022. The samples were collected on a monthly basis using various fishing methods and tools. Three stations were chosen for the study: station 1 at Al-Deer distract, station 2 at Abu-Al-Kahseeb, and Station 3 at Al-Fao town. Some ecological parameters were measured: Water temperature, hydrogen ion, water transparency, and salinity concentration. A total of 60 fish species belonging to 48 genera and 32 families were caught affiliated with bony fishes (Osteichthyes class). The most abundant species was Carassius gibelio recorded at 15.00% of the total catch, followed by Oreochromis aureus w 13.48%, and Planiliza abu constituted 12.56% of the overall capture of fish. The diversity index (H) values ranged from 2.40 in January to 2.81 in May. The evenness index (J) values varied between 0.72 in December to 0.88 in January and March. The richness index (D) ranged from 2.67 in December to 4.51 in November. Resident species included 14 fish species, accounting for 78.64% of the total caught. Seasonal species comprised eight species, accounting for 14.44% of the total catch. Occasional fish species included 38 species, forming 6.92% of the total number of species. The present study concluded that salinity has a vital role in the distribution and spread of fish species, resulting in the composition of the fish assemblage; this was demonstrated in the three study sites if the composition between them differed, and there is a clear gradient in the composition of the fish population from the top of the river towards the sea.