Compositional Change in Fish Assemblage Structure in the Shatt Al-Arab River, Iraq

Abstract

Shatt Al-Arab River suffered from deterioration in water quality due to seawater intrusion as a result of the decline in rate of discharge of freshwater during the recent years. Therefore, the fish assemblage structure in the river was assessed using taxonomic and functional metrics of assemblage structure during the period from November 2015 to October 2016. Fish were sampled monthly by different fishing gears including gill nets, cast net and electro-fishing from three sites on the river.  The fish assemblage consisted of 111 fish species representing 50 families belong to Osteichthyes except three relate to Chondrichthyes. The fish fauna comprised 15 native, 13 exotic and 83 marine species. The most abundant species were Carassius auratus (13.24%), Oreochromis aureus (12.58%) and Planiliza  klunzingeri (10.56%). The dominance value (D3) was 63.4%. The resident species formed 36.0%, occasional species 55.9% and seasonal species 8.1% of the total number of fish species. Fish diversity index ranged from 1.62 to 2.22, richness from 2.23 to 4.63 and evenness from 0.40 to 0.64. Canonical correspondence analysis indicated that water temperature and salinity correlated positively with the number of species. The results revealed that the fish assemblage in the river was clearly shifted in the number of species, the percents of exotic and marine species and the dominancy species compared with the previous status.