Abstract:Aim of this investigation is to provide the general information about prevalence of members of Enterobacteriaceae in horse mackerel (Trachurus trachurus) sold in open public markets in Istanbul, Turkey. Horse mackerel were randomly selected and collected in warm and cold seasons of the year. Purchased samples were kept in sterile insulated bags with ice and transported to the laboratory for microbiological analyses. Citrobacter spp. showed highest prevalence (45.56%), followed by Proteus mirabilis (22.62%), Proteus vulgaris (9.17%) and Escherichia coli (7.64%). The other isolates were Shigella sonnei (4.28%), Shigella dysenteria (3.36%), Salmonella Typhimurium (1.83%), Salmonella Paratyphi A (1.52%), Klebsiella pneumoniae (1.22%), Klebsiella oxytoca (1.22%), Enterobacter aerogenes (0.91%) and Enterobacter cloacae (0.61%). The percentages of the isolates, obtained in spring and autumn, were also compared. The Citrobacter spp., P. mirabilis and P. vulgaris were the dominantly isolated species, during spring season. P. mirabilis and Citrobacter spp. were also dominant in autumn. However, numbers and percentages of isolated pathogens (E. coli, S. sonnei, S. Dysenteriae, S. Typhimurium and S. Paratyphi A) were much more in autumn than that of spring. Since samples are sold without any chilling treatment in public markets, air temperature might be the reason of higher pathogen isolation in autumn. It is essential to implement cold chain as well as to prevent secondary contamination and to improve quality control.