The aim of this study was to investigate the prevalence of columnaris disease in wild sharptooth catfish, Clarias gariepinus, in Upper Egypt. Columnaris was detected in 7 (4.86%) fish out of the 144 fish collected indicating light infection. The main signs observed on fish were paleness and sloughing of gill filaments, in addition to skin erosions and fin rot that were seen on some specimens. No specific pattern was detected in weight susceptibility of sharptooth catfish to columnaris. Prevalence of the disease was highest in autumn than in other seasons of the year. Pathogenicity of Flavobacterium columnare isolated in the present study was investigated through an immersion challenge. Fish groups to be challenged were either subjected to skin or gill scarification or remained un-scarified. All challenged fish were immersed in 3.5X10⁷ colony forming units/ml of F. columnare challenge suspension. Clinical signs as loss of appetite and sluggish movement began to appear on fish 48 hours post challenge, while respiratory manifestations and skin erosions appeared later. Two fish died out of the group that had skin scarification. It was interesting to notice that fish challenged through immersion without scarification did not develop typical signs of infection. The antibiogram of F. columnare was also investigated where it was highly sensitive to cefotaxim, ciprofloxacin and ofloxacin, but resistant to cephradine, while moderately to less sensitive to trimethoprim-sulfamethoxazole, E-moxclav, colistin, and flummox.