Edwardsiella ictaluri (also known as enteric septicaemia of catfish, hole in the head disease, and ESC) is a member of the family Hafniaceae. The bacterium is a short, gram negative, pleomorphic rod with flagella. It causes the disease enteric septicaemia of catfish (ESC), which infects a variety of fish species (including many catfish species, knifefish and barbs). The bacteria can cause either acute septicaemia or chronic encephalitis in infected fish. Outbreaks normally occur in spring and autumn.