The Emergence of Pathogenic Bacteria in Coldwater Ichthyofauna: A Review

Pathogenic bacteria are the most common causes of serious illness outbreaks in wild and farmed coldwater fish around the world, and they have socioeconomic consequences. Pathogenic bacteria can also cause zoonotic illnesses and infection in both humans and fish. Coldwater fisheries that are susceptible to bacterial infections include Schizothorax, Rainbow trout, and Salmonids. At temperatures ranging from 5 to 14°C, coldwater bacterial pathogens proliferate and cause epidemics. Furunculosis, motile aeromonas septicemia, coldwater illness, columnaris, bacterial gill disease, vibriosis, edwardsiellosis, and pseudomonasis are the most common gram-negative diseases in coldwater fisheries. A few gram-positive bacterial pathogens, Streptococcus agalactiae, produced streptococcosis in hill stream fisheries, while Lactococcus garvieae caused lactococcosis. The bacteria that cause disease in coldwater fisheries are mainly opportunistic pathogens while few are obligate pathogens. This review discusses the bacterial agents, and diseases caused by them with emphasis on the bacterium-host interactions by compiling some published literature scattered over the past decades.