Significance of Flavobacterium diseases on salmonid farming in Chile Ruben Avendaño-Herrera 1 , Pedro Ilardi 2 , Jorge Fernández 1 1 Universidad Andrés Bello, Facultad de Ciencias Básicas, Departamento de Ciencias Básica. Santiago, Chile. 2 Laboratorio de Patología de Peces, Veterquímica, Santiago – Chile Correspondence: R. Avendaño-Herrera (reavendano@yahoo.com ) Abstract Chile is considered the second largest producer of farmed salmon in the world. This intensive fish farming has resulted in growing problems as bacterial diseases, and infections by Flavobacterium psychrophilum, Chryseobacterium species and other yellow-pigmented strains are considered to be one of the major problems in the freshwater stage in Chilean aquaculture where infections can result in 5 to 90% mortality rate of fingerlings, particularly in Atlantic salmon. The infections are frequently found in association with infectious pancreatic necrosis virus (IPNV), saprolegnia or parasitic fish pathogens as Ichthyophthirius multifilis, but the significance of these combinations is unclear. According to the distribution of the diagnosis informed by the laboratories showed that flavobacteriosis is the second pathology affecting salmon cultures, after Piscirickettsia salmonis. In the present article we review current knowledge on these bacterial pathogens, focusing on important aspects such as biochemical, serological and genetic characterization of the microorganisms. The diagnostic procedures employed in Chile are also discussed. We include the current status of prevention and control strategies, studies of virulence, and we attempt to highlight fruitful areas for continued research. 1. Introduction The intensive exploitation of salmonids is an activity of high economical importance in Chile, being this country considered the second largest producer of farmed salmon in the world with an estimated production of approximately 655 ton during the year 2007 (www.salmonchile.cl). The production mainly takes place in the South of the country and is dominated by the marine culture of Atlantic salmon (Salmo salar). However, the involvement of infectious salmon anaemia virus (ISAV) in a disease outbreak was officially verified in Atlantic salmon in mid-June 2007 (1), and to date 62.3% of Chilean marine sites is affected by the disease. Therefore, this intensification of fish farming has resulted in growing problems of infectious and/or non-infectious diseases, which cause significant economic losses due to mortalities of Atlantic salmon eggs, younger fish and post-smolt in seawater. Flavobacterium psychrophilum (formerly Cytophaga psychrophila and Flexibacter psychrophilus) is the causative agent of bacterial cold-water disease (BCWD) in a large number of freshwater fish species worldwide (2) and is of considerable economic significance to aquaculture producers. In Chile, F. psychrophilum was first isolated from a rainbow trout (Oncorhynchus mykiss) farm in 1993 (3); subsequently, this pathogen has been detected in other host species, such as Atlantic salmon (Salmo salar) and Coho salmon (Oncorhynchus kisutch) in different regions of the South of the country. It seems clear that movement of fish, in particularly fry, between farms located in different geographical areas has played an important role in the spreading of the disease across Chile.