Tenacibaculum infection (previously known as flexibacteriosis) represents one of the first bacterial conditions being reported in marine aquaculture in a large range of species including flat fish like sole (Solea solea) and turbot (Schopthalmus maximus); and finfish, namely sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata). The disease is associated to the infection with bacteria from the genus Tenacibaculum spp. In some marine areas or in recirculation systems, the infection severely threatens production with mortalities rising over 30%. Prevalence and intensity of the infections vary in relation to environmental parameters and zootechnical/rearing conditions and are influenced with factors such as handling, mechanical lesions or stress and interfering parasitic infestations. Many studies support the hypothesis of Tenacibaculum spp. as an opportunistic pathogen that primarily causes extensive skin lesions and gill abrasion, and subsequent systemic infections. Clinical signs of tenacibaculosis are variable according to fish species and type of infection. Affected fish show loss of appetite, become lethargic and show skin lesions around the eyes, on the head on the body surface described like ulcers, necrosis, eroded mouth, frayed fins and tail rot, and sometimes necrosis of the gills and eyes.