The class Flavobacteriia is composed of a single order of environmental bacteria. Flavobacteriia are a group of commensal bacteria and opportunistic pathogens. Flavobacterium psychrophilum causes the septicemic diseases rainbow trout fry syndrome and bacterial cold water disease. According to Bernardet et al., Flavobacteriia are gram-negative aerobic rods, 2–5 µm long, 0.3–0.5 µm wide, with rounded or tapered ends that are motile by gliding, yellow (cream to orange) colonies on agar, decompose several polysaccharides but not cellulose, G+C contents of 32–37 %, and are widely distributed in soil and freshwater habitats. The type species is F. aquatile.