Brown Pigment-producing Isolates of <i>Flavobacterium psychrophilum</i> from Ayu <i>Plecoglossus altivelis</i>

Isolates of Flavobacterium psychrophilum that produce brown pigments were obtained from ayu Plecoglossus altivelis at a farm in Hiroshima Prefecture, Japan in 2014 and 2015. In 2016, similar bacteria were isolated from ayu caught in a river in a different area. Eleven isolates producing brown pigments were obtained from both farmed and riverine ayu, and PCR-RFLP revealed the same A/S/QS/C genotype in all isolates. Infection experiments conducted with two isolates from farmed and riverine ayu revealed that both isolates had a similar LD50 and relatively weak pathogenicity. ​However, the property of this brown pigment remains unknown and requires further investigation.