2025 Volume 60 Issue 1 Pages 16-19
A mass mortality event with a mortality rate of approximately 30% occurred among juvenile ayu Plecoglossus altivelis in a hatchery in Japan that uses pure seawater for rearing. Bacteria isolated from the kidneys of dead fish were identified as Tenacibaculum maritimum using 16S rRNA sequencing and PCR analyses. Immersion infection experiments using this isolate confirmed a high mortality rate in ayu at a bacterial concentration of approximately 106 CFU/mL. Rearing affected ayu in half-strength seawater for 7 days significantly reduced deaths in the hatchery, and this effect was reproduced in the infection experiment. It was shown that rearing infected fish in half-strength seawater effectively treated this condition.
