Seasonal Fluctuations of Flexibacter sp. the Causative Bacterium of Spotting Disease of Sea Urchin Strongylocentrotus intermedius in the Culturing Facilities and Coastal Area

Abstract

An ecological survey on the causative bacterium, Flexibacter sp. of spotting disease of sea urchin Strongylocentrotus intermedius was carried out for 14-months at monthly intervals from September, 1993 at Shakotan-Cho Fisheries Breeding Center and at coastal area near the Breeding Center in Bikuni, Hokkaido, Japan. The causative bacterium of spotting disease was not detected in any samples from winter season to early summer season until seawater temperature reached at 20°C. But the bacterium was detected in various samples from the Breeding Center and of wild sea urchins and seaweed (Codium fragile) at stations 1 and 2 in the mid August when seawater temperature was 20°C or higher. Spotting disease occurred within a few days after the first detection of the bacterium. After ceasing of the disease the bacterium was continuously detected from some samples in the Breeding Center from September to December when the seawater temperature was declining. From these results, it is speculated that the causative bacterium proliferated in natural seawater at above 20°C and entered into rearing tanks through supplied seawater and then the disease was caused by bacterial attaching and proliferating on surfaces of sea urchins.