Studies on Red Spot Disease of Pond-cultured Eels-IV

Physiological characteristics of the causative bacterium, Pseudomonas anguilliseptica

Abstract

As previously reported (MUROGA et al. 1973), red spot disease (Pseudomonas anguilliseptica infection of cultured eels) prevails in brackish-water ponds when the water temperature is below 20°C, and ceases when it rises to 27°C.
In this paper, physiological characteristics of the causative bacterium, P. anguilliseptica were investigated, and the results were discussed with respect to the epizootiological facts described above. The experimental results and conclusions are summerized as follows.
1) Effects of pH, NaCl and temperature on the growth of the organism: It grew in nutrient broth at pH 5.3-9.7 (Optimum range 7-9), at NaCl 0-4% (Optimum 0.5-1%) and at temperatures from 5°C to 30°C (Optimum 15-20°C).
2) Effects of NaCl or chlorinity on the survival of the organism: The period of survival was prolonged with the increase in concentration of NaCl or chlorinity, and the organism survived more than 200 days in sea water and in diluted sea waters (Cl≥1.9‰). This nature of the organism is considered to be closely related to the fact that the disease prevails not in freshwater ponds but in brackish-water ponds.
3) Effects of temperature on the survival and the motility of the organism: The organism survived in diluted sea water (Cl 5.6‰) more than 40 days at 27°C and below, but it perished within 7 days at 30°C and above. The motility of the organism was gradually inactivated by increasing incubation temperature, and was poor above 25°C.
4) The above-mentioned nature of the organism against temperature is considered to be the main cause of the temperature-dependence of the epizootic.