Detail of Grant Awarded Academic Researches
Study of the Distribution of Bacteria that Cause Disease in the Fish of the Tama River Habitat
(at that time)
|Lecturer, College of Bioresource Sciences, Nihon University|
From 2012 to 2013, 1631 fish of 32 species were caught by hook or net at 4 sites (lower basin, middle basin, tributary region, and upper basin) of the Tama River system, and an examination of the bacteria being carried and outbreak of diseases was implemented. For ayu (sweetfish), the result was that bacterial cold water disease (BCWD) or Edwardsiella ictaluri infection (enteric septicemia of catfish or ESC) were isolated, an outbreak of BCWD was confirmed in June and an outbreak of ESC in August. Also, Motile Aeromonad Disease causing bacteria were isolated mainly during the summer. Since ESC pathogenicity for fish species is not as well known as that for BCWD, infection experiments of bacterial strain isolated from ayu using the dipping method were carried out, confirming the pathogenicity for the strain isolated from presymptomatic ayu being as high as for the strain isolated from dead fish. In addition, pathogenicity was also indicated for Amur catfish and cut-tailed bagrid catfish, and in particular, cut-tailed bagrid catfish were shown to have a high pathogenicity in high water temperature environments. Although there were no verified outbreaks of ESC in the previous study implemented in 2011 in the Tama River, it was assumed that the increase in river water temperature due to a heat wave caused the outbreak of ESC in 2012 and 2013.
This research is the first report to clarify the status of colonization of bacteria that causes fish disease and the outbreak of disease covering the area from the clear waters of the river to the brackish estuary throughout the four seasons. We believe that the obtained results are applicable to the majority of medium to large rivers in Japan, and we plan to release the results to related organizations as fundamental information for enteric septicemia of catfish, of which Japan has experienced frequent outbreaks over the past several years. In regards to this disease, our results from the infection experiment showed that the bacteria colonizing presymptomatic fish have a high pathogenicity, and may be able to infect fish other than ayu in the Tama River habitat. We tend to look toward waste water or river bank protection improvements as causes of diminished fishery resources in rivers, but this research suggests that fish disease may be another cause, and we must promote related educational activities and further analysis of pathogenicity.
Hisato Takeuchi, Graduate Student, Nihon University
Motoyuki Hiratsuka, Graduate Student, Nihon University
Hiroki Oinuma, Undergraduate Student, Nihon University
Yoshiyuki Umino, Undergraduate Student, Nihon University
Daiki Nakano, Undergraduate Student, Nihon University
|Full Text||Download (Japanese Only)|