STUDIES ON THE ENTERITIS OF YEARLING GRASS CARP (CTENOPHARYNGODON IDELLUS)

The fact that Aeromonas punctata, a bacterium, causes enteritis of grass carp was reported decades ago, yet some suspicions against the pathogen have since been aroused, mainly because oral infections with the isolated strains of this bacterium were ineffective, The therapeutic effects of antibacterial medicines on diseased fish were also uncertain. Attempting to clarify the matters, further studies on this disease with yearling grass carp from Hunan and Hubei provinces were proceeded during 1964—1974. Oral infections were still unsuccessful, but more injurious strains were isolated from fish showing enteric symptom under natural condition and were identified to belong to the same species previousely reported. Other results in relation to fish enteritis were also obtained. They provided additional evidence that may further confirm the originally reported pathogen.Bacteriologically, the abundance of Aeromonas was found to be related to enteric disease. In lg fish hind-gut, the number of bacteria (mostly Aeromonas) was 108—1011 for diseased fish but 105—107 for normal ones. This relationship was even more prominent in fish blood, in which bacteria were normally absent, yet they increased to a considerable number when fish were suffering from enteritis.In serological and immunological aspects, it should be mentioned that bacteria derived from pond-fish with enteritis from natural source could be agglutinated by the antisera of pure strains of A. punctata, and vice versa.Treatments of enteric fish through diet containing antibacterial medicine, e. g. Furanzolidohe, were practiced and fairly good results have been obtained, provided that it was not complicated by hemorrhage.