One hundred sixteen isolates of Edwardsiella tarda were collected from the United States and Taiwan were biochemically characterized. This species is basically homogenous and has limited substrate utilization capacities. Taiwan isolates differ from the United States isolates in some respects (i.e. mannitol fermentation, motility, hydrogen sulfide production, gas production, and chondroitin sulfate degradation) particulary when incubated at 42°C.
An infectious disease caused by a β-hemolytic Streptococcus has been observed in several freshwater and marine fishes, especially in ayu(Plecoglossus altivelis)cultured in commercial farms. In a previous paper, the biochemical characteristics of 5 strains isolated from diseased ayu and amago(Oncorhynchus rhodurus var. macrostomus)were reported. In the present paper, physiological characteristics and pathogenicity of the isolates from ayu are described. 1)Effects of temperature, sodium chloride and pH on the growth of the organism:It grew at temperature20-37°C(optimum range 25-30°C, at NaCl 0-3%(optimum range 0-1%)and at pH 6-8(optimum7). 2)Survival in waters:It perished within a day in freshwater, and within 3 days in sea water.But it survived over 8 days in 0.01%yeast extract added distilled water. 3)Pathogenicity by intraperitoneal injection:It showed high pathogenicity to ayu and amago, and weak pathogenicity to tilapia(Tilapia nilotica), yellow tail(Seriola quinqueradiata) and seabream(Pagrus major).But it was not pathogenic to carp(Cyprinus carpio)or black seabream(Acanthopagrus schlegeli).
Descriptions and identifications are given of two new blood flukes from the vascular system of a marine fish, Seriola purpurascens, cultured intensively on a Pacific coast of Shikoku Island, Japan. The two trematodes belong to the genus Paradeontacylix (Sanguinicolidae). P.grandispinus sp. nov., about 2.0-3.3 mm in body length, resembles P. sanguinicoloides MCINTOSH, 1934 in general morphology, but can be separated from it in the shape of the spines at the posterior end of body and in the number of testes. P. kampachi sp. nov., about 4.7-8.1 mm long, is most similar to P.odhneri (LAYMAN, 1930), but different from it in the relative position of ovary.
The ratio of GC composition and DNA-DNA homology among the representative strains of each phenon and between the five phenons and six single member-clusters, as described in a previous report (TAJIMA et al., 1985b), were examined. All of the strains tested exhibited GC values in a range from 43 to 46 %. From these results, the strains used were reconfirmed as Vibrio. The DNA of reference strains (phenon I: V-7 NCMB 6, V-116 NCMB 407, phenon II: V-105 NOAA V-1669) of phenon I (V. anguillarum) and phenon II (Vibrio sp.) were genetically homologous with isolates belonging to the corresponding phenons, while they were very distantly related to the isolates belonging to phenons III, IV, V and other single member-clusters. A homology of 77-80% of DNA for phenon II isolates against the reference DNA (V-7 NCMB 6) of phenon I was comparable to that of DNA for phenon I isolates. According to the numerical taxonomy carried out previously, we considered phenon I and phenon II to be different species due to similarities of less than 57 %, but the present results of the DNA-DNA homology indicated that these two phenons probably belong to the same species.
Two species of streptococci were isolated from the brain of the vertebral deformed yellowtail cultured in Lake Hamana, Shizuoka Prefecture. One species was α-hemolytic and the other was non-hemolytic. The α-hemolytic isolates were identified as the well-known etiological agent of streptococcicosis in yellowtail. The non-hemolytic Streptococcus did not grow in media containing 0.1 % methylene blue milk, 6.5 % NaCl, 10% and 40% bile. Growth at pH 9.6 was positive, but growth at 10°C and 45°C, and heat tolerance (60°C for 30 min) were negative. Final pH in glucose broth was 4.5. The isolate did not hydrolyze gelatin, starch, esculin and arginine, but hydrolyzed sodium hippurate. This non-hemolytic Streptococcus was not classified as any of Lancefield's serological groups. This Streptococcus was placed in the Streptococcus group I, B because growth at 10°C and 45°C were negative and hydrolysis of sodium hippurate was positive. The bacterium, however, was not identical in biochemical characteristics with any formerly established species of the genus Streptococcus. The non-hemolytic Streptococcus showed fatal pathogenicity for yellowtail by intraperitoneal injection. Further work is required to explain between the isolate and the vertebral deformity.
During a one year period, 355 net pen cultured yellowtail (Seriola quinqueradiata) and amberjack (Seriola dumerili) mortalities were examined for bacterial infections. A comparison of detection of pathogenic bacteria by direct fluorescent antibody bechnique (FAT) and media culture was performed. Fluorescein labeled rabbit immunoglobulin G (IgG : Fl) was prepared against Streptococcus sp., Pasteurella piscicida, Nocardia kampachi and Vibrio anguillarum. Heat fixed smears of kidney from each mortality were stained with each one of the IgG: Fl preparations and examined using fluorescent microscopy. In addition, kidney samples were inoculated on brain heart infusion agar and Ogawa media. From the 355 mortalities, FAT detected 485 infections as compared to 347 by culture. The respective numbers of fish that bacteria were detected by method were (bacteria, by FAT, by culture): Streptococcus sp., 89, 55; P. piscicida, 293, 269; N. kampachi, 91, 17; and V. anguillarum, 12, 7. The FAT diagnosed 127 mixed infections as compared to 20 by culture. Three mortalities were not infected by FAT (confirmed by culture) as compared to 28 mortalities where no infection was apparent by culture. The FAT proved to be a rapid (1 h), effective and powerful method for diagnosis of bacterial infection, especially of mixed infection which the culture method frequently failed to detect.
The cidal effects of ultraviolet (U.V.) irradiation on fish pathogenic viruses were examined. Basic experiments were carried out to determine the usefulness of a U.V.-water treatment unit for the disinfection of IHNV and OMV. The results obtained are summarized as follows: 1. The disinfectant effect of U.V. on 6 species of 7 strains of cell free fish pathogenic viruses was examined. IHNV, OMV, CCV and H. salmonis were found to be sensitive to U.V. and the 99% or more reduction of their infectivity (ID99)was measured to 1.0-3.0×103μW·sec/cm2. Susceptibility of IPNV and CSV was found to be low and the ID99 was measured to 1.0-1.5 × 105μW·sec/cm2. 2. U.V. treatment of less than 16.7l/min flow rate that is equivalent to more than 7.6×104μW·sec/cm2 U.V. dosage, is an effective means of disinfecting the 100 TCID50/ml of IHNV and OMV suspended in dechrolinated city water.