The comparative histopathology as related to modes of attachment and scolex morphology, gross anatomy, host response and effects of the three caryophyllid cestodes Djombangia penetrans, Lytocestus indicus and L. parvulus was studied. Among them D. penetrans was found to be most pathogenic and elicited pronounced host reaction in the form of nodules and complete penetration of the intestine followed by L. indicus which caused shallow ulcers and mechanical obstruction, and L. parvulus caused denudation of the host intestinal tissues. Distribution of the cestodes in the intestine, multiple infections and niche widths as related to scolex morphology, modes of attachment as well as habitats are discussed. Photomicrographs of the species in situ, and of histopathology supplement the observations.
A comparison was made on the efficiency of oral and hyperosmotic vaccinations for the control of vibriosis in ayu (Plecoglossus altivelis), the equal dose of vaccine being used. 1) The formalin-killed vaccine adsorbed to compound feed was administrated to 350 fishes with a daily dose of 0.16 g/kg for 15 days. The challenge tests by V. anguillarum were carried out 30, 60 and 90 days after the vaccination. In the vaccinated groups, the survival rates after the challenge were 98, 86 and 78%, respectively; and in the control group, were 86, 52 and 50%, respectively. 2) Three hundreds and fifty fishes were dipped in 7% NaCl solution for 2 minutes, and then in vaccine solution for 3 minutes. In the vaccinated groups, the survival rates after the challenges that were started 30, 60 and 90 days after the vaccination were 100, 94 and 100%, respectively; and, in the control group, were 86, 52 and 50%, respectively. 3) From the experimental results on the consecutive usega of the vaccine solution, it may be concluded that the vaccine solution can be used for at least 3 times. These results showed us that the hyperosmotic vaccination makes it possible to treat over 3 times as much of ayu as oral one.
The streptococcal infection of cultured yellowtail, Seriola quinqueradiata, occured since 1974, resulted in serious damages to yellowtail productions every year. It is important for taking preventive methods against this disease to make clear the sources of infection. Fresh and frozen fishes used for diets in farms of the fish were examined to detect the causative bacteria. As the result, the causative bacteria, similar to Streptococcus faecalis and S. faecium, were isolated from several species of diet fishes. Yellowtails inoculated intraperitoneally with the isolates were killed with typical symptoms of this disease. The causative bacterium was found to be alive for over 6 months under low temperature, especially frozen condition. It was suggested that the contaminated diets with the causative bacteria may be one of the sources of infection and significant of the propagation of this disease.
Parasitological surveys were carried out of goldfish, Carassius auratus and carp, Cyprinus carpio from April, 1977 to Feburuary, 1979, and six species of Dactylogyrus (Monogenea, Dactylogyridae) were recovered; D. dulkeiti, D. formosus, D. anchoratus, D. baueri, D. intermedius and D. vastator from goldfish and D. anchoratus from carp. D. dulkeiti, D. formosus, D. anchoratus, D. baueri and D. intermedius are first recorded in Japan. Descriptions are given of the chitinous parts of the above species and also of the internal structures in D. dulkeiti and D. formosus. At present, six species of Dactylogyrus mentioned above from goldfish and three species (D. anchoratus, D. extensus and D. minutus) from carp have been reported in Japan.
During summer to witner in 1974, the streptococcal infection occurred among yellowtails cultured in coastal waters, and has given serious damages to yellowtail productions since then. The causative organism is a α-hemolytic Streptococcus and similar to Streptococcus faecalis and S. faecium (KUSUDA et al., 1976). In July 1976, however, another Streptococcus different from the above was isolated from yellowtails cultured at two fish farms in Wakayama Prefecture. Two isolates were found to be a β-hemolytic Streptococcus and agreed well with S. equisimilis in main characteristics (Table 6). The organium is also different from Streptococcus isolated from other fishes; rainbow trouts, eels, golden shiners, menhadens in hemolysis and tolerance tests. The strain isolated from the sample showing corneal opacity and pericarditis caused typical symptoms of this disease in pathogenecity tests. Therefore, present isolates may be responsible in part for this epizootic, too.
A large amount of red seabream Pagulus major (Temminck and Schlegel) larvae, 8.0-11.0 mm in total length, was killed by the parasitism of larval treamtode during a course of experimental culture in large scale. Many young numerous larvae trematode were found in the alimentary canal, and a few one in the urinary bladder, ureter and renal tubule of the diseased larvae of red seabream. The infection was presumably caused by the active feeding of red seabream larvae on the larval trematode libreated from their first intermediate host, top shell (Batillus cornutus).
Some bacterial diseases such as pseudotuberculosis (Pasteurella piscicida infection)and streptococcal infection(Streptococcus spp. infection)have been prevailing among cultured populations of yellowtail(Seriola quinqueradiata) in Japan. In the course of diagnostic works about bacterial infections of yellowtail in Tokushima Prefecture from 1976 to 1978, it was found that an additional bacterial disease, i.e. vibriosis, had been causing considerable mortalities for those three years in addition to the above-mentioned two diseases. The occurrences of the three diseases or the three pathogens in 1977 was demonstrated in a table, where it was shown that the vibriosis took place in the young fish (Body weight 3.7-42.5g) from late May to early July. The external sign of the vibriosis was characterized by opaque or congested eyes, eroded fins, darkened body color, and hemorrhagic or necrotic lesions on body surface and musculature. Vibrio sp. was isolated from these diseased fish, and submitted to characterization tests, agglutination tests with anti-V. anguillarum sera, and a pathogenicity test with healthy yellowtail. Putting all the results together., the etiological agent of the disease was identified as Vibrio anguillarum. This is the first record of V. anguillarum infection in yellowtail, though another vibriosis, the causative agent of which was reported as Vibrio sp. by KUSUDA (1965), has been known.