Humphreysia hoi sp. nov. is described based on the specimens collected from the gill filaments of Parapercis sexfasciata (Temminck & Schlegel), caught in Kojima Bay, Japan. It can be easily differentiated from the type-species, H. floreata Leigh-Sharpe, 1934, on the body shape, first antenna, and oral appendages. The male is described for the first time in the genus, its claw-less maxilliped is unique in the Chondracanthidae.
Infectious pancreatic necrosis virus (IPNV) persistence in carrier brook trout and persistently infected cell lines was examined. Viral persistence in vivo and in vitro was characterized by a fluctuating release of infectious virus (<101.6 to 106.0 TCID50/g or ml) in the absence of external signs or cytopathic effects. Infectious center assays indicated that virus was produced by less than 1% of the cell population of persistently infected lines and carrier trout kidney tissues. Antibody was not involved in viral persistence in vitro and its role in vivo was not clear. Interferon was not detected in the two persistently infected lines or in the sera of carrier trout examined in this study. Viral replication in one of these cell lines was controlled instead by the presence of defective interfering (DI) virus which had the capability of interfering with infectious virus multiplication and viral-induced cell lysis. The similarities of viral persistence in cell lines and carrier brook trout suggested that the same virus host cell interactions occur in vitro and in vivo.
The epidemic of ulcer disease of goldfish is in the spring. The condition is first observed in April and the diseased fish increase in number until June or July. Thereafter, the condition turns to cure till autumn. These facts suggests that the water temperature plays an important role in the etiology of this disease. In the present study, two experiments were performed. In experiment 1, infection was artificially induced at different water temperatures from 2.5 to 30.0°C. The lesions could be induced within the range of temperature from 7.5 to 30.0°C. Incidence of the lesion exceeded more than 90% from 20.0 to 27.5°C. The terminal stage of the lesion was observed after 5 days at 25-27.5°C and 14 days at 12.5°C, respectively. In experiment 2, diseased fish collected from culture ponds were kept in the tanks with water of different temperatures from 20.0 to 30.0°C and no antibacterial agents to observe the recovery pro-cess. The rapid recovery of the lesions was observed at the temperatures more than 27.5°C. From these results, it is conceivable that the harmful temperature for the ulcer disease of goldfish is about 18 to 23°C, for within it the disease infection was easily and ulcer formation was much faster and not recovery.
Median lethal doses (LD50) of Aeromonas salmonicida on Amago salmon, Oncorhynchus rhodurus were studied by three different infection routes. LD50 of the bacteria on Amago salmon by intramuscular injection, intraperitoneal injection and bathing method (water-borne injection) were estimated as 4.3-5.1 × 100 CFU/fish, 3.0-4.5 × 103 CFU/fish and 2.2-2.7 × 106 CFU/ml, respectively. The fluctuations of LD50 obtained in the each duplicate experiments were ignorable. This suggests the advantage of using genetic isolated stocks of fish for the experimental animal.
A microsporidian species which invades the trunk muscle of yellowtail juveniles (Seriola quinqueradiata) and causes “Beko” disease was studied. The parasites appeared as multiform masses in cross sections of the muscle and usually elongated masses in longitudinal sections. The masses were bounded externally by a host-produced fibrous membrane. Almost all the parasites clearly represented stages in the sporulation sequence. Sporogony was believed to occur by multiple fission of sporogonial plasmodia. Sporocyst, sporogony vacuole and pansporoblast membrane were absent. The diplocaryon was not confirmed in any sporulation stage. Fresh spores were ovoid and measured 2.9-3.7×1.9-2.4 μm and had a coiled polar tube within the spore membrane. Extruded polar tubes were 44-52 μm in length. This species could not be classified in any established genus and therefore it seemed appropriate to place it provisionally in the collecting group Microsporidium. The name M. seriolae was proposed. The specific name refers to the genus name of the host.
“Beko” disease whose causative agent is Pleistophora anguillarum is well known in eel culture. There are, however, few reports on chemotherapy of the microsporidiosis in fishes. The present study was undertaken to induce Pleistophora infection experimentally and examine the effect of fumagillin as a chemotherapeutic agent. Experimental infection was tried by inoculating orally Pleistophora spores into juvenile eels or immersing them in water suspension of the fresh spores. Both methods were successful in inducing the same symptom as that of naturally-occurring diseased fish. Early schizonts, cysts in the trunk muscle, and whitish lesions on the body surface were observed around 10, 20, and 25 days after inoculation, respectively. In oral infection, the whitish lesions developed mainly on the body surface around the abdomen. In the immersing infection, on the other hand, they were scattered over the whole body. These results and the histological investigations suggest that the parasite at early stages reaches the musculature via the gut wall and peritoneal fluid in oral infection, and via the skin in immersion, rather than via the blood vascular system. From another experiment, it was found that Pleistophora infection was very weak at low temperature such as 14°C. Fumagillin was found to have prophylactic effect on these experimental infections by oral or immersed administration immediately after inoculation.
Efficacy of oral vaccination for control of streptococcal disease in cultured yellowtail was studied. The bacterin, the formalin-killed cells of Streptococcus sp., as the etiological agent of this disease, was used. This bacterin was administrated 1, 2, 4, 8, 16 times at a level of 5 mg dry weight per fish per day, and 8, 12 times at a level of 20 mg wet weight per fish per day. About a week after the last vaccination, fish were challenged for the estimate of efficacy of oral vaccination. Duration of oral vaccination effect was also tested. Dry bacterin was fed 2, 4, 8 times, and about 1, 2, 3, 4 weeks after the first vaccination, fish were challenged for the estimate of oral vaccination effect. Both dry and wet bacterin were effective, and the efficacy became more active with an increase in frequency of oral vaccination. But antibody in the blood was not detected. Duration of oral vaccination effect was very short. That effect was prolonged for only 2 weeks after the last vaccination. In order to compare with oral vaccination, efficacies of hyperosmotic infiltration and intraperitoneal injection for control of this disease were also studied. Hyperosmotic infiltration was more effective than oral vaccination. Intraperitoneal injection was the best method of three experimented.
At the middle of July, 1979, a bacterial infection occurred in a young population of black seabream (Acanthopagrus schlegeli) cultured in three tanks. These fish had been reared in sea water tanks since they hatched out at the end of May. The epizootic broke out in all tanks, lasted about one month, and killed 3300 fish out of 8000 (41% mortality). The causative agent isolated from liver or kidney materials of all the fish examined was identified as Pasteurella piscicida by comparing the characteristics of the present isolates with that of the isolates from black seabream by MUROGA et al. (1977) The source of the infection was thought to be the sea water supplied to the tanks because of the frequent occurrence of Pseudotuberculosis (P. piscicida infection) in yellowtail (Seriola quinqueradiata) in adjacent area.
Although vibrioses caused by Vibrio parahaemolyticus, V. alginolyticus and some other unnamed vibrios have been reported in reared juvenile or farmed red sea-bream (Pagrus major), V. anguillarum infection of the fish species has never been reported so far in Japan. In June 1981, V. anguillarum was isolated from reared juvenile red sea-bream (average body length 17 mm) às a cause of an epidemic outbreak in a hatchery. At the same time, other two strains which had been isolated from the same fish species at another hatchery in 1978 were also identified as V. anguillarum. The infection caused by the organism seems to be one of the significant diseases in artificial seed production of red sea-bream.