Black gill disease of pond-cultured kuruma prawn, Penaeus japonicus was first reported by EGUSA and UEDA (1972). They demonstrated that a fungus belonged to the genus Fusarium was the causative agent and gave the fungus a temporary designation, BG-Fusarium. Since their report the disease has often broken out among pond cultured kuruma prawn in various districts. The present authors investigated a taxonomical position of the BG-Fusarium isolated from gill lesions of kuruma prawn with black gill disease. As the result, the BG-Fusarium was identified as Fusarium solani according to BOOTH (1971, 1977) from the characteristics of the fungus on Potato Sucrose Agar. The number of fungal elements (conidia, chlamydospore, mycelium, etc.) per g of wet sand in ponds in which black gill disease had broken out were 3.0×10-8.0×102, among which number of fungus as element of BG-Fusarium were 2.0×10-8.0×102. BG-Fusarium was not isolated from the sand of ponds in which the disease was not occurred. This fact may suggest that the sources of infection lie in the sand of culturing ponds. BG-Fusarium was also isolated from the bottom sand of ponds which were emptied for 2 months. This fact suggested that BG-Fusarium was capable of surviving for long time in wet sand.
Results of experiments on the effect of temperature on the survival of conidia of BG-Fusarium in sterile sea water and sterile distilled water suggested that the organism can survive in each water for prolonged of time. The survival rate was about 80% even after 140 days in each water at 10 to 30°C. Conidia of BG-Fusarium in sterile sea water, however, failed to survive 140 and 105 days when they were held at 5°C and 37°C, respectively. On the contrary those in sterile distilled water failed to survive 70 and 21 days when they were held at 5°C and 37°C, respectively. The BG-Fusarium grew well on Sabouraud dextrose agar containing 0 to 0.5% NaCl, and did up to 10% NaCl, but failed to grow at 12% NaCl. It grew in Sabouraud dextrose broth at the pH range from 4 to 11. All the BG-Fusarium strains and F. solani F-21 (plant pathogen) were resistant to cycloheximide. Two strains, F-22 and F-23 of F. solani, however, were susceptibile to the antibiotic. Malachite green completely inhibited mycelial growth at 6.3 ppm. Sodium dichloroisocyanurate was found to kill the conidia of BG-Fusarium at a concentration of 6.2 ppm as active ingredient.
A gram-negative filamentous bacterium was isolated from the gills of salmonids, Salmo gairdneri and Oncorhynchus masou, with gill disease. The isolates did not show gliding movement. Growth on Cytophaga agar was pigmented yellow. Colonies were small, translucent, smooth and entire. There was no growth on nutrient agar and meat-extract broth. Acid was produced from glucose and sucrose. Growth was best at 15-20°C. Attempts succeeded in transmitting bacterial gill disease to fingerling trout by adding pure cultures of the bacterium in aquariums. The experimentlly infected gills showed essentially the same symptoms as seen in naturally occurred gill disease.
The authors histopathologically examined melanoma found on the head of a three-year-old rainbow trout(Salmo gairdneri)caught in Samegai Trout Culture Station in 1974. A neoplastic mass was observed to be a protuberance of black color with papillate surface. Histopathologically, the tumor arose from the dermal loose connective tissue. It consisted of a considerable number of mature melanocytes and immature ones extending in all directions as a parenchyma and of a large amount of thin collagenous fibers as a stroma. Metastatic production was not observed in this case.
Though ulcer disease of goldfish has been thought to be of an infectious nature, the etiological agent has not yet been isolated in Japan. Intradermal inoculation of skin materials taken from affected skin areas of diseased goldfish can induce ulcerative lesions at the site of inoculation, but the progress of the lesions is mostly somewhat different from that observed in natural outbreaks. In this study an attempt was made to develop the method for experimentally inducing the same skin lesions as those in naturally occurred ulcer disease. A scale was pulled out from a congested part surrounding an ulcerative lesion and immediately inserted beneath a scale of a healthy fish. The scale inserted was removed after various periods of time. As a result ulcer lesions were produced in 70 to 100 percent of the inoculated fish and the external appearance and the progress of the lesions were the same as those in naturally diseased fish. One minute insertion was satisfactory. This method may be useful for the study of ulcer disease, in particular of its treatment.
Suspensions of spores of Glugea plecoglossi in distilled water or 0.85% NaCl solution (about 107-108 spores per ml) were injected subcutaneously (0.05 ml) and intraperitoneally (0.1 ml) into Ayu (Plecoglossus altivelis) (9-15 g). Fish injected with distilled water or 0.85% NaCl solution were used for controls. The experimental and control fish were kept at about 19-20°C after injection. After 22 to 35 days all fish were sacrificed and examined by the naked eye for the presence of “Glugea cysts” not only in the site of inoculation but also in the other parts of the body. The results were as follows. In almost all fish inoculated with spores subcutaneously many Glugea cysts had been produced at the site of inoculation. Besides, cysts were observed in internal organs such as pyloric caeca, peritoneum, gonads, adipose tissue and spleen. In the fish received spores intraperitoneally many cysts were observed to be formed on pyloric caeca, peritoneum, gonads, adipose tissue, liver, heart and spleen. In addition, cysts were found in subcutaneous tissue and peripheral muscle tissue in various part of the trunk. This spore injection method seems to be useful for the studies not only on the pathology, and treatment of microsporidioses but also on the life cycle and host range of microsporidia.
In November, 1975, a clove worm was detected in the intestines of carp, Cyprinus carpio, which were collected in an irrigation pond farm in Gunma prefecture. They were six month old and 12.5-14.7 cm in body length. The worm was never found in carp which harbored another cestode, Bothriocephalus opsariichthydis YAMAGUTI. A monthly examination revealed that the number of the worm decreased rapidly after November and no worm could be detected from January to May. This suggested that the worm can not survive the winter. Ten worms fixed in 70% alcohol, stained with HE and mounted in balsam were observed:Body slender, 11.0-16.2 mm long by 0.8-2.4 mm wide; Scolex undifferentiated, conic or turncate, 1.2-2.7 mm wide; Cirrus pouch well developed, 0.52-0.68 mm long by 0.40-0.56 mm wide;Uterine coils between cirrus pouch and H-shaped ovary; Postovarian vitellaria medullary; Egg elliptical with thin shell, 44-50×22-34μ. The present worm was similar to the two species of the genus Khawia (Cestodaria:Caryophyllidae) in shape and size, K.japonensis (YAMAGUTI, 1934) YAMAGUTI, 1959 and K. sinensis HSÜ, 1935. These two species are distinguished only by the size of eggs, that is, the eggs of the former have been reported to be 48-57×36-42μ and those of the latter 42-48×25-30μ. Based on the egg size the present clove worm was identified as K. sinensis.