Morphological observations were made on eggs and coracidia of Callotetrarhynchus nipponica (a tentative name proposed by us) and the hatching rates of coracidia were examined under different environmental conditions. Fertilized eggs of C.nipponica are ovoid with opercula and 4248×2734μ in size. Unpressed living specimens of coracidia liberated from eggs are imperfect globular bodies of 3035×2833μ in size, with long cilia of 1015μ over the entire surface, though they appear disk-shaped under a cover glass. The embryonic hooks observed in coracidia are 1012μ in length. Eggs which were mostly in the blastula stage were placed in 10 dishes filled with filtrated sea water. Out of the 10 dishes 6 were set under the window at room temperature (10.720.3°C). The remaining 2 were kept under a fluorescent lump throughout the experiment and the other 2 were covered with black envelops. These 4 dishes were incubated at 25.0±1.0°C. Three days after spawning, coracidia were formed in the operculated eggs in all dishes and, after 4 to 6 days, the liberation of the coracidia were observed. The hatching rate of coracidia was independent of light and temperature and was 95.1% in average of the 10 dishes at 7 days after spawning.
In 14 previous papers, we reported on various stages of the life cycle of Callotetrarhynchus nipponica (a tentative name proposed by us). That is: Procercus with a cephalic organ, “borer” and scolex anlage, is parasitic on the abdominal body cavity ofEngraulis japonica; Procercus developes into Plerocercus with the scolex in the body cavity ofSeriola quinqueradiata or some other teleosts; Adult are found in the valvular intestine of Scoliodon walbeemi, a kind of requiem shark; Oraly administered plerocercus can develope into the adult in the valvular intestine ofTriakis scyllia under experimental conditions; Fertilized eggs are spawned from the gravid proglottides when the latter escape from the intestine into the sea; Ciliated coracidia liberate from theoperculated eggs. In the present study efforts were made to clarify the processes of the development from coracidium to procercus. The results were as follows;1)9, 066 copepods of 15 genera collected from 4 different areas in the Bungo Channel and its adjacent seas were examined for stages following the coracidium. The result was negative.2)Copepods of 11 genera, Cladocera and zoea staged larvae, 1, 728 in total, collected from the stomachs of 150 Engraulis japonica(spring hatched group and 37 months old)caught in the Uwa sea were similarly examined.The result was negative, too.3)About 10 thousands coracidia were made in contact with 106 Tigriopus japonicus and the other 87 copepods of 9 species in beakers contained 1, 000 ml of sea water. Coracidia were not ingested by the copepods within 5 days. 4)About 800Engraulis japonica of 6.211.8cm in body length caught in the Sagami bay and 5 Triakisscyllia of 53.679.5cm in total length which had been artificially infected with the adults of C. nipponica were kept in the same aquarium. 325 anchovies were examined for procercus through 50 days with negative results. Consequently the complete life cycle ofC. nipponica is still unknown, but we believe that our studies on the present species may give leading informations concerning the life cycle of Trypanorhyncha.
During the late spring to the midsummer of 1971, an epizootic occurred among pondcultured Ayu, Plecoglossus altivelis, in Tokushima Prefecture. The disease was characterized by the diposition of white spots on the liver. The etiological agent was isolated from white spots on the liver and the kidney. The organisms were gram-negative, non-motile, polarly stained rods, and usually 1.0 to 3.0 by 0.3 to 0.5μ in size. On BHI agar, colonies doveloped within 24 hours at 25°C, and were uniformly round 1 mm or less in diameter. Growth was observed on MACCONKEY agar, ENDO agar, and ARAKAWA modified agar. Glucose, furactose, galactose, saccharose, maltose, dextrin, cellobiose, and salacin were fermented anaerogenically by the organism, whereas arabinose, xylose, mannose, trehalose, mannitol, and sorbitol were not attacked. Indole, H2S, acetyl methyl carbinol, methyl red, nitrate reduction were negative. Oxidase and catalase were positive. Because of its polar-staining and physiological reactions, the organism fits best in the genus Pasteurella. The isolate was found to be not identical to any formally established species. We propose that it be identified as Pasteurella plecoglosacida sp. nov.
In July, 1972, branchiomycosis broke out among eels(Anguilla japonica) in a eel-culturing pond at Saijo, Ehime Pref., Japan, and caused considerable mortality.The causative agent was closely related to Branchiomyces sanguinis PLEHN.The width of the hyphae measured from 10 to 30 μThe spores in the hyphae were from 4.5 to 7μ in diameter.The hyphae were located in the tissues of the gill filaments, not growing from the gills outwards.