The preceding papers(MUROGA et al., 1976 a, b)dealt with the biochemical characteristics, taxonomical status, physiological characters and pathogenicity of Vibrio sp. isolated from a new eel vibriosis. In this paper the effect of NaCl concentrations of cultrue media on the NaCl tolerance and on the flagellation of the vibrio were examined, and these two characters of the organism were reconsidered by way of comparison with those of Vibrio fischeri. The experimental results together with considerations are given as under. 1) NaCl tolerance : The lower limit falled to 0.1% after consecutive culture in the media containing 0.3% NaCl. The upper limit, in contrast with this, raised to 6% in case of the media with 4% NaCl. The range of 0.1 to 6% is applicable to the NaCl tolerance range of this organism in view of these results. 2) flagellation: Cells having more than one flagellum at one pole occurred in cultures grown on nutrient agar plate, of which the higher the NaCl concentration (0.5-4.5%), the higher the percent occurrence (0.22-20%). Cells, however, had one polar flagellum in cultures grown in nutrient broth except in the broth with extremely high concentration (4%) of NaCl. Accordingly it may be safely said that the flagellation of this organism is monotrichous. In conclusion it is impossible to differentiate this organism provisionally classified as Vibrio anguillicida BRUUN and HEIBERG in the previous report (MUROGA et al., 1976a) from Vibrio fischeri in terms of the above-mentioned two characters.
From May in 1975 to October in 1976, field investigations were made on dactylogyrids infestation on carp cultured in ponds at Hiroshima Prefectural Freshwater Fish Experiment Station. The results obtained are summarized as follows: 1) Dactylogyrus extensus and D. minutns were observed on fish of all ages almost throughout the year. 2) Apparent seasonal changes in abundance of both the dactylogyrids were recognized, and the changes seem to depend mainly on the water temperature. 3) D. extensus and D. minutus increased in abundance in the spring and the fall. The incresse of the former species was remarkable in the spring, and that of the latter in the fall. Both the species decreased conspicuously at the mid summer. 4) The same tendency of the above-mentioned changes in D. extensus was confirmed by experiments. D. extensus apparently increased in number with artificial raise of water temperature from 11°C to 20°C, and decreased sharply when the water temperature was over 20°C and reached about 25°C.
ISHII(1931) described a nematode from the caudal fin of Japanese crucian carp, Carassius auratus (LINNé), under the name of Filaria carassii and stated that the gravid female of the nematode had three minute sharp protuberances around the mouth. Later, YAMAGUTI (1961) referred this species to the genus Philometra, but FURUYAMA (1934) and IVASHKIN et al. (1971) regarded it as the synonym of Philometroides sanguinea (RUDOLPHI, 1819) RASHEED, 1963. We found the eleven gravid females of ISHII's species in the caudal fin of nine of the 76 crucian carp which were obtained from a game fishing pond at Ichikawa city in Chiba prefecture in March, 1975, and examined for the nematode. The infected nine fish were 18-25 cm in body length. Five specimens of the eleven gravid females were examined morphologically. Possessing numerous bosess on the cuticular surface of their bodies, ISHII's species had to be certainly combined with the genus Philometroides and had to be distinguished from P. sanguinea in which the presence of the pharyngeal teeth was never described by any writer, though the sizes of gravid females, eggs and larvae were the same each other. We suggested from the combination of this species that the two characters of the genus Philometroides, that was, “Head with papillae” and “Oesophageal teeth absent”, had to be eliminated from the generic diagnosis proposed by RASHEED (1963). Philometroides carassii (ISHII, 1931) n. comb. (Figs. 1-4): Body filiform, tapered anteriorly and posteriorly with bluntly rounded end, 40-45 mm long by 0.8-1.1 mm wide when fixed in 5% formalin. Cuticle with numerous bosses irregularly scattered. Cephalic and caudal papillae absent. Three cuticularrized pharyngeal teeth present around the mouth. Pharynx swollen just under the mouth, 3.0-3.5 mm long by 0.11-0.15 mm wide at the swelling. Nerve ring 0.25-0.28 mm from the head end. Intestine 0.24-0.37 mm wide, ended blindly near the tail end. Anus and vulva absent. Uterus opposed. Anterior ovary 1.7-2.5 mm long by 0.05-0.08 mm wide and posterior ovary 1.2-2.0 mm long by 0.03-0.04 mm wide. Eggs spherical, thin-shelled, 26-40μ in diameter. Larvae filiform with rounded head and shrply pointed tail, 0.34-0.41mm long by 13-18μ wide. Types: Deposited in the National Science Museum, Tokyo. Cat. no. NSMT-As-1428.