The influences of cooling on the intestinal microflora of the Japanese eel and on the persistence of an administered virulent strain of Aeromonas hydrophila A10 in the intestine of the eel were investigated. A change in the intestinal microflora was commonly observed in spite of differences in the length of the treatment (cooling). After being placed in chilled water (10°C lower than control temperature) for 2 hours and for 12 hours, Streptococcus increased at first in proportion to the majority of the intestinal microflora, while Aeromonas decreased. Two or three days after the treatment, the relation between them was reversed, i. e., Aeromonas increased and Streptococcus decreased. During repeated treatments, Streptococcus was predominant and decreased four or five days after the first treatment, but Aeromonas was rarely isolated. There was no difference in the temperature ranges for growth of the isolates from the intestine of the eel, they were between 14 and 45°C. The persistence of the administered A. hydrophila A10 was prolonged in the eels stressed with temperature decrease, but the infection was not established. From these results the authors concluded that the physiological function of the eel was changed by the rapid decrease of the water temperature and it caused the fluctuation of the intestinal microflora. This physiological change might affect an exogenous pathogen in the intestine.
Two species of marine cercariae were found in trochid gastropods from Hachijo Island, Japan and the specific names Cercaria hachijoensis and Cercaria rhipidocaudata are proposed. The former species was obtained from Trochus sacellus rota, Tectus pyramis and Omphalius nigerrimus and the latter from T. sacellus rota. C. hachijoensis is a cotylocercous cercaria with a single-pointed stylet, five pairs of penetration gland cells, long intestines reaching to the level of the posterior end of acetabulum, a flame cell formula of 2[(2+2)+(2+2)]=16 and develops in sporocysts. C. rhipidocaudata has a fan-shaped tail bearing three pairs of projections, a pair of single-pointed stylets, a flame cell formula of 2[(2+2)+(2+2)]=16 and develops in rediae.
From Edwardsiella tarda EF-1 strain, three antigens were obtained: lipopolysaccharide (LPS), culture filtrate and formalin killed whole cells. Eel were injected intramuscularly with the antigens twice at an interval of one week. The agglutination and passive hemagglutination titers in serum were determined three weeks after the second immunization. In the another experiment, eel were challenged by intramuscular injection with live bacteria three weeks after the second immunization and the agglutination titer was determined in the serum of the surviving eels. Antigenic relationships between the LPS and the culture filtrate were examined by OUCHTERLONY method and the immunoelectrophoresis. All the immunized eel showed an increase in titer to the three antigens, but a large increase in the titer was not observed. The highest survival rate was recorded in challenged eel immunized with LPS, which indicated the LPS role may correlate with the protective effect of the vaccine. Agglutination titer increased significantly in the serum of the immunized eel, but no correlation between survival rate and agglutination titer was observed among the immunized groups. The results suggest that the agglutination titer using whole cell antigen does not correlate with the level of the protection observed in eels. The increase in the titer with whole cell antigen was considered to be a function of an antigen detected in the LPS and the culture filtrate.
In a Vibrio anguillarum strain passaged through ayu (Plecoglossus altivelis), the LD50 value against ayu by the water-borne challenge method did not change from that of the original strain freshly isolated from diseased fish. The ayu were reproducibly infected with the passaged strain by the water-borne method in which the fish were first exposed to 5.32% NaCl solution and then to a suspension of V. anguillarum cells. The symptoms in ayu infected by this challenge method were observed to be very similar to the symptoms of a natural vibriosis infection. The LD50 value against fish exposed first to NaCl solution and then to the cell suspension was lower than that of fish exposed to only the cell suspension. This challenge method, incorporating initial exposure to a 5.32% NaCl solution followed by exposure to a Vibrio cell suspension, provided a clear difference in mortality between vaccinated and non-vaccinated fish. High level protection against vibriosis was observed in fish vaccinated by immersion in V. anguillarum cells which had been formalinized, washed, and pelleted or which had been formalinized, washed, and lyophilized.
The mouth-parts of Argulus coregoni and A. japonicus are described based on SEM observation. A smooth upper lip and a rugose lower lip with small rows of teeth form the mouth opening. Two types of sensilla lie on the lips around the opening. Mandibles and labial spines are found in the buccal cavity. The preoral sting has a globular tip, a ventral, subterminal glandular pore and a dorsal, subterminal minute pore possibly of sensory in function. Some differences in the buccal folds and a pair of spines on the mouth tube are found between the adults and larvae of A. coregoni. But there are no significant differences in the mouth-parts between the two species.
Yearling masu trout Oncorhynchus masou were experimentally infected by Argulus coregoni and effects of the infection on the host blood _parameters were examined 24 hours and 10 days after infection. Plasma glucose concentration increased in the infected group after 24 hours. After 10 days, 1) erythrocyte and leucocyte counts, hemoglobin concentration and hematocrit value decreased in the infected group; 2) plasma total protein, total cholesterol and calcium concentrations in the infected group decreased more than those in the uninfected; 3) immature erythrocyte count was remarkably high in some infected fish; and 4) there was no distinct difference in the glucose level between the infected and uninfected group. No significant differences were observed in thrombocyte count and plasma phosphate concentration.
Two new species of the genus Kudoa (Myxosporea: Multivalvulida) were described; Kudoa iwatai sp. n. from the lateral musculature of Pagrus major and Oplegnathus punctatus and K. shiomitsui sp. n. from the pericardial cavity and ventricle of Takifugu rubripes. Both were discovered from fishes cultured at farms on the coast of Kyushu, Japan. Spores of both species were differentiated from other members of the genus Kudoa on the basis of a through recording of their shape, structure and dimentions by means of the light microscope and scanning electron microscope.