Hundreds of thousands of six-month-old carp which might harbour Bothriocephalus opsariichthyd s YAMAGUTI at the rate of about 20 per cent were cultured in a big swamp in Sanami district, Gunma prefecture. Hundreds of fish were drawn randomly from there and were kept in a net cage of 1.5 m³set in the other pond of 1.2 m deep in same district during the period from November, 1975 to May, 1976. Fifty eight fish of them were sacrificed for examination for the cestode once a month.
The rate of fish which had the cestode fell suddenly from 17.3 per cent in November to 5.2 per cent in December, but the latter rate was maintained as it was until next May. Every living worm which stayed in host's intestine laid eggs again in April. It seems that the life cycle of this cestode may be turned only by the wintered adult worm.

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Kamala, Bithionol, Nicrosamide and Parbendazole were tried to use for the prevention of spreading of Bothriocephalus opsariichthydis YAMAGUTI, 1934. Every anthelmintics were administered to tens or hundreds of thousands of four-month-old carp, each of which was kept in five ponds in Nagano prefecture, on October in 1975. Fifty eight fish collected randomly from each pond were examined at 5 to 7 days after administration.
The rate of fish which harboured the cestode was markedly reduced with these anthelmintics, but the average number of worms remained in the host did not decrease. This result means that all of fish kept in a vast pond never equally took a diet containing drugs. Beside it is difficult for us to certify that all of fish administered were parasite-free, even if no fish harboured any worms was detected on the only abstracted sample. We conclude from above mentioned reasons that using of anthelmintics to the young carp before their first wintering is scarcely any significance for the prevention against this cestode.

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The therapeutic effects of ampicillin, applied orally, on the pseudotuberculosis of yellowtails, Seriola quinqueradiata and Seriola purpurascens, were studied.
1. Yellowtails artificially infected with P. piscicida were given ampicillin by oral route at the doses of 0.1, 1, 10 and 100 mg/kg·b.w. The mortality rate of each dose was 70, 40, 30 and 0%, respectively.
2. Ampicillin was also effective at the dose of 12 mg/kg·b.w. in reducing the mortality rate of yellowtails naturally infected with P. piscicida.

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The antibacterial and bactericidal activity of sodium nifurstyrenate (NFS-Na) and three therapeutic drugs were studied with Streptococcus sp.
The minimum inhibitory concentration (MIC) against Streptococcus sp. was 0.15 to 0.62 mcg/ml for NFS-Na, 0.31 to 0.62 mcg/ml for aminobenzylpenicillin, 1.2 to 2.5 mcg/ml for chioramphenicol, and 0.075 to 0.15 mcg/ml for tetracycline, respectively.
The bactericidal effect against Streptococcus sp. was observed at 5 mcg/ml of NFS-Na for 8 hrs and at 5 mcg/ml of ampicillin for 24 hrs, whereas chloramphenicol and tetracycline revealed no bactericidal effect at 10 mcg/ml for 24 hrs.

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In the previous paper, the pathogenic organisms isolated from the scale protrusion disease of carp fishes, were identified as Aeromonas liquefaciens according to the morphological, biochemical and biological properties.
In this study, the serological relationship between these isolates and related organisms was investigated. The results obtained are as follows:
1. Aeromonas punctata strain ATCC-11163 and A. liquefaciens strain UT-62 were agglutinated by antisera of the isolated strains CA-1 and CB-1. However, A. hydrophila strain NRRL-B-909 and A. salmonicida were the organisms which failed to react with antisera prepared against strains CA-1 or CB-1.
2. Agglutinin-absorption studies were carried out in order to examine further the antigenic relationship between the isolates and strains ATCC-11163 or UT-62. As the result of experiments, it was confirmed that the isolates, strains ATCC-11163 or UT-62 was not complete antigenical agreement.

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Detailed morphology and life history of Trichodina reticulata, isolated from the mucous of body surface, fins and gills of goldfish and other carps of Japan, were studied.
Generally dome-shaped body measures from 50-90μ in diameter and height of the body is 15-35μ. The diameter of sucking disc is 44-80μ and that of the denticulate ring 42-72μ and the horse-shoe shaped macronucleus 22.5-49μ, the thickness being 6-7μ. Number of denticle is most often 24 and 27(20-31) and radial pins per denticle is 10(7-10). Dimensions of denticle: length of blade 4.5-7.5μ; length of ray 5.5-7.5μ; width of central conical part 2.5-4μ and length of denticle 5-11μ. Width of border membrane 3.5-6μ. Large spindle-shaped micronucleus (7-15×2-5μ) lies in a shallow depression on the outside of right arm of the macronucleus. The central part of the sucking disc is separated into several fields of cell-like structures. Both contractile and food vacuoles are distinct. Velum is delicate and transparent. The ciliate moves by means of velum, aboral cilia and the membranelles. Both ciliary girdles lie in usual manner. Adoral zone forms a spiral of about 370°.
Binary fission starts with the enlargement of the ciliate, changes in shpae of the macronucleus, becoming short and thick with randomly distributed chromatin; finally dividing into two dumbell-shaped equal halves. The micronucleus swells and divides mitotically. Prior to the onset of fission the anlage of new denticulate ring appears between the old ring and circumference of the disc. Indentations appear in the velum and breaks appear in the striated band below the velum. Contractile vacuole divides to produce one for each daughter cell. After division the old ring with half the number of denticles gradually disappears and about twice the number of denticles are developed in the new outer ring. Similarly radial pins and cilia also restore original number.
A few cases of conjugation were found where both iso and anisogamous types were observed. The large exconjugant contains one functional nucleus, the synkaryon, which divides three times and thus forming eight micronuclei, seven of them micronuclear anlagen and one functional micronucleus. The cell division continues until each of the daughter individuals contain one macronuclear anlage and a micronucleus. In this case the number of denticles in the new ring of the daughters is the same as in the old ring

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As previously reported (MUROGA et al. 1973), red spot disease (Pseudomonas anguilliseptica infection of cultured eels) prevails in brackish-water ponds when the water temperature is below 20°C, and ceases when it rises to 27°C.
In this paper, physiological characteristics of the causative bacterium, P. anguilliseptica were investigated, and the results were discussed with respect to the epizootiological facts described above. The experimental results and conclusions are summerized as follows.
1) Effects of pH, NaCl and temperature on the growth of the organism: It grew in nutrient broth at pH 5.3-9.7 (Optimum range 7-9), at NaCl 0-4% (Optimum 0.5-1%) and at temperatures from 5°C to 30°C (Optimum 15-20°C).
2) Effects of NaCl or chlorinity on the survival of the organism: The period of survival was prolonged with the increase in concentration of NaCl or chlorinity, and the organism survived more than 200 days in sea water and in diluted sea waters (Cl≥1.9‰). This nature of the organism is considered to be closely related to the fact that the disease prevails not in freshwater ponds but in brackish-water ponds.
3) Effects of temperature on the survival and the motility of the organism: The organism survived in diluted sea water (Cl 5.6‰) more than 40 days at 27°C and below, but it perished within 7 days at 30°C and above. The motility of the organism was gradually inactivated by increasing incubation temperature, and was poor above 25°C.
4) The above-mentioned nature of the organism against temperature is considered to be the main cause of the temperature-dependence of the epizootic.

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Pseudomomas anguilliseptica infection of the Japanese eel is a new disease that was confirmed in 1971 and named red spot disease. This disease has prevailed in spring and autumn and has resulted in mass mortalities. Histopathological studies were made on 55 diseased eels that had petechial hemorrhages in the body surface and fins. Anatomically they showed congestive swelling of liver, atrophy of spleen, kidney, and pericard-epicarditis.
Histopathological studies indicated that infected lesions appeared in dermis, subcutaneous adipose tissue, interstitial tissue of the body musculature, vascular walls, bulbus arteriosus and heart.In such lesions bacteria multiplied profusely and resulting inflammation was serous exudation and cellular infiltration-proliferation composed of activated mesenchymal cells, wandering, large mononuclear cells, large juvenile cells and a small number of neutrophils. Many minute hemorrhages occurred in affected dermalloose connective tissue, and small hemorrhages occurred in the intraepithelial papillary tissue. In the stages of generalized infection to the septic condition various pathological changes were observed in the visceral organs, that is, congestive edema and intensive fatty degeneration of the hepatic cells in the liver; the reactions mixed with serous exudation, tissue liquefaction and cellular proliferation in the spleen; infectious glomerulitis, activation of the reticulo-endothelial cells lining sinusoids, and atrophy of the hematopoietic tissue in the kidney.
On the basis of these findings diseased eels manifested with petechial hemorrhages in the body surface are thought to be in an advanced condition of the disease.

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In the previous report, the biochemical characteristics of 22 strains of a vibrio isolated from diseased rainbow trout were presented (OHNISHI and MUROGA 1976).The organism differs from Vibrio anguillarum in some biochemical characters, and it was given a tentative name of Vibrio sp. RT group.
In this paper, physiological characteristics and pathogenicity of the organism are described.
The experimental results are summerized as follows.
1) Effects of sodium chloride, temperature and pH on the growth of the organism: It grew in broth (1% peptone +1% heart extract) at NaCl 0.5-5% (optimum range 1-3%), at temperatures 15-30°C (optimum 20-25°C), and at pH 6-9 (optimum 7), respectively.
2) Pathogenicity: The organism injected intramuscularly killed rainbow trout and carp.
However, it did not kill mice by intraperitoneal injection.
3) Survivalin waters: The organism survived in sea water more than 4 weeks, but it perishedin freshwater within a few hours. And it is assumed that the organism can not be established in freshwater.
4) From the facts that trout farms investigated are isolated far from sea and these trout have been fed only on dry pellet in recent years, it is thought that some carrier including trout itself must participate in outbreaks of this vibriosis in trout farms.

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Studies were made on tissue levels of chloramphenicol (CP) in cultured eel, Anguilla japonicawhich were given 50 and 100 mg of CP per kilogram of body weight. The fish were fed the drugcontaining artificial food once a day for successive 5 days prior to the drug analysis. The water temperature was 23.8 to 25.4°C, average 24.7°C, during the course of experiment.
The highest tissue levels of CP were obtained 6 hours after last medication. The highest levels of CP were found in the kidney and the lowest levels were in the liver. The levels of CP in those tissues became almost undetectable after 48 hours.
Total nitro compound levels in tissues were also analyzed (Table 1 and 2).

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Recently a disease which is characterized by swelling of the kidney has been observed among pond-cultured ayu, Plecoglossus altivelis in Tokushima Prefecture. Yeasts were frequently isolated from the kidney of diseased fish. These yeasts were identified as Candida tropicalis and C. sake.
The swollen lesion of the kidney was histopathologically showing necrosis of renal tubules, edematous dissociation of hematopoietic tissue and dilatation of sinusoids.
Histopathological observation could not find the relationship between swelling of the kidney and these yeasts. Thus, occurrence of yeasts in the kidney is very likely to be the result of secondary invasion.
We could not make clear the cause of this unknown disease.

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