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.
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.
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.
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.