The causal relationship of atypical cellular gill disease (ACGD) and Plecoglossus altivelis poxvirus-like virus (PaPV) in ayu Plecoglossus altivelis was studied through a transmission experiment in which naive fish were exposed to the filtrate of a homogenate of diseased fish gills containing PaPV. ​ACGD symptoms, including lethargy and abnormal swimming such as staying away from the water current with open opercula, were observed in the fish exposed to the virus at 4 days post-exposure (dpe) at 20°C. ​The cumulative mortality in the virus-exposed fish groups with and without sodium nifurstyrenate pretreatment was 82% and 56%, respectively. ​Dead fish showed atypical gill epithelial cells on gill filaments with PaPV DNA at 10⁷–10⁹ copies/mg level. ​In addition, fish were experimentally infected at different rearing temperatures of 18°C, 23°C and 28°C. ​Fish death was first observed at 15 and 10 dpe in the experimental groups at 18°C and 23°C, with cumulative mortality of 58% and 42%, respectively. ​However, there was no mortality in fish reared at 28°C. ​These results suggest that the etiological agent of ACGD in ayu is PaPV, and ACGD occurrence can be influenced by the rearing water temperature.

In 2013, four cases of digenean infection occurred among 0-year Seriola dumerili, imported from China and subsequently cultured in Kagoshima Prefecture, Japan. ​In each case, a single immature worm was recovered from the abdominal cavity, kidney, or skeletal muscle, associated with black viscous substances, probably of parasite origin, suggesting that the parasite was migrating within the fish body. ​From morphological and molecular analyses, the digenean was identified as Hirudinella ventricosa. ​No such infection was recorded among 1,968 cultured Seriola spp. examined in Kagoshima during 2012–2018 except for the four cases. ​In 2017, black to brown substances were noticed in the fillets of Seriola quinqueradiata at a processing factory. ​The fish with contamination had been cultured for two years from wild seeds caught along the coast of Kagoshima Prefecture. ​No worm was found, but the 28S rRNA gene sequence analysis demonstrated that they were originated from H. ventricosa. ​Both the infection of S. dumerili and the contaminated fillets of S. quinqueradiata are assumed to be the cases of larva migrans caused by the hirudinellid digenean.

The present study investigated the genotype of Ichthyobodo spp. that caused six cases of ichthyobodosis in various salmonid species cultured in freshwater, in Hokkaido, Japan, through molecular phylogenetic analysis of the parasite ribosomal RNA gene (rDNA). ​Polymerase chain reaction (PCR) and scanning electron microscopy (SEM) were performed to distinguish the genotypically differentiated Ichthyobodo spp. ​The parasites were identified as genotypes I (I. necator sensu stricto), II (I. salmonis), or III (Ichthyobodo sp.). ​The present PCR method could completely distinguish between genotypes I, II and III using the electrophoresis pattern of PCR products from the parasite rDNA. ​Our SEM observations were able to SEM observations were able to morphologically distinguish genotype I from other two genotypes, but not between genotype II and III.

無機物の食品添加物で構成されるオキシリンクSPのサケ科卵のミズカビ病に対する防除効果を調べた。室内試験においてSaprolegnia属菌5種に対するオキシリンクSPの殺菌効果を検討した結果，30分間の薬浴では10,000倍以下の希釈で殺菌作用を示した。野外試験では，Saprolegnia属菌以外の菌類が発育したサクラマス卵を除き，ニジマスおよびイワナ卵での菌糸発育抑制効果を確認した。魚卵毒性については，生産上大きな被害はないが，ニジマス卵の発眼率および孵化率に影響を与えた。一方，イワナ卵およびサクラマス卵に対する影響は認められなかった。オキシリンクSPによる薬浴はサケ科卵を対象としたミズカビ病の防除に有用であるが，薬浴条件について検討する必要がある。