Abstract. Mass mortalities of hatchery‐reared Japanese parrotfish larvae and juveniles, Oplegnathus fasciatus (Temminck & Schlegel), have occurred in Nagasaki Prefecture. Light and electron microscopic examinations showed that the only consistent histopathological feature was extensive nervous necrosis in the spinal cord, spinal ganglia and brain. Numerous non‐enveloped virus particles, icosahedral in morphology and measuring about 34 nm in diameter, were found in the cytoplasm of affected neurones and glial cells. Such nervous necrosis is believed to be the major cause of the mass mortalities of hatchery‐reared Japanese parrotfish larvae and juveniles.

The hemagglutinating properties of Edwardsiella tarda isolated from fish were investigated. Hemagglutination of E. tarda was not inhibited by D-mannose but was strongly inhibited by fetuin and N-acetylneuraminic acid. Extraction of hemagglutinating activity from bacterial cells was achieved using n-octyl-L-D-thioglucoside (NOTG), and the NOTG extracts were fractionated by sucrose density gradient ultracentrifugation. Sodium dodecyl sulfate^polyacrylamide gel electrophoresis analysis of the fractions revealed that a 19.3-kDa protein band appeared in the fractions exhibiting highest hemagglutinating activity. In an immunoblot analysis of NOTG extracts from 18 strains of E. tarda, the 19.3-kDa protein was detected only in the extracts possessing hemagglutinating activity. The predicted amino acid sequence of a 534-bp gene encoding the 19.3-kDa protein was identical to fimbrial subunit (FimA) of E. tarda by FASTA homology search. These findings suggest that fimbriae are implicated in the hemagglutination of E. tarda.

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ABSTRACT-Streptococcus iniae is known as an important marine and freshwater fish pathogen worldwide. In this paper, we characterized two serological phenotypes in Japanese S. iniae isolates, mainly from Japanese flounder Paralichthys olivaceus.

Peritrophic membranes are formed in all the 25 species examined. The peritrophic membranes of free-living and commensal notodelphyoid copepods are formed in the whole region of the mid-gut, whereas they are formed in the posterior region of the mid-gut in some cyclopoid associates of marine bivalves and parasitic copepods.The peritrophic membranes of free-living copepods are generally thicker than those of parasitic copepods.A chitosan test and histochemical and ultrastructural examinations revealed that the peritrophic membranes of free-living Tigriopus and parasitic Panaietis consist of chitinous microfibrils arranged in a disperse texture and a ground substance containing acid mucopolysaccharides and proteins, and chitinous microfibrils of Tigriopus are much thicker than those of Panaietis. In Lernaea, faecal pellets are produced at considerably regular intervals.On the basis of these findings some possible roles of the peritrophic membranes of copepods are discussed.