We conducted a comparative study of Aeromonas salmonicida strains isolated in the Northwest of Spain from salmon and trout (Oncorhynchus mykiss, Salmo salar and S. trutta) cultured in fresh and sea waters with reference strains from different countries. Regardless of the geographic origin and source of isolation, all strains were biochemically and serologically similar, belonging to A. salmonicida subsp. salmonicida. All the isolates exhibited a uniform plasmid pattern. The majority of them (93%) carried three small plasmids of 3.6, 3.5 and 3.4 Megadaltons (Md). In addition, a fourth plasmid of 4.2 Md was present in 21 of the 32 strains examined. Only in some isolates a large plasmid was detected in the range of 40-55 Md. A high number of the Spanish isolates were resistant to oxolinic acid and flumequine. However no correlation between plasmid content and drug resistances was observed. The phenotypic and genetic homogeneity of the pigmented A. salmonicida strains make very difficult the determination of the origin of furunculosis in a particular geographic area.
Histopathological study was made on cultured striped jack, Caranx delicatissimus with yellow fat disease. The diseased fish were collected at a fish farm on Shikine Island, Tokyo in May, 1989. These fish showed black discoloration on the body surface and were emaciated. The adipose tissues in the abdomen and the inner side of the operculum had changed to a yellowish color, with discoloration and atrophy of the liver. Histologically, steatitis, fat necrosis, multinucleated syncytium formation, deposit of altered lipids, small granuloma formation and deposit of ceroid-like lipopigments in macrophage centres (MC) were observed in the adipose tissues. Lipopigments similar to those found in the adipose tissues were also observed in MC formed in the liver, in the intra-muscular connective tissue of the trunk muscle, in the lamina propria of the pyloric caeca and the intestine, and under the endothelium of the sponge layer of the cardiac muscle. Ceroid-like lipopigments were also found in the cytoplasm of the hepatic cells and melano-macrophage centers in the spleen and the kidney. Hemolytic anemia and myopathy of the trunk muscle were also found. From the results, it is suggested that the morbid state of this disease corresponds to that of the yellow fat disease reported in many species of mammals.
A cell line, designated as FF-11, was developed from Japanese flounder (Paralichthys olivaceus) fin. This epithelioid cell has been passed 45 times in a period of 2 years in Leibovitz's L-15 medium supplemented with 20% fetal bovine serum (FBS) at 20deg;C. A modal number of chromosomes at passage 42 was 48, which is the same as that of normal flounder somatic cells. The temperature range from 20 to 28deg;C supported the growth of FF-11 cell and optimal growth occurred at 25 to 28deg;C, but 37deg;C was lethal. Cells were able to be stored at a -80deg;C with 10% dimethyl sulphoxide for at least 12 months and no mycoplasmal, bacterial or fungal contaminations were detected. The FF-11 cell line was susceptible to yellowtail ascites virus (YAV) and Rhabdovirus olivaceus (HRV), but the susceptibility was lower than those of established fish cell lines (FHM, EPC, CHSE-214, RTG-2). It was tried to isolate flounder herpesvirus (FHV), the causative agent of epidermal hyperplasia of flounder larvae, by FF-11 cell, but to no avail.
Genomic RNA was extracted from purified virions of hirame rhabdovirus (HRV), infectious hematopoietic necrosis virus (IHNV), and viral hemorrhagic septicemia virus (VHSV). The full-length RNA was analyzed using formaldehyde agarose gel electrophoresis followed by ethidium bromide staining. Compared with an internal RNA size standard, all three viral genomic RNAs appeared to have identical relative mobilities and were estimated to be approximately 10.7 kilobases in length or about 3.7 megadaltons in molecular mass. Structural protein synthesis of HRV, IHNV, and VHSV was studied using cell cultures treated with actinomycin D. At 2 h intervals, proteins were labeled with 35S-methionine, extracted, and analyzed by SDS-polyacrylamide gel electrophoresis and autoradiography. The five structural proteins of each of the three viruses appeared in the following order : nucleoprotein (N), matrix protein 1 (M1), matrix protein 2 (M2), glycoprotein (G), and polymerase (L) reflecting both the approximate relative abundance of each protein within infected cells and the gene order within the viral genome.
The parasitic ciliate Trichodina truttae Mueller, 1937 is redescribed from silver-impregnated specimens collected from the body surface of chum salmon fry (Oncorhynchus keta) reared in five hatcheries of Hokkaido and northern Honshu, Japan. The description is supplemented by scanning electron microscopic observations. The distinguishing morphological features include its large size (body diameter 115-178 μm), high number (10-23) of radial pins per denticle, and the presence of two markedly different lengths of cilia within the adoral ciliary spiral. Geographical variation was observed in the body size and number of denticles. This is the first record of T. truttae from Japan.